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Fire Protection Engineering Calculators

Q: What safety margin should a sprinkler system have between demand and water supply?

NFPA 13 does not set one. The system demand, with the hose stream allowance added, has to fall at or below the water supply curve at the total flow. Many authorities having jurisdiction and some insurers ask for a cushion on top of that, often a fixed pressure such as 5 or 10 psi or a percentage of the available pressure, to cover seasonal and long-term changes in the supply. Confirm the requirement for the project before relying on a margin.

Q: How is friction loss calculated in sprinkler piping?

NFPA 13 uses the Hazen-Williams formula, p = 4.52 Q^1.85 / (C^1.85 d^4.87), which gives the loss in psi per foot for a flow Q in gpm, a C-factor for the pipe material and condition, and the internal diameter d in inches. Fittings and valves are added as equivalent lengths of pipe. Where the fluid is not water at normal temperature, such as an antifreeze solution, the Darcy-Weisbach equation with the Colebrook friction factor is the more accurate method, and NFPA 13 requires it for some antifreeze systems.

Q: How do you calculate the available flow from a hydrant flow test?

NFPA 291 projects the test to a lower residual pressure with QR = QF x (hR / hF)^0.54. QF is the flow measured during the test, hF is the pressure drop during the test (static minus residual) and hR is the pressure drop to the target residual, usually 20 psi. On N^1.85 graph paper the static point and the test point join in a straight supply line.

Q: Can results from these calculators be used in a permit submittal?

They are engineering aids for sizing, checking and reviewing. Permit submittals usually need complete calculations prepared by the responsible designer, often in hydraulic calculation software, and signed or sealed as the jurisdiction requires. Each tool page lists its method, assumptions and sources so a reviewer can follow how a number was reached.

Q: Are the calculators free, and is anything I enter stored?

They are free, with no account or download. Every calculation runs in your browser and nothing you enter is sent to DGA. A few tools can keep your inputs in your own browser so they are there when you come back.

Q: Which code editions do the calculators follow?

Each calculator page names the standard it follows, and most list their references with the edition used. Adopted editions vary by state and city, so confirm what the authority having jurisdiction enforces. The Fire Code Cheat Sheet lists the building and fire code editions in force in the states DGA serves.

Free calculators for the checks fire protection engineers run every day, from hydrant flow tests to smoke layer descent. Nothing to download or license: enter your numbers and get the answer, with the method and sources on every page.

Based on NFPA standards, the IBC and IFC, and NRC and NIST references
Free, runs in your browser; your inputs stay on your device
Screening tool, not reviewed or sealed by a licensed engineer
Last updated October 2026

Essential Everyday Tools

Jump straight into the most frequently used calculators for water supply, pump performance and friction loss.

NFPA 291Hydrant Flow Test CalculatorPitot flow, available flow at 20 psi and the supply curve on N^1.85 paper.Open calculator NFPA 20 / NFPA 25Fire Pump Test Curve PlotterRated, shop and field curves, speed correction and a printable test report.Open calculator NFPA 13 / NFPA 291Sprinkler Demand vs. Water Supply AnalysisSystem demand and hose allowance against the supply curve, with the safety margin.Open calculator NFPA 13Hazen-Williams Friction Loss CalculatorFriction loss for a pipe run with its fittings and valves, by the NFPA 13 Hazen-Williams formula.Open calculator

47 calculators in 9 disciplines, each tied to the standard or code it follows.

Water Supply and Hydraulics Calculators

Water supply analysis compares what the source can deliver with what the system needs. A hydrant flow test under NFPA 291 gives the static and residual pressures, and the flow available at 20 psi follows from Q_R = Q_F (h_R/h_F)^0.54, a straight line on N^1.85 graph paper. Friction loss in the piping comes from the NFPA 13 Hazen-Williams formula, or from Darcy-Weisbach with the Colebrook friction factor for antifreeze and other fluids. When the supply falls short of the demand, a fire pump is sized and tested under NFPA 20 and NFPA 25, and site fire flow comes from the construction type and floor area tables of IFC Appendix B.

