Estimate how long usable propane lasts at your burn rate. Enter usable pounds (weigh or nameplate remaining) and burn lb/hr — optional daily stove hours converts hours to days. Planning aid.
Use this when you know usable propane mass in pounds and a burn rate in lb/hr (from a log or from appliance BTU/hr ÷ 21600). The calculator returns runtime hours; optional stove hours per day converts that into approximate days.
Weigh tanks (tare on the collar) and enter remaining usable propane — not the steel cylinder weight and not a full “20 lb” nameplate if the bottle is half empty. Optional BTU/hr overrides the burn field using ≈21,600 BTU per pound of propane.
This is a consumption estimate — not a gauge substitute, not locker ventilation design (see propane locker vent area), and not a fire-safety procedure.
Runtime hours equal usable pounds divided by burn rate in lb/hr. If daily stove (or appliance) hours are greater than zero, days ≈ hours ÷ hours_per_day. If appliance BTU/hr is entered and positive, burn rate is replaced by BTU/hr ÷ 21600.
hours = usable_lb ÷ burn_lb_per_hr
days ≈ hours ÷ stove_h_per_day (optional)
burn ≈ BTU_hr ÷ 21600 (optional override)
Real appliances cycle below continuous BTU; a logged lb/hr from weigh-ins beats a nameplate BTU conversion. Propane refrigeration can dominate — do not use a cooktop-only burn for a fridge-equipped boat.
| Usable lb | Burn lb/hr | h/day | BTU/hr | Hours | Days |
|---|---|---|---|---|---|
| 10 | 0.25 | 1.5 | — | 40.0 | 26.7 |
| 20 | 0.40 | 2.0 | — | 50.0 | 25.0 |
| 10 | (from BTU) | — | 5400 | 40.0 | — |
| 15 | (from BTU) | 1.5 | 10800 | 30.0 | 20.0 |
| 5 | 0.20 | 1.0 | — | 25.0 | 25.0 |
Rows were computed independently (hours = lb/burn, days = hours/hpd, burn = BTU/21600 when BTU set) and match this page. Default example: 10 lb ÷ 0.25 lb/hr → 40.0 h · ≈ 26.7 days at 1.5 h/day. BTU rows: 5400÷21600 = 0.25 lb/hr; 10800÷21600 = 0.50 lb/hr.
Units: Pounds of usable propane; burn in lb/hr; optional BTU/hr with the 21,600 BTU/lb planning figure.
Where the formula fails: unknown remaining mass (guessing from a float gauge), mixing butane, and multi-appliance duty that you have not summed into one burn rate. Locker vent area and regulator capacity are out of scope.
Not a substitute: planning aid only — not a tank gauge, not ABYC locker guidance, and not fire-safety or leak-test procedure.
Nameplate “20 lb” is full propane mass. Enter remaining usable pounds after weighing — not the steel cylinder weight.
Common planning figure ≈21,600 BTU per pound of propane. Real appliances cycle below continuous BTU; logged lb/hr is better.
Propane fridges can dominate burn. Use a measured or manufacturer continuous rate, not cooktop-only defaults.
Yes. When optional BTU/hr is positive, the script sets burn = BTU ÷ 21600 and uses that for hours (and days).
Enter the usable pounds you will draw from (one bottle or the sum if you intentionally run them as a pool). The model is a single usable mass ÷ burn.