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Propane Runtime Calculator
Pick your appliance and tank to see how many hours of propane you have. Presets use the Btu ratings published by Mr. Heater, Blackstone, Weber, Coleman and others; you can also enter any Btu rating from your appliance's label.
The formula
A propane appliance's Btu rating is how much fuel it burns per hour at full output. Divide the energy in your tank by that rating:
A full 20 lb tank holds 4.7 gallons, about 431,000 Btu. A 9,000 Btu heater burns 0.098 gallons per hour, which matches the 0.099 gallons per hour Mr. Heater publishes for the Portable Buddy on high. So a 20 lb tank lasts 431,000 ÷ 9,000 ≈ 48 hours.
Runtime cheat sheet (full tanks, burners on high)
| Appliance | Btu/hr | 1 lb cylinder | 20 lb tank | 100 lb tank |
|---|---|---|---|---|
| Mr. Heater Little Buddy | 3,800 | 5.8 h | 114 h | 568 h |
| Portable Buddy, low | 4,000 | 5.5 h | 108 h | 539 h |
| Portable Buddy, high | 9,000 | 2.5 h | 48 h | 240 h |
| Big Buddy, high | 18,000 | 1.2 h | 24 h | 120 h |
| Weber Q 1200 | 8,500 | 2.6 h | 51 h | 254 h |
| Coleman Classic stove, both burners | 20,000 | 1.1 h | 22 h | 108 h |
| Blackstone 22" griddle | 24,000 | 0.9 h | 18 h | 90 h |
| Weber Spirit II E-310 | 30,000 | – | 14 h | 72 h |
| Blackstone 28" griddle | 34,000 | – | 13 h | 63 h |
| Patio heater | 46,000 | – | 9.4 h | 47 h |
| Outland Firebowl | 58,000 | – | 7.4 h | 37 h |
| Blackstone 36" griddle | 60,000 | – | 7.2 h | 36 h |
Dashes mean the appliance isn't designed to run on a 1 lb cylinder. Times are pure fuel math; cold weather, wind and partly open valves all change real results.
Getting realistic numbers
Cooking appliances rarely run flat out. A griddle or grill is usually preheated on high and then cooked on medium or low. Set the output field to about 50–60% for typical cooking and you'll get a more realistic estimate. If you only light two of four burners, that is 50% too.
Thermostat-controlled appliances cycle. An RV furnace is rated at its full burn, but it switches on and off to hold the temperature. On a mild night it might run 25% of the time; on a night in the teens it can run 70% or more. Use the duty cycle field for this. Remember the furnace fan also draws on your 12-volt battery.
Small cylinders and cold weather don't mix. Propane has to boil off the liquid to feed the burner, and that cools the cylinder. Below freezing, a 1 lb cylinder on a high setting can lose pressure well before it is empty, which is one reason manufacturers' runtime claims are hard to match in winter. A 20 lb tank on a hose is far more stable.
Manufacturer claims vary. Mr. Heater advertises up to 3 hours on high for the Portable Buddy on a 1 lb cylinder; the fuel math gives about 2.5 hours using its own published burn rate. We show the math, and you can expect results somewhere around it.
Safety: what can and can't be used indoors
Only heaters specifically rated for indoor use, like the Mr. Heater Buddy series with its low-oxygen and tip-over shutoffs, belong in an enclosed space, and even they need the fresh-air ventilation their manual specifies and a working carbon monoxide alarm. Mr. Heater also warns against using them while sleeping. Grills, griddles, camp stoves, fire pits and patio heaters are outdoor-only; using them in a tent, garage, camper or house can kill through carbon monoxide poisoning. Store and change cylinders outdoors, and keep them upright.
Frequently asked questions
How long will a 20 lb propane tank last on a Buddy heater?
About 48 hours on the 9,000 Btu high setting and about 108 hours on the 4,000 Btu low setting, with a full 20 lb (4.7 gallon) tank. You need the hose and fuel filter Mr. Heater specifies to connect a 20 lb tank.
How long does a 1 lb propane cylinder last in a Mr. Heater Buddy?
By the math, about 2.5 hours on high (9,000 Btu) and 5.5 hours on low (4,000 Btu) for a 16.4 oz cylinder. Mr. Heater advertises up to 3 and 6 hours. Expect less in very cold weather, when small cylinders struggle to vaporize fast enough.
How long will a 20 lb tank last on a Blackstone griddle?
With every burner on high, about 7 hours on a 36 inch (60,000 Btu), about 13 hours on a 28 inch (34,000 Btu) and about 18 hours on a 22 inch (24,000 Btu). Most cooks run burners at medium after preheating, so a 36 inch typically gets roughly 12 to 15 hours of real cooking from a 20 lb tank.
How long does a 20 lb propane tank last on a patio heater?
About 9 to 10 hours at the full 46,000 Btu of a typical tall mushroom-style heater, and longer if you turn it down.
How long will a 20 lb tank run an RV furnace?
A 30,000 Btu furnace burning nonstop would empty a 20 lb tank in about 14 hours. Furnaces cycle on and off, so at a 50% duty cycle that stretches to about 29 hours. On a freezing night a furnace can run most of the time.
Sources
- Mr. Heater, MH9BX Portable Buddy (4,000/9,000 Btu; 0.044 and 0.099 gal/hr; 3 and 6 hour claims), MH4B Little Buddy (3,800 Btu), MH18B Big Buddy (4,000/9,000/18,000 Btu).
- Blackstone, 36" griddle (four 15,000 Btu burners), griddle lineup (28" 34,000 Btu; 22" 24,000 Btu).
- Weber, Genesis E-325s (39,000 Btu main burners plus 13,000 Btu sear zone); Spirit II E-310 listing (30,000 Btu); Q 1200 spec sheet (8,500 Btu).
- Coleman, Classic propane stove (2 × 10,000 Btu).
- Amazon Basics, 46,000 Btu patio heater; Outland Living, Firebowl 883 (58,000 Btu).
- Suburban, SF-series furnace service manual (SF-30, 30,000 Btu input).
- EIA, Energy units (91,452 Btu/gal); PERC Technical Pocket Guide (4.24 lb/gal).
- U.S. CPSC, Carbon Monoxide Information Center.
Last reviewed October 25, 2026. Estimates only; see the disclaimer.