Enter the length, width, and height of an area of a building that is on fire into the calculator to determine the required fire flow.
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Fire Flow Formula
The following two formulas are the two most common formulas used to calculate fire flow.
RFF = V / 100 (ISU Method)
RFF = L*W / 3 (NFA Method)
- Where RFF is the required fire flow (GPM)
- V is the volume (square feet)
- L is the length (feet)
- W is the width
To calculate fire flow, multiply the length by the width, then divide by 3.
Fire Flow Definition
What is fire flow? Fire flow is a measure of the total rate of water flow required to suppress a fire. Fire flow is most often expressed in gallons per minute. It’s often used as a rough estimate as opposed to an exact measure.
Example Problem
How to calculate fire flow?
- First, determine the length of the area on fire.
For this example, the length is 10 ft.
- Next, determine the width of the area.
For this example, the width is 20 ft.
- Next, determine the height.
In this problem the height is 8 ft.
- Finally, calculate the fire flow.
Using the formula: 10*20*8/3 = 16 GPM

