# Fire Flow Calculator

URL: https://speedycalculator.com/calculators/construction/fire-flow/
Last updated: 2026-10-25

> The fire flow calculator estimates the water flow needed to fight a fire in a building with the National Fire Academy (NFA) quick formula and the Iowa State formula, in gallons per minute and litres per minute.

## Inputs

- Length (ft, m, in, yd, cm)
- Width (ft, m, in, yd, cm)
- Ceiling height (ft, m, in, yd, cm)
- Floors involved
- Fire involvement

## Results

- NFA needed fire flow
- Iowa formula flow
- 1¾ in hand lines at 150 gpm (NFA)

## Formula

```
NFA: needed fire flow (gpm) = length × width ÷ 3 × % involvement × floors involved
Iowa: flow (gpm) = room volume (ft³) ÷ 100
```

## Explanation

Fire officers use quick fire-flow formulas on scene and in pre-incident planning to decide how many hose lines and how much water supply a fire needs. The NFA formula assumes 1 gpm for every 3 ft² of fire area; the Iowa formula, developed for enclosed spaces, divides the volume by 100. Both are estimates for tactics, not for designing a water system.

### How to use the Fire Flow Calculator

- **Length**
- **Width**
- **Ceiling height**
- **Floors involved**
- **Fire involvement**

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Enter the building or fire-area length and width, ceiling height, the number of floors involved and the percentage of the area on fire.

### Tips for an accurate estimate

- Measure inside dimensions of tanks and pools – wall thickness can change the volume noticeably.
- Use the average depth for pools with a sloping floor.
- Remember the weight: water weighs about 8.34 lb per US gallon (1 kg per litre), so large volumes need solid support.
- Check whether a figure is in US gallons, imperial gallons or litres before ordering chemicals or equipment.

### Common mistakes to avoid

- Using wall height instead of water depth for above-ground pools.
- Assuming a horizontal tank's volume is proportional to the liquid level – it is not.
- Mixing up flow units such as GPM, GPH and litres per minute.

### Inputs explained

FieldWhat to enterLengthUnits: ft, m, in, yd, cmWidthUnits: ft, m, in, yd, cmCeiling heightUnits: ft, m, in, yd, cmFloors involvedA numberFire involvementChoose one: 25%, 50%, 75%, 100%

### What each result means

- **NFA needed fire flow** = ([Length]×[Width]÷0.09290304)÷3×[Fire involvement]÷100×[Floors involved]×6.30901964e-5
- **Iowa formula flow** = [Length]×[Width]×[Ceiling height]×[Floors involved]÷0.028316846592÷100×6.30901964e-5
- **1¾ in hand lines at 150 gpm (NFA)** = ceil([NFA needed fire flow]÷(150×6.30901964e-5) - 0.000001)

### Example values

How the main result changes when **Length** changes and everything else stays at the example values above:

Length (ft)NFA needed fire flow (gpm)304004560060800751,000901,2001201,600

## Worked example

Inputs — Length: 60 ft; Width: 40 ft; Ceiling height: 10 ft; Floors involved: 1; Fire involvement: 100%.

Results — **NFA needed fire flow = 800 gpm**; Iowa formula flow = 240 gpm; 1¾ in hand lines at 150 gpm (NFA) = 6.

## FAQ

**What is the NFA fire flow formula?**
Needed fire flow (gpm) = (length × width) ÷ 3, multiplied by the percentage of involvement.

**What is the Iowa formula?**
Gallons per minute = volume of the space (ft³) ÷ 100, applied over 30 seconds.

**How much does a hand line flow?**
A 1¾ in attack line typically flows 150–185 gpm; a 2½ in line about 250–300 gpm.

**What formula does the Fire Flow Calculator use?**
NFA: needed fire flow (gpm) = length × width ÷ 3 × % involvement × floors involved.


## Sources

- [U.S. Fire Administration – National Fire Academy fire flow formula](https://www.usfa.fema.gov/)