Work out propane tank duration instantly with clear inputs, formula shown and shareable results.
Propane carries about 91,500 BTU per gallon. Multiplying appliance input by the fraction of time it actually fires gives gallons per hour, and dividing the usable tank contents by that rate gives run time. Tanks are filled to 80 percent of water capacity to leave room for vapour expansion.
Burn rate
gal/h = input BTU/h x duty cycle / 91500
Duration
hours = tank gallons x fill fraction / burn rate
gal/h = input BTU/h x duty cycle / 91500. Propane carries about 91,500 BTU per gallon.
Liquid propane expands about 17 times more than water for the same temperature rise. The vapour space absorbs that expansion and prevents the relief valve lifting on a hot day.
This calculator takes 4 inputs: Tank water capacity, Fill level, Total appliance input, Average duty cycle. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.