How much foam concentrate do I need?

Foam concentrate needed (gallons) = Tank size (gallons) × (concentration% ÷ 100). For example, a 500-gallon tank with 3% AFFF needs 15 gallons of concentrate and 485 gallons of water. Use the calculator above to get instant results for any foam type and tank size.

What is the difference between 1%, 3%, and 6% foam concentrate?

The percentage refers to how much concentrate is mixed into the finished foam solution. 1% means 1 part concentrate to 99 parts water. 3% is the most common field ratio for AFFF on hydrocarbon fuels. 6% is used for fixed suppression systems or high-hazard polar solvent fires with AR-AFFF. Class A foam typically runs at 0.1%–1% depending on application method.

What is the NFPA 11 minimum application rate for foam?

NFPA 11 specifies minimum application rates by foam type and hazard. For AFFF on hydrocarbon spill fires, the minimum is 0.10 GPM per square foot of fire area. For Class A foam (aspirated), typical rates are 0.05–0.10 GPM/ft². CAFS systems can achieve equivalent suppression at 0.04 GPM/ft² equivalent due to the foam expansion ratio. Always verify with your department SOP and current NFPA 11.

What is CAFS and how is it different from standard foam?

CAFS (Compressed Air Foam System) injects compressed air into a Class A foam solution before it leaves the nozzle, creating a very lightweight, stable foam that sticks to surfaces. Unlike standard aspirated foam, CAFS requires far less water (typically 0.1%–0.5% concentrate) and can extend tank life significantly. It excels in wildland-urban interface and overhaul operations but is not suitable for Class B (flammable liquid) fires.

Can I use Class A foam on Class B fires?

No. Class A foam is not rated for flammable or combustible liquid (Class B) fires. It does not form the vapor-suppressing aqueous film that AFFF or AR-AFFF provides. For hydrocarbon fires use AFFF; for polar solvents (alcohol, acetone, ethanol) use AR-AFFF. Using the wrong foam type on a Class B fire can be dangerous.

How long does foam application take?

Application time depends on total solution volume and your nozzle flow rate. Time (minutes) = Total solution (gallons) ÷ Flow rate (GPM). A 500-gallon tank flowing at 100 GPM lasts 5 minutes. Enter your flow rate in the calculator to see application time and plan relay or tanker operations accordingly.

How much foam concentrate do I need?

Foam concentrate needed (gallons) = Tank size (gallons) × (concentration% ÷ 100). For example, a 500-gallon tank with 3% AFFF needs 15 gallons of concentrate and 485 gallons of water. Use the calculator above to get instant results for any foam type and tank size.

What is the difference between 1%, 3%, and 6% foam concentrate?

The percentage refers to how much concentrate is mixed into the finished foam solution. 1% means 1 part concentrate to 99 parts water. 3% is the most common field ratio for AFFF on hydrocarbon fuels. 6% is used for fixed suppression systems or high-hazard polar solvent fires with AR-AFFF. Class A foam typically runs at 0.1%–1% depending on application method.

What is the NFPA 11 minimum application rate for foam?

NFPA 11 specifies minimum application rates by foam type and hazard. For AFFF on hydrocarbon spill fires, the minimum is 0.10 GPM per square foot of fire area. For Class A foam (aspirated), typical rates are 0.05–0.10 GPM/ft². CAFS systems can achieve equivalent suppression at 0.04 GPM/ft² equivalent due to the foam expansion ratio. Always verify with your department SOP and current NFPA 11.

What is CAFS and how is it different from standard foam?

CAFS (Compressed Air Foam System) injects compressed air into a Class A foam solution before it leaves the nozzle, creating a very lightweight, stable foam that sticks to surfaces. Unlike standard aspirated foam, CAFS requires far less water (typically 0.1%–0.5% concentrate) and can extend tank life significantly. It excels in wildland-urban interface and overhaul operations but is not suitable for Class B (flammable liquid) fires.

Can I use Class A foam on Class B fires?

No. Class A foam is not rated for flammable or combustible liquid (Class B) fires. It does not form the vapor-suppressing aqueous film that AFFF or AR-AFFF provides. For hydrocarbon fires use AFFF; for polar solvents (alcohol, acetone, ethanol) use AR-AFFF. Using the wrong foam type on a Class B fire can be dangerous.

How long does foam application take?

