FireOpsCalcFire Engine Tank Duration Calculator
How long will your apparatus tank water last? Enter tank size and total fire flow to estimate working time, time to empty, usable water, and reserve.
Tank and flow inputs
Training/reference aid only. Follow department SOPs, instructor direction, manufacturer data, and local conditions.
Tank duration results
How to calculate fire engine tank duration
Tank duration is the estimated time an engine can supply the selected fire flow using onboard water. A simple starting calculation is available gallons ÷ total GPM. This tool also lets you reduce the tank to a realistic usable-water percentage and preserve a desired reserve before calculating working time.
Example: 750-gallon tank at 185 GPM
With a 750-gallon tank, 90% usable water, and a 100-gallon reserve, approximately 575 gallons are available for working fire flow. At 185 GPM, that is about 3.1 minutes before reaching the selected reserve. Use the calculator above for your apparatus and current flow.
What changes tank time?
- Tank size: larger onboard tanks provide more time at the same flow.
- Total GPM: multiple lines, larger nozzles, or master streams shorten tank duration quickly.
- Usable water: apparatus plumbing, grade, and operations can affect how much water is practically available.
- Reserve: setting a reserve creates an earlier operational cue for establishing a sustained water supply.
Fire engine tank duration questions
How long does a 500-gallon fire engine tank last?
At 150 GPM, 500 gallons is about 3 minutes 20 seconds if every gallon were usable. At 200 GPM it is about 2 minutes 30 seconds. A reserve or reduced usable percentage shortens working time.
How long does a 750-gallon tank last at 150 GPM?
A theoretical 750 gallons at 150 GPM lasts 5 minutes. Operational working time may be shorter when preserving a reserve or accounting for unusable water.
How do multiple hoselines affect tank duration?
Add the GPM of all flowing lines and appliances, then divide available tank water by that total flow. For example, two 150-GPM lines create a 300-GPM total fire flow.
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