Water Supply and Hydraulics Calculators: the standard or code each follows and what it calculates
Calculator	Standard or code	What it calculates
Hydrant Flow Test Calculator	NFPA 291	Pitot flow, available flow at 20 psi and the supply curve on N^1.85 paper.
Fire Pump Test Curve Plotter	NFPA 20NFPA 25	Rated, shop and field curves, speed correction and a printable test report.
Sprinkler Demand vs. Water Supply Analysis	NFPA 13NFPA 291	System demand and hose allowance against the supply curve, with the safety margin.
Hazen-Williams Friction Loss Calculator	NFPA 13	Friction loss for a pipe run with its fittings and valves, by the NFPA 13 Hazen-Williams formula.
Fire Flow Calculator (IFC Appendix B)	IFC 2021 Appendix B	Required fire flow and duration for one or more buildings on a site.
Darcy-Weisbach Friction Loss Calculator	NFPA 13	Friction loss for water or antifreeze with the Colebrook friction factor, compared with Hazen-Williams.
Fire Pump Sizing Calculator	NFPA 20	Net pressure, standard ratings, churn pressure check and a driver estimate.
Fire Sprinkler Pressure Tank Calculator	NFPA 22	Air pressure, air fraction and total tank volume for a sprinkler pressure tank.
Hardy Cross Pipe Network Calculator	NFPA 13	Flow split in parallel paths or a two-loop grid, balanced by Hardy Cross with Hazen-Williams.

Water supply and hydraulics calculators page

Sprinkler System Design Calculators

Sprinkler hydraulics under NFPA 13 start from the discharge equation Q = K√P. The design density and area set the flow each sprinkler must deliver, and the K-factor sets the pressure needed at the most remote sprinkler before the hydraulic program carries the calculation back to the source. NFPA 13 also governs the supports that hold the water-filled pipe: trapeze hangers sized by section modulus, and seismic sway braces sized by the zone of influence method.

Sprinkler System Design Calculators: the standard or code each follows and what it calculates
Calculator	Standard or code	What it calculates
Sprinkler K-Factor Calculator	NFPA 13	Flow, pressure or K-factor from Q = K√P, with velocity pressure and the 7 psi check.
Sprinkler Seismic Brace Calculator	NFPA 13	Zone of influence weight, C_p from S_s, horizontal load F_pw, brace force and l/r check.
Sprinkler Design Area and Demand Calculator	NFPA 13	Sprinklers in the design area, end sprinkler flow and pressure, and a quick system demand with hose.
Sprinkler Trapeze Hanger Calculator	NFPA 13	Equivalent span, required section modulus and the lightest pipe or angle trapeze that works.

Sprinkler system design calculators page

Special Hazard Suppression Calculators

Gaseous agent and foam systems are sized by quantity rather than by density. NFPA 2001 sets the clean agent quantity from the protected volume, the design concentration (the extinguishing concentration times a safety factor) and the agent’s specific volume at the minimum design temperature. Carbon dioxide systems follow the NFPA 12 flooding factors for surface and deep-seated fires, and low-expansion foam systems follow the NFPA 11 application rates and discharge times.

Special Hazard Suppression Calculators: the standard or code each follows and what it calculates
Calculator	Standard or code	What it calculates
CO₂ Total Flooding Calculator	NFPA 12	Carbon dioxide quantity, discharge rate and hold for surface and deep-seated fires, following NFPA 12.
Clean Agent Quantity Calculator	NFPA 2001	Agent quantity, design concentration, altitude correction and occupied space check.
Foam Concentrate Calculator	NFPA 11	Foam solution, concentrate and water for tanks, seals and dikes.

Special hazard suppression calculators page

Fire Dynamics and Detection Calculators

Fire dynamics hand calculations estimate how a fire grows and what it does to the space around it. A t-squared design fire, Q = αt², feeds the Heskestad flame height and plume correlations, the Alpert ceiling jet correlations and the RTI response model that NFPA 72 Annex B uses to predict when a heat detector or sprinkler operates. NFPA 555 and the NRC’s NUREG-1805 Fire Dynamics Tools add the compartment methods, including the MQH correlation for hot layer temperature and the heat release rate needed for flashover.