Application time depends on total solution volume and your nozzle flow rate. Time (minutes) = Total solution (gallons) ÷ Flow rate (GPM). A 500-gallon tank flowing at 100 GPM lasts 5 minutes. Enter your flow rate in the calculator to see application time and plan relay or tanker operations accordingly.

Firefighter Foam Calculator — Class A, B & CAFS

Q: How do I calculate how many tank loads I need?

Tank loads needed = Total foam solution required (gallons) ÷ Apparatus tank size (gallons). Total solution = Fire area (ft²) × Application rate (GPM/ft²) × Application time (minutes). The calculator above computes this automatically when you enter the fire area and your tank size.

Foam Solution Calculator

Results update instantly. All calculations follow NFPA 11 guidelines.

Foam concentrate
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Water needed

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Application time

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at selected GPM

Mix ratio

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conc. : water

Full breakdown

Foam type—

Concentration—

Tank size—

Concentrate per tank—

Water per tank—

Flow rate—

Tank duration at flow rate—

Training/planning use only. Always follow department SOP/SOG and consult current NFPA 11 and ERG for incident operations. Editorial policy

Foam Types for Firefighters

Firefighting foam is classified by the fuel type it suppresses. Class A foam is used on ordinary combustibles (wood, vegetation, structure fires). Class B foam (AFFF and AR-AFFF) suppresses flammable and combustible liquid fires. CAFS uses compressed air to produce a lightweight, adhesive foam for wildland and overhaul operations.

🏠

Class A Foam

Structure fires, wildland-urban interface (WUI), exposure protection

Typical ratios: 0.1%, 0.3%, 0.5%, 1.0%

NFPA 11 min rate: 0.06 GPM/ft²

⛽

Class B — AFFF

Hydrocarbon fuels (gasoline, diesel, jet fuel)

Typical ratios: 1%, 3%, 6%

NFPA 11 min rate: 0.1 GPM/ft²

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Class B — AR-AFFF

Alcohol-resistant; polar solvents (ethanol, methanol, ketones)

Typical ratios: 3%, 6%

NFPA 11 min rate: 0.1 GPM/ft²

💨

CAFS — Compressed Air Foam

Wildland, structure knockdown & overhaul; Class A concentrate

Typical ratios: 0.1%, 0.3%, 0.5%

NFPA 11 min rate: 0.04 GPM/ft²

Understanding Concentration Ratios

The concentration percentage tells you how much foam concentrate goes into each gallon of finished solution:

Concentration	Concentrate / 100 gal	Water / 100 gal	Typical use
0.1%	0.1 gal	99.9 gal	CAFS wet foam, wildland
0.3%	0.3 gal	99.7 gal	Class A structure, CAFS standard
1%	1 gal	99 gal	AFFF on hydrocarbon (low-ratio)
3%	3 gal	97 gal	AFFF/AR-AFFF standard
6%	6 gal	94 gal	Fixed systems, polar solvents

Formula: Concentrate (gal) = Tank size (gal) × (concentration ÷ 100). For a 500-gal tank at 3%: 500 × 0.03 = 15 gallons concentrate, 485 gallons water.

NFPA 11 Application Rates

NFPA 11 specifies minimum foam application rates based on foam type and hazard class. Using the calculator's area input, you can determine total solution volume and required tank loads.

Foam type	NFPA 11 min. rate	Application method	Notes
Class A	0.05–0.10 GPM/ft²	Aspirated or CAFS	Varies by fuel depth and exposure
AFFF (Class B)	0.10 GPM/ft²	Aspirated or non-aspirated	Hydrocarbon spill fires (NFPA 11 Table 5.3.2)
AR-AFFF on hydrocarbons	0.10 GPM/ft²	Aspirated	Same rate as AFFF
AR-AFFF on polar solvents	0.10 GPM/ft²	Aspirated only	6% concentration required for polar solvents
CAFS equivalent	≈ 0.04 GPM/ft²	Compressed air	Higher expansion ratio extends coverage

Always verify with current NFPA 11 and your department SOP. Application rates for fixed systems, subsurface injection, and high-expansion foam differ significantly.

How to Use This Foam Calculator

Select foam type

Choose Class A, AFFF, AR-AFFF, or CAFS. The NFPA 11 application rate and available concentration ratios update automatically.

Choose concentration ratio

Select from the pre-set pills (e.g. 3% for AFFF) or enter a custom percentage. Your department SOP or the foam manufacturer's datasheet will specify the correct ratio for your foam.

