How do you calculate foam concentrate?

Multiply flow (gpm) by time (min) to get total solution, then multiply by the proportioning percentage. 150 gpm x 10 min x 3% = 45 gallons of concentrate.

What is the difference between 3% and 6% foam?

3% foam uses 3 gallons of concentrate per 100 gallons of solution; 6% uses 6. For the same operation, 6% foam consumes twice the concentrate of 3%.

How much reserve foam should I carry?

This calculator gives the minimum for the time you enter. Most departments plan reserve concentrate beyond the initial estimate; follow your SOPs and the fuel involved.

Does Class A foam use the same math?

Yes. The formula is identical, just at lower percentages (typically 0.1% to 1%), so Class A uses far less concentrate for the same flow and time.

Foam concentrate calculator

Work out how much foam concentrate you need for an operation — from the flow rate, duration, and proportioning percentage. For Class A and Class B foam planning.

Flow rate (gpm)

Duration (min)

Concentration

Foam concentrate needed — gal

Concentrate is the proportioning percentage of the total foam solution produced. The rest is water. Always carry reserve concentrate — this is the minimum for the time entered.

How foam concentrate is calculated

First find the total foam solution you will produce, then take the proportioning percentage of it:

Solution (gal) = Flow (gpm) × Time (min)
Concentrate (gal) = Solution × (% / 100)

For example, a 3% proportioner uses 3 gallons of concentrate for every 100 gallons of finished foam solution; the other 97 gallons are water.

Common proportioning rates

Foam type	Typical %
Class A (structural/wildland)	0.1–1%
Class B AFFF / AR-AFFF	1% or 3%
Class B (older / protein)	3% or 6%

Worked example

A 150 gpm foam line flowing for 10 minutes at 3%:

Solution = 150 × 10 = 1500 gal
Concentrate = 1500 × 0.03 = 45 gal

Frequently asked questions

How do you calculate foam concentrate?: Multiply flow (gpm) by time (min) to get total solution, then multiply by the proportioning percentage. 150 gpm × 10 min × 3% = 45 gallons of concentrate.
What is the difference between 3% and 6% foam?: 3% foam uses 3 gallons of concentrate per 100 gallons of solution; 6% uses 6. For the same operation, 6% foam consumes twice the concentrate of 3%.
How much reserve foam should I carry?: This calculator gives the minimum for the time you enter. Most departments plan reserve concentrate beyond the initial estimate; follow your SOPs and the fuel/hazard involved.
Does Class A foam use the same math?: Yes — the formula is identical, just at lower percentages (typically 0.1% to 1%), so Class A uses far less concentrate for the same flow and time.

Worked Example

Class A, wildland-urban interface: a 95 GPM line through an eductor set at 0.3% for a 20-minute operation. Water used: 95 × 20 = 1,900 gal. Concentrate: 1,900 × 0.003 = 5.7 gallons — call it two 5-gallon pails with reserve.

Class B, fuel spill: 150 GPM at 3% for 15 minutes: 2,250 gal of water × 0.03 = 67.5 gallons of concentrate — nearly fourteen pails.

That order-of-magnitude difference is the lesson: Class B operations consume concentrate far faster than most departments carry. Run the math for your foam cell before the incident, not during it.

Foam math under pressure is where operations slip. Drill it.

PumpForge includes foam operations among its evolutions, scoring proportioning and delivery on a realistic panel — so the math is automatic when it counts.

Explore PumpForge →

For training and estimation; always verify against your foam product, proportioning equipment, and SOPs. Related tools: water supply duration, required fire flow, and pump discharge pressure. Foam proportioning is JPR §5.2.3 in NFPA 1002.