Fire Dynamics and Detection Calculators: the standard or code each follows and what it calculates
Calculator	Standard or code	What it calculates
t-Squared Fire Growth Calculator	NFPA 72NFPA 92	Design fire curves with a peak cap, sprinkler control or full burnout from the fire load, plotted and downloadable as CSV.
Ceiling Jet Temperature and Velocity Calculator	NFPA 72 Annex B	Gas temperature and velocity under the ceiling at a sprinkler or detector, by the Alpert correlations.
Compartment Fire Temperature Calculator	NFPA 555	Upper layer temperature in a room fire: door open (MQH), forced ventilation or closed room.
Heat Detector and Sprinkler Activation Time Calculator	NFPA 72 Annex B	When a heat detector or sprinkler operates in a growing or steady fire, from its RTI, rating and spacing.
FDS Mesh Size Calculator	NIST FDS User's Guide	D, cell size for coarse, moderate and fine D/dx, and FDS-friendly IJK cell counts for a domain.
Fire Plume Temperature and Velocity Calculator	NFPA 92NFPA 72 Annex B	Centerline temperature, gas velocity and plume width at a height above the fire, with a profile chart.
Flame Height Calculator	NFPA 92	Mean flame height from heat release rate and fire area, with the NFPA 92 limiting elevation and a scale sketch.
Flashover Calculator	NFPA 555	Heat release rate for flashover by the MQH, Babrauskas and Thomas methods.
Time to Ignition Calculator	NUREG-1805	Piloted ignition time of thick and thin solids, critical heat flux and the flux needed for ignition.
View Factor Calculator	NUREG-1805	Configuration factors for rectangles and flame cylinders, with superposition and incident heat flux.

Fire dynamics and detection calculators page

Smoke Control and Tenability Calculators

Smoke control design under NFPA 92 and IBC Section 909 works from the fire plume: the mass flow entering the smoke layer sets the exhaust rate that holds the layer at its design height, and the smoke filling equations show how fast it descends with no exhaust running. Pressure differences from stair pressurization and stack effect are checked against the door opening force limit. Tenability is judged by visibility through smoke and by the fractional effective dose (FED) of heat and toxic gases in ISO 13571, and tunnel ventilation uses the NFPA 502 critical velocity to stop smoke backlayering.

Smoke Control and Tenability Calculators: the standard or code each follows and what it calculates
Calculator	Standard or code	What it calculates
Atrium Smoke Exhaust Calculator	NFPA 92	Plume flow, exhaust rate, plugholing limit and number of inlets for an atrium.
Door Opening Force Calculator	NFPA 92NFPA 101	Opening force under pressurization, the 30 lbf check and the largest allowable pressure difference.
FED Tenability Calculator	ISO 13571	Time to FED 0.3 and 1.0 from carbon monoxide, hydrogen cyanide, carbon dioxide and heat, held constant or ramping up.
Smoke Layer Descent Calculator	NFPA 92	Smoke layer height over time in an atrium, steady or t-squared fire.
Stack Effect Calculator	NFPA 92	Stack effect pressure by height, neutral plane location and leakage flow through a gap.
Tunnel Critical Velocity Calculator	NFPA 502	Air velocity needed to stop smoke backlayering in a tunnel fire, by the 2026 NFPA 502 Annex D equations.
Visibility in Smoke Calculator	NFPA 92	Visibility of exit signs, doors and walls through smoke, from extinction coefficient, optical density or fuel burned.

Smoke control and tenability calculators page

Egress and Occupant Load Calculators

Means of egress sizing starts with the occupant load: the floor area of each space divided by its occupant load factor in the IBC or NFPA 101. The occupant load sets the required width of stairs and doors and the minimum number of exits. For timed egress and performance-based designs, the hydraulic model of crowd movement estimates how long a floor takes to clear and which door or stair controls the flow.

Egress and Occupant Load Calculators: the standard or code each follows and what it calculates
Calculator	Standard or code	What it calculates
Egress Time Calculator	Hydraulic egress model	Movement time through doors and stairs, the controlling component and the queue.
Occupant Load Calculator	IBCNFPA 101	Occupant load by area, required stair and door width, and the number of exits.