Enter tank size and flow rate

Enter your apparatus tank capacity in gallons and your nozzle or master stream flow rate in GPM. The calculator instantly shows concentrate amount, water needed, and application time.

Add fire area for tank planning

Enter the estimated fire or spill area in square feet to calculate total solution required, tank loads needed, and whether your on-scene resources are sufficient.

Set available tanks

Enter the number of tank loads available (pre-fill, tender, etc.) to see coverage vs. demand and get an immediate gap warning if supply is insufficient.

CAFS Operations — What's Different

Compressed Air Foam Systems (CAFS) inject compressed air into a Class A foam solution before it leaves the pump, creating a very stable, lightweight foam blanket.

CAFS advantages

Dramatically reduces water use — effective at 0.1–0.5% concentrate
Foam sticks to vertical surfaces for exposure protection
Extended tank life — same tank covers more area
Lighter hose loads (air replaces water volume)
Excellent for wildland-urban interface and overhaul

CAFS limitations

Never use CAFS on Class B fires — not rated for flammable liquids
Requires properly calibrated CAFS system
Consistency depends on air-to-solution ratio (wet/dry foam)
Not all nozzles are CAFS-compatible
Special training required per department SOP

Foam Calculator FAQ

Foam concentrate (gallons) = Tank size (gallons) × (concentration% ÷ 100). For a 500-gallon tank at 3%: 500 × 0.03 = 15 gallons of concentrate and 485 gallons of water. Use the calculator above to instantly compute any combination.

AFFF (Aqueous Film-Forming Foam) is designed for hydrocarbon fuels like gasoline, diesel, and jet fuel. AR-AFFF (Alcohol-Resistant AFFF) works on both hydrocarbons AND polar solvents like ethanol, methanol, acetone, and other water-miscible fuels. If you face a polar solvent fire with regular AFFF, the foam breaks down immediately — always use AR-AFFF on unknown or mixed fuels.

No. Class A foam is not rated for Class B (flammable liquid) fires. It does not form the aqueous vapor-suppressing film that AFFF provides. Using Class A foam on a gasoline fire is ineffective and potentially dangerous. Always use AFFF or AR-AFFF on hydrocarbon and polar solvent fires.

For AFFF on hydrocarbon spill fires, NFPA 11 requires a minimum of 0.10 GPM per square foot of fire area. Class A foam (aspirated) typically requires 0.05–0.10 GPM/ft². CAFS achieves equivalent suppression at approximately 0.04 GPM/ft² due to the higher foam expansion ratio. Always confirm with your department SOP and current edition of NFPA 11.

Total solution needed (gal) = Fire area (ft²) × Application rate (GPM/ft²) × Application time (min). Tank loads = Total solution ÷ Apparatus tank size. Enter your fire area into the calculator above and it computes this automatically, including a warning if your available tanks are insufficient.

Application time (minutes) = Tank size (gallons) ÷ Flow rate (GPM). A 500-gallon tank at 100 GPM lasts 5 minutes. At 50 GPM, it lasts 10 minutes. Enter your flow rate in the calculator to see duration. For extended operations, plan tanker shuttle or hydrant supply before tank runs dry.

No. This tool is designed for mobile apparatus and fireground planning only. Fixed suppression system design (hangar systems, loading rack systems, tank farms) requires a licensed fire protection engineer and full compliance with NFPA 11, NFPA 30, and relevant codes. Do not use this tool for system design or acceptance testing.

Disclaimer: This calculator is for training and pre-incident planning only. For live incidents, always follow your department SOP/SOG and consult the current NFPA 11 and product manufacturer's datasheet. Editorial policy · Our authors

Foam Solution Calculator

Foam Types for Firefighters

Class A Foam

Class B — AFFF

Class B — AR-AFFF

CAFS — Compressed Air Foam

Understanding Concentration Ratios

NFPA 11 Application Rates

How to Use This Foam Calculator

CAFS Operations — What's Different

CAFS advantages

CAFS limitations

Foam Calculator FAQ

How much foam concentrate do I need?

What is the difference between AFFF and AR-AFFF?

Can I use Class A foam on a gasoline fire?

What is the NFPA 11 minimum application rate?

How do I calculate how many tanks I need?

How long will my tank last when flowing foam?

Is this calculator suitable for fixed suppression system design?

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