Fire Flow Calculator

Fire safety isn’t a guessing game. When you need to know how much water a building requires during a fire, you want clear answers fast. That’s why we built this Fire Flow Calculator. It’s simple, accurate, and works for both GPM (gallons per minute) and L/min. You’ll get results in seconds, without digging through complex charts.

What is Fire Flow?

Fire flow is the amount of water needed to control a fire in a specific building. It’s usually measured in GPM or L/min. The number depends on the building’s size, construction, contents, and nearby exposures. The right fire flow helps firefighters control flames before they spread.

The ISO Fire Flow Formula

The calculator uses the ISO Needed Fire Flow method. It’s trusted by fire safety pros worldwide.

Formula:

Fire Flow (gpm) = 18 × F × √A × O × [1 + (X + P)]

Where:

• F = Construction factor
• A = Effective area in ft²
• O = Occupancy factor
• X = Exposure factor
• P = Communication factor

If you enter metric values, the calculator converts them to feet² and gives results in liters per minute.

How to Use the Fire Flow Calculator

It’s as easy as filling a few boxes:

1. Enter the building’s effective area.
2. Select construction and occupancy factors.
3. Add any exposure or communication values.
4. Choose your unit system (Imperial or Metric).
5. If the building has sprinklers, set a reduction.
6. Hit “Calculate” and see your fire flow instantly.

For example:

A 3,600 ft² building, F=1.0, O=1.0, X=0.25, P=0.10, and 50% sprinkler reduction will give you 729 gpm.

Why Use This Calculator?

It removes guesswork. Many people use paper worksheets or spreadsheets for this, but that takes time. This tool applies the ISO formula instantly, does the conversions, and even shows step-by-step math. You’ll know exactly how the number was found.

Final Verdict

If you’re in fire safety, construction, or municipal planning, this Fire Flow Calculator will save you time. It’s quick, accurate, and uses the real ISO fire flow formula. Whether you’re working on a hydrant test, a code review, or a fire plan, you’ll have reliable numbers at your fingertips.

Common Questions

How do you calculate fire flow?

You multiply construction factor, square root of area, occupancy factor, and exposure adjustments using the ISO formula. The result is in GPM or L/min.

How many GPM is a fire flow?

It depends on the building. Small homes might need 500–1,000 GPM, while large warehouses could need several thousand.

What is the fire flow at 20 psi?

That refers to hydrant capacity testing. It’s about how much water a hydrant delivers at 20 psi residual pressure.

Can I use this for ISO fire flow?

Yes. It’s designed for ISO’s NFF calculation.