Structural Fire Resistance Calculators

The building code accepts calculated fire resistance alongside tested assemblies. IBC Section 722.5 adjusts the thickness of sprayed fire-resistive material when a listed design is applied to a steel member with a different weight-to-heated-perimeter (W/D) ratio, and AWC NDS Chapter 16 calculates the effective char depth and residual section of exposed heavy timber and glulam. NFPA 557 quantifies the fire load density of the combustible contents that drive structural fire exposure.

Structural Fire Resistance Calculators: the standard or code each follows and what it calculates
Calculator	Standard or code	What it calculates
Char Depth Calculator	AWC NDS Chapter 16	Effective char depth, residual section and section properties of exposed timber, with a Eurocode 5 comparison.
Fire Load Density Calculator	NFPA 557	Fire load and fire load density from a survey of combustibles, compared with typical occupancy values.
SFRM Thickness Calculator	IBC 722.5	W/D, beam substitution and column SFRM thickness, plus protected steel temperature in a standard fire.

Structural fire resistance calculators page

Flammable Liquids, Gases and Radiation Calculators

Industrial and process hazards start with classification. NFPA 30 assigns a flammable or combustible liquid class from its closed-cup flash point and boiling point, and Le Chatelier’s rule gives the lower flammable limit of a gas mixture for comparison with the NFPA 69 limits. When a fire is postulated, the NUREG-1805 pool fire methods and the CCPS fireball correlations estimate its heat release rate and the radiant heat flux at a target, and the NFPA 80A radiation method addresses exposure from one building to the next.

Flammable Liquids, Gases and Radiation Calculators: the standard or code each follows and what it calculates
Calculator	Standard or code	What it calculates
Exterior Fire Exposure Calculator	NFPA 80A	Heat flux across a building separation, the NFPA 80A separation distance and the allowable openings.
Fireball Calculator	CCPS method	Fireball diameter, duration and heat flux at a target, with thermal dose and the distances to pain and burns.
Flammable Liquid Classification Calculator	NFPA 30	NFPA 30 class and GHS/OSHA category from flash point and boiling point, or estimated for a blend.
Gas Mixture LFL Calculator	NFPA 69	Mixture LFL and UFL by Le Chatelier’s rule, temperature effect, and percent of LFL against NFPA 69.
Pool Fire Heat Release Rate Calculator	NUREG-1805	Heat release rate, burning rate, burning duration and flame height for liquid pool and spill fires.
Pool Fire Radiation Calculator	NUREG-1805	Radiant heat flux to a target, separation distance and skin exposure times for liquid pool fires.

Flammables and radiation calculators page

Reference Data and Conversions

Fire protection calculations move between US customary and SI units constantly and lean on material property data. These references convert K-factor, design density, flow, pressure, heat release rate, heat flux and RTI following NIST SP 811, and tabulate heats of combustion and thermal properties of common materials with the public source for every value.

Reference Data and Conversions: the standard or code each follows and what it calculates
Calculator	Standard or code	What it calculates
Building Material Thermal Properties	NUREG-1805 data	k, ρ, c, thermal inertia and diffusivity of lining materials, with thermal penetration time.
Fire Protection Unit Converter	NIST SP 811	K-factor, density, flow, pressure, HRR, heat flux, RTI and 20 more quantities, every unit at once.
Heat of Combustion Table	NIST and NUREG-1805 data	Net, effective and gross heats of combustion with a heat release rate calculator.

Reference data and conversions calculators page

Project Planning

For owners and design teams starting a fire protection project in New York, New Jersey, Pennsylvania, Maryland or Delaware.

Planning toolProject Timeline EstimatorEngineering and AHJ review time for a fire protection project, by state and system.Open tool Planning toolFire Code Cheat SheetBuilding and fire code editions in force in the states DGA serves.Open tool

Methods and Formulas Behind the Calculators

Every calculator implements a published method. The table lists the main equations, the standard or reference each comes from and the calculators that use it. Units follow the source: US customary for NFPA 13 hydraulics and SI for most fire dynamics correlations. Each tool page gives the full method, its assumptions and its limits of validity.

Methods and equations used by the DGA fire protection engineering calculators
Method	Equation	Source	Used in
Water supply and sprinkler hydraulics
Hazen-Williams friction loss	p = 4.52 Q^1.85 / (C^1.85 d^4.87), psi per foot with Q in gpm and d in inches	NFPA 13	Hazen-Williams Friction Loss, Hardy Cross Pipe Network
Darcy-Weisbach with the Colebrook friction factor	Δp = f (L/D) ρv²/2, with 1/√f = −2 log₁₀[(ε/D)/3.7 + 2.51/(Re√f)]	NFPA 13	Darcy-Weisbach Friction Loss
Water supply projection	Q_R = Q_F (h_R/h_F)^0.54, plotted on N^1.85 graph paper	NFPA 291	Hydrant Flow Test, Sprinkler Demand vs. Water Supply Analysis
Sprinkler discharge	Q = K√P	NFPA 13	Sprinkler K-Factor, Sprinkler Design Area and Demand
Hardy Cross loop correction	ΔQ = −Σh / (1.85 Σh/Q)	Cross (1936)	Hardy Cross Pipe Network
Pump speed correction (affinity laws)	Q₂ = Q₁ (N₂/N₁), P₂ = P₁ (N₂/N₁)²	NFPA 20, NFPA 25	Fire Pump Test Curve Plotter
Pressure tank air pressure	P_i = (P_f + 15)/A − 15, psig, with A the air fraction	NFPA 22	Fire Sprinkler Pressure Tank
Fire dynamics and detection
t-squared design fire	Q = αt²	NFPA 72 Annex B, NFPA 92	t-Squared Fire Growth, Heat Detector and Sprinkler Activation Time
Flame height (Heskestad)	L = 0.235 Q^2/5 − 1.02 D, m with Q in kW	NFPA 92	Flame Height, Pool Fire Heat Release Rate
Ceiling jet temperature (Alpert)	ΔT = 16.9 Q^2/3/H^5/3 for r/H ≤ 0.18; ΔT = 5.38 (Q/r)^2/3/H beyond	NFPA 72 Annex B	Ceiling Jet Temperature and Velocity, Heat Detector and Sprinkler Activation Time
Detector and sprinkler response	dT_d/dt = (√u / RTI) (T_g − T_d)	NFPA 72 Annex B	Heat Detector and Sprinkler Activation Time
Hot layer temperature (MQH)	ΔT = 6.85 [Q² / (A_o√H_o h_kA_T)]^1/3	NFPA 555	Compartment Fire Temperature
Flashover heat release rate	Q_fo = 610 (h_kA_TA_o√H_o)^1/2 (MQH), 750 A_o√H_o (Babrauskas), 7.8 A_T + 378 A_o√H_o (Thomas)	NFPA 555	Flashover
Ignition time, thermally thick solid	t_ig = (π/4) kρc [(T_ig − T₀)/q″]²	NUREG-1805	Time to Ignition
FDS characteristic fire diameter	D* = [Q / (ρ_∞c_pT_∞√g)]^2/5	NIST FDS User’s Guide	FDS Mesh Size
Smoke control and tenability
Axisymmetric plume mass flow	m = 0.071 Q_c^1/3z^5/3 + 0.0018 Q_c, kg/s above the flame	NFPA 92	Atrium Smoke Exhaust
Smoke filling, steady fire	z/H = 1.11 − 0.28 ln[(t Q^1/3/H^4/3) / (A/H²)]	NFPA 92	Smoke Layer Descent
Stack effect	ΔP = 3460 (1/T_o − 1/T_i) h, Pa with T in K and h in m	NFPA 92	Stack Effect
Door opening force	F = F_dc + W A ΔP / [2 (W − d)], SI units	NFPA 92, NFPA 101	Door Opening Force
Visibility through smoke	S = K/σ, with K = 8 for light-emitting and 3 for light-reflecting signs	NFPA 92	Visibility in Smoke
Fractional effective dose	FED = Σ (dose received / dose that incapacitates), with 0.3 and 1.0 as criteria	ISO 13571	FED Tenability
Suppression, structural, egress and hazards
Clean agent quantity	W = (V/S) C/(100 − C) for halocarbons; X = 2.303 (V_s/S) log₁₀[100/(100 − C)] for inert gases	NFPA 2001	Clean Agent Quantity
SFRM thickness adjustment	h₂ = h₁ (W₁/D₁ + 0.6) / (W₂/D₂ + 0.6)	IBC 722.5	SFRM Thickness
Effective char depth	a_eff = 1.2 β_nt^0.813, with β_n = 1.5 in./hr and t in hours	AWC NDS Chapter 16	Char Depth
Hydraulic egress model	S = k (1 − a D), F_s = S D; exit time = first-person travel + N/F_c	Fruin, Pauls	Egress Time
Mixture flammable limit (Le Chatelier)	LFL_mix = 1 / Σ(y_i/LFL_i)	NFPA 69	Gas Mixture LFL
Point source radiation	q″ = χ_rQ / (4πR²)	NUREG-1805	Pool Fire Radiation
BLEVE fireball	D = 5.8 M^1/3, t = 0.45 M^1/3, m and s with M in kg (M < 30,000 kg)	CCPS	Fireball

