Propane Tank Calculator
Propane left in pounds and gallons plus grill burn time from weights.
What it does
Grill gauges guess while scales tell the truth. Weigh the tank, subtract the TW tare stamped on its collar, and the difference is propane: 30 lb on a 17 lb tank leaves 13 lb. The tool above converts that into gallons and grill hours at any burner rating.
The default runs a mid cook tank at a 30,000 BTU grill. Thirteen pounds divide by 4.24 into 3.07 gallons, times 91,452 BTU per gallon is about 280,000 BTU, and at full blast that burns 9 hours 21 minutes. Real cooks with cycling burners stretch far past the full blast figure.
Two federal references anchor the constants. The Energy Information Administration tables propane at 91,452 BTU per gallon, and EPA compilations carry the matching weights and conversion factors for the fuel. A gallon of liquid propane weighs 4.24 lb at standard conditions, so a 20 lb cylinder carries near 4.7 gallons.
The 80% fill rule explains half empty readings. Liquid propane expands with heat, so tanks legally stop at four fifths to leave vapor room; a 20 lb tank is full at 20 lb of fuel, not at the brim. Cold weather shrinks gauge readings without changing the energy inside.
How to use
- Weigh the tank on a bathroom scale.
- Read the TW tare stamped on the collar.
- Type both weights into the tool.
- Type the grill BTU rating with burners on.
- Read fuel first, grill hours beside it.
Formula
- tare (lb)
- Empty tank weight stamped TW.
- 4.24
- Pounds per gallon of liquid propane.
- 91,452
- BTU per gallon (EIA).
Full blast math; cycling burners sip far less per hour. US grill tanks quote pounds and BTU; metric readouts print beside imperial results.
Worked example
Example: 30 lb scale, 17 lb tare
Defaults: scale 30 lb, tare 17 lb, burner 30,000 BTU/h.
- Fuel: 30 minus 17 = 13 lb (5.9 kg).
- Gallons: 13 / 4.24 = 3.07 gal (11.6 L).
- Energy: 3.07 x 91,452 = about 280,000 BTU.
- Hours: 280,000 / 30,000 = 9.35 h = 9 h 21 min.
- Tool shows 13 lb (5.9 kg), 3.07 gal (11.6 L), 9 h 21 min.
Reference table
| Burner | Fuel | Full blast time |
|---|---|---|
| 15,000 BTU/h | 4.72 gal | 28 h 46 min |
| 30,000 BTU/h | 4.72 gal | 14 h 23 min |
| 60,000 BTU/h | 4.72 gal | 7 h 11 min |
Limits
- Full blast rating; real cooks cycle lower.
- Scale and tare accuracy set everything.
- Temperature swings move gauges, not energy.
- US cylinder conventions assumed.
Common mistakes
- Reading percent gauges as pounds.
- Forgetting to subtract tare weight.
- Refilling past 80% deliberate headroom.
- Trusting exchange tanks as truly full.
- Sizing cooks at nameplate instead of cycling use.
Try it yourself
Quick checks. Answers sit tucked under each question.
37 lb scale, 17 tare, 50,000 BTU?
20 lb (9.1 kg), 4.72 gal (17.9 L), 8 h 38 min.
24 lb scale, 17 tare, 15,000 BTU?
7 lb (3.2 kg), 1.65 gal (6.2 L), 10 h 4 min.
Full 20 lb tank at 30,000 BTU?
4.72 gal holds 431,375 BTU, 14 h 23 min.
Questions
How much propane is left?
Scale minus TW tare: 30 minus 17 is 13 lb here.
Gallons in 13 lb?
13 / 4.24 = 3.07 gal.
How long will it grill?
Gallons x 91,452 / BTU rating; 9 h 21 min here.
What is TW?
Tare weight: the empty tank stamping on the collar.
Why never 100% full?
Liquid expands with heat; 80% leaves vapor room.
Cold shrank my gauge?
Volume shrinks but energy stays; weigh to be sure.