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Fire Flow Calculator

Created by Tobiasz Szlęk
Reviewed by Dominik Czernia, PhD and Steven Wooding
Based on research by
James P. Smith Calculating Fire Flow; Firehouse; June 1, 1996
Last updated: Jan 18, 2024

Our fire flow calculator is an efficient tool for determining the required fire flow (RFF) for suppressing and controlling fire.

If you're looking to determine the required fire flow for a particular structure or incident, you're in the right place. Whether you're a firefighter, a fire protection engineer, or simply interested in fire safety, this tool will assist you in your fire flow calculations.

Be sure to check out our flow rate calculator or, a more specific tool, the pipe flow calculator, to learn more about this metric in fluid mechanics!

What is fire flow?

Fire flow refers to the amount of water required to suppress or control a fire effectively. It represents the flow rate of water, typically measured in gallons per minute (GPM), that needs to be delivered to the fire scene.

How to calculate fire flow

Effective firefighting requires courage, skills, and a good understanding of fundamental calculations such as fire flow. Essential in assessing the volume of water necessary to extinguish a fire, fire flow calculation plays a critical role in fire suppression. Let's delve deeper into what fire flow is, why it's vital, and how to compute it accurately. We have chosen the National Fire Academy (NFA) method to introduce the topic and the IOWA fire flow formula as a supplementary method, but there are at least five other recognized ways of calculating fire flow.

To find the required fire flow RFF\mathrm{RFF} in gallons per minute for an area on fire with the NFA method, you need to:

  1. Multiply length LL and width WW of the area (both in feet).
  2. Divide the result by 3.
  3. Multiply by number of floors FF that are on fire.
RFF=L×W3×F\mathrm{RFF} = \frac{L \times W}{3} \times F

Additionally, to increase the result's precision, you can specify how much percent of the building is burning and how many interior and exterior objects are exposed to fire. The former is a simple fire flow percentage calculation, e.g., 50% fire involvement results in half of RFF\mathrm{RFF}, while the number of exposures adds an additional 25% to the RFF\mathrm{RFF}.

You can use our fire flow calculator to determine the necessary fire flow, taking into account all the mentioned factors. Be sure to check its advanced mode and see the gallons per minute calculator if you want to learn more about this unit.

🔎 Interior exposures are additional floors in the building (up to 5 exposures) that are exposed to fire. Usually, these are floors above the burning floor (fire "climbs" upwards). Exterior exposures include surrounding structures, such as other buildings, next to the burning object.

The role of fire flow in fire suppression

Fire flow calculation is integral to the efficiency of firefighting operations. It allows firefighters to develop a strategic attack plan based on an estimate of the size of the fire and the resources at their disposal. Moreover, it helps prevent the wastage of resources and minimizes potential damage caused by excessive water usage.

IOWA and NFA fire flow formulae

Two common formulae for fire flow calculation are the National Fire Academy (NFA) method and the Iowa State University (ISU) method. We already explained the former when we introduced the needed fire flow calculator in previous sections. You can find more information on the NFA fire flow formula on the Firehouse website.

Now, let's focus on the IOWA fire flow formula (ISU method), which is as follows:

RFF=V100=L×W×H100\mathrm{RFF} = \frac{V}{100} = \frac{L \times W \times H}{100}


  • RFF\mathrm{RFF} — Required fire flow in gallons per minute (GPM);
  • VV — Volume of the building on fire; and
  • LL, WW, HH — Length, width, and height of the building, respectively, allowing us to find VV from the volume of a rectangular prism formula.

Example: fire flow test

Let's use an example to present how to use the needed fire flow calculator. Let's assume we want to test the fire flow for one of the single-story buildings in your area. You need to:

  • Determine the length of the building: let's say it's 20 ft\mathrm{20 \ ft}.
  • Determine its width: for this example width is also 20 ft\mathrm{20 \ ft}.
  • Calculate the fire flow using the NFA formula:
RFF=20×203133 GPM\qquad \begin{split} \mathrm{RFF} &= \frac{20 \times 20}{3}\\[1em] &\approx 133 \mathrm{ \ GPM} \end{split}

Remember that these calculations only provide an estimate. You can increase the precision by considering additional factors available in our fire flow calculator's advanced mode. Still, the actual fire flow needed may vary based on various factors, such as the nature of the fire, wind conditions, and materials involved in the fire.


What is the maximum fire flow?

The maximum required fire flow for a single fire event is 12,000 GPM (45,500 L/min).

The term "maximum fire flow" refers to the highest amount of water, measured in gallons per minute (GPM), that can be supplied by a water distribution system or a specific source during firefighting operations.

What GPM is required for a fire hydrant?

A fire hydrant's required flow rate typically ranges between 500 to 1,500 gallons per minute (GPM). However, the exact GPM can vary based on local regulations, the area's fire risks, and specific infrastructure capabilities.

How do I calculate required fire flow?

To find the required fire flow (RFF) for a burning building:

  1. Determine the length of the building on fire.

  2. Determine its width.

  3. Multiply the length by width and divide by 3.

  4. Multiply the results by the number of floors on fire. The fire flow formula is:

    RFF = length × width × no. floors / 3

    but can be extended by taking into account what part of the building is on fire and if additional objects are exposed to fire.

What is a required fire flow for the area 6 by 4 feet?

The required fire flow (RFF) is 8 GPM or 30 liters per minute for a single-level area with a 6×4 sq ft dimension. You can find it using the fire flow formula assuming that the number of floors on fire is one:

RFF = length × width × no. floors / 3

Tobiasz Szlęk
Method and building dimensions
National Fire Academy
Building length
Building width
Additional information
Fire involvement
No. burning floors
Required fire flow (RFF)
US gal/min
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