Frequently Asked Questions

What safety margin should a sprinkler system have between demand and water supply?

NFPA 13 does not set one. The system demand, with the hose stream allowance added, has to fall at or below the water supply curve at the total flow. Many authorities having jurisdiction and some insurers ask for a cushion on top of that, often a fixed pressure such as 5 or 10 psi or a percentage of the available pressure, to cover seasonal and long-term changes in the supply. Confirm the requirement for the project before relying on a margin.

How is friction loss calculated in sprinkler piping?

NFPA 13 uses the Hazen-Williams formula, p = 4.52 Q^1.85 / (C^1.85 d^4.87), which gives the loss in psi per foot for a flow Q in gpm, a C-factor for the pipe material and condition, and the internal diameter d in inches. Fittings and valves are added as equivalent lengths of pipe. Where the fluid is not water at normal temperature, such as an antifreeze solution, the Darcy-Weisbach equation with the Colebrook friction factor is the more accurate method, and NFPA 13 requires it for some antifreeze systems.

How do you calculate the available flow from a hydrant flow test?

NFPA 291 projects the test to a lower residual pressure with Q_R = Q_F × (h_R/h_F)^0.54. Q_F is the flow measured during the test, h_F is the pressure drop during the test (static minus residual) and h_R is the pressure drop to the target residual, usually 20 psi. On N^1.85 graph paper the static point and the test point join in a straight supply line.

Can results from these calculators be used in a permit submittal?

They are engineering aids for sizing, checking and reviewing. Permit submittals usually need complete calculations prepared by the responsible designer, often in hydraulic calculation software, and signed or sealed as the jurisdiction requires. Each tool page lists its method, assumptions and sources so a reviewer can follow how a number was reached.

Are the calculators free, and is anything I enter stored?

They are free, with no account or download. Every calculation runs in your browser and nothing you enter is sent to DGA. A few tools can keep your inputs in your own browser so they are there when you come back.

Which code editions do the calculators follow?

Each calculator page names the standard it follows, and most list their references with the edition used. Adopted editions vary by state and city, so confirm what the authority having jurisdiction enforces. The Fire Code Cheat Sheet lists the building and fire code editions in force in the states DGA serves.

About These Tools

DGA Fire Protection Engineering maintains these calculators. Each one implements a published method: the NFPA standards, the building and fire codes, and public US government fire dynamics references. Each tool page names the standard, summarizes the method, lists the main assumptions and cites its sources. Everything runs in your browser: nothing you enter is sent to DGA or stored anywhere except, for tools that offer it, your own browser.

Engineering aid only, provided as is and without warranty. Results depend on the inputs and on the simplifying assumptions of the method summarized on each tool page, and DGA has not verified them for your application. They do not replace code-required design, testing or review by the licensed engineer responsible for the project. Use of the tools is subject to the Terms of Use.