Feature

A 20-lb propane tank running a 3-burner gas grill lasts about 11.4 hours.

Compare 9 propane tank sizes against 11 household appliances by BTU draw, then use the calculator to estimate runtime hours for any tank-appliance pairing.

By Nora Callahan · August 2, 2026 · 1 min read

Runtime is arithmetic: a tank’s total usable BTU divided by an appliance’s BTU-per-hour draw. A 20-lb cylinder holds about 431,400 BTU, enough to run a 3-burner gas grill’s main burners (38,000 BTU/hr) for roughly 11.4 hours. Swap in a furnace, generator, or space heater and the number changes with the draw, not the tank. The table below covers 9 tank sizes and 11 appliances — all 20 rows, sourced and sortable.

Sort and filter. Click any column header to sort by weight, gallons, BTU, or draw, or pick a tank and appliance in the calculator to get your own runtime estimate.

The Data

All 20 rows. Tank rows carry propane weight, usable gallons, and total BTU. Appliance rows carry BTU-per-hour draw. Click any column header to sort; a dash means that column doesn't apply to that row type.

Table	Item	Propane Weight (lb)	Usable Gallons	Total BTU	BTU/hr Draw	Notes
tank	1 lb disposable cylinder	1	0.24	21,569	—	Camping-canister size; propane weight = full-cylinder net weight
tank	20 lb / BBQ cylinder	20	4.72	431,400	—	Standard grill-exchange cylinder; 20 lb rating already reflects the properly-filled amount
tank	30 lb cylinder	30	7.08	647,100	—	Common for larger grills/RVs
tank	40 lb cylinder	40	9.43	862,800	—	Common for RVs, food trucks, livestock heaters
tank	100 lb cylinder	100	23.58	2,156,900	—	Common for fireplaces, dryers, small standby loads
tank	120 gal stationary tank	407	96	8,779,400	—	120 gal is the tank's water capacity; legally filled to 80% = 96 usable gal
tank	250 gal stationary tank	848	200	18,290,400	—	250 gal water capacity; 80% fill = 200 usable gal
tank	500 gal stationary tank	1,696	400	36,580,800	—	500 gal water capacity; 80% fill = 400 usable gal
tank	1000 gal stationary tank	3,392	800	73,161,600	—	1000 gal water capacity; 80% fill = 800 usable gal
appliance	Gas grill (3-burner, main burners)	—	—	—	38,000	Weber Genesis E-330, main burners only (excludes side burner/sear station)
appliance	Patio heater (standing, propane)	—	—	—	48,000	AZ Patio Heaters 87" tall standing model, high setting
appliance	Portable generator, ~2.7 kW class	—	—	—	17,255	Champion 4000W dual-fuel inverter; computed from mfr's stated 20 lb tank / 25 hr at 1/4 load
appliance	Portable generator, ~6.75 kW class	—	—	—	78,432	Champion 7500W dual-fuel; computed from mfr's stated 20 lb tank / 5.5 hr at 1/2 load
appliance	Whole-home standby generator, 22 kW	—	—	—	355,000	Generac Guardian 22kW at full/rated load; mfr spec sheet states 142 ft3/hr LP x 2,500 BTU/ft3
appliance	Furnace (single-stage, 80% AFUE)	—	—	—	80,000	Goodman GR9S800804BN input rating
appliance	Tankless water heater	—	—	—	199,000	Rinnai RXP199iN, maximum input
appliance	Tank water heater (40 gal)	—	—	—	40,000	Rheem PRO+G40-40N-RH62 atmospheric, low-NOx burner
appliance	Range (6-burner cooktop + oven)	—	—	—	90,500	Thor Kitchen ARG36LP, all 6 burners (72,000) + oven bake burner (18,500) running at once (worst case)
appliance	Fireplace (ventless propane insert)	—	—	—	32,000	Duluth Forge FDF400RT-ZC dual-fuel insert
appliance	Space heater (portable radiant)	—	—	—	18,000	Mr. Heater Big Buddy, maximum setting

Estimate Your Runtime

Tank size

Appliance

11.4hours

≈ 0.5 days of continuous use — 20 lb / BBQ cylinder (431,400 BTU) ÷ Gas grill (3-burner, main burners) (38,000 BTU/hr)

Sources

1. Units and calculators explained (propane heat content: 1 gallon = 91,452 Btu)
U.S. Energy Information Administration · primary
EIA's standard Btu conversion factor table; used as the propane BTU/gallon constant
2. Alternative Fuels Data Center: Fuel Properties Comparison (propane LHV 84,250 Btu/gal, HHV 91,420 Btu/gal)
U.S. Department of Energy · primary
Corroborates EIA's Btu/gal figure within ~0.03%
3. Propane (liquid) Weight per Gallon (4.24 lb/gal)
TankVolumeCalc.com · secondary
States density is 'Saturated liquid at 60°F per GPA/NFPA 58'; used as the propane lb/gallon constant
4. The 80% Rule: More Than Just Allowing Room for Expansion
Propane Insider · secondary
Explains the 80% fill rule as vapor space for thermal expansion
5. Propane Tank Levels: The 80% Rule
Wilcox Energy · secondary
Explicitly cites NFPA 58 (Liquefied Petroleum Gas Code) as the regulatory basis for the 80% fill rule
6. Propane
Wikipedia · secondary
Corroborates density (~4.2 lb/gal @ 60°F), 1.5%/10°F thermal expansion, and the 400/500-gallon 80%-fill example
7. Propane Tank Sizes — Dimensions, Capacity & Gallons
TankVolume.com · secondary
Cross-check: cylinder gallons-per-lb and stationary-tank 80%-fill lb figures matched independently computed values
8. Propane Tank Capacity Guide (All Sizes) Gallons, Weight
GudGear · secondary
Cross-check: cylinder full-weight/empty-weight table confirms nominal lb rating = net propane weight
9. Weber Genesis E-330 owner's manual
ManualsLib (Weber manual mirror) · secondary
Main burners: 38,000 BTU-per-hour input
10. Patio Heaters
AZ Patio Heaters · secondary
Manufacturer's own site; 87" tall standing propane heater listed at 48,000 BTU's
11. 4000W Dual Fuel Inverter, Model 201050
Champion Power Equipment · primary
Spec table: 'Propane Run Time at 1/4 Load: 25 h.' on a 20 lb tank, 2,700W propane running watts
12. 7500W Electric Start Dual Fuel Generator, Model 201281
Champion Power Equipment · primary
Spec table: 'Propane Run Time at 1/2 Load: 5.5 h.' on a 20 lb tank, 6,750W propane running watts
13. 16/20/22kW Guardian Series Standby Generator Spec Sheet
Generac · primary
Fetched via r.jina.ai reader proxy (direct fetch returned unreadable binary). Full-load LP consumption: 142 ft3/hr (3.90 gal/hr); sheet instructs multiplying ft3/hr x 2,500 for LP to get BTU/hr
14. Goodman GR9S800804BN 80% AFUE Gas Furnace listing
SupplyHouse.com · secondary
Fetched via r.jina.ai reader proxy (direct fetch 403'd). Spec table: 'BTU Input: 80000'
15. RXP199iN condensing tankless water heater
Rinnai America · primary
Product spec: '199000 BTU (maximum)'
16. Rheem PRO+G40-40N-RH62 40-gal gas water heater listing
US Supply · secondary
'40,000 BTU/hr low-NOx burner' per Rheem spec, 40.4 GPH recovery at 90°F rise
17. 36-Inch Contemporary Professional LP Range, ARG36LP
Thor Kitchen · primary
Fetched via r.jina.ai reader proxy (direct fetch rate-limited). Per-burner BTU: 12,000/18,000/12,000/9,000/12,000/9,000; oven bake 18,500 BTU, broil 13,500 BTU
18. Duluth Forge Dual Fuel Ventless Gas Fireplace Insert - 32,000 BTU, FDF400RT-ZC
Amazon (product listing) · secondary
Title/meta: '32,000 BTU'; matches Home Depot and Lowe's listings for the same model number
19. Mr. Heater Big Buddy propane heater listing
Ace Hardware · secondary
'18000 Btu/h' maximum setting

Method

Constants (BTU/gal, lb/gal, 80% fill rule) sourced first from EIA, DOE AFDC, and NFPA-58-citing secondary sources, then cross-checked against two independent propane-tank-size charts (tankvolume.com, gudgear.com) whose lb figures for 120/250/500/1000 gal tanks matched this page's computed values almost exactly. WebSearch's session budget was exhausted after 2 queries, so all subsequent searches used the DuckDuckGo HTML endpoint (https://html.duckduckgo.com/html/?q=...) via WebFetch, ~25 distinct queries total. Three URLs (Generac's spec-sheet PDF, SupplyHouse's Goodman listing, Thor Kitchen's product page) were fetched through the r.jina.ai reader proxy after the direct WebFetch failed (unreadable binary PDF, 403, and 429 respectively) or timed out. Arithmetic: BTU/lb = 91,452 BTU/gal ÷ 4.24 lb/gal = 21,568.87 (computed, not a directly-published figure). Cylinder tanks (1-100 lb): usable_gallons = nominal_lb ÷ 4.24, since the nominal cylinder weight already represents the properly-filled (80%-rule-compliant) amount by industry convention. Stationary tanks (120-1000 gal): the nominal number is the tank's water capacity; usable_gallons = nominal_gal x 0.80 per the 80% rule, propane_weight_lb = usable_gallons x 4.24, total_btu = usable_gallons x 91,452. Portable generator BTU/hr draw was computed from each manufacturer's own stated propane runtime on a 20 lb tank (lb x 21,568.87 BTU/lb ÷ hours), not published directly by the manufacturer as a BTU/hr figure. All other appliance BTU/hr figures are manufacturer-stated input ratings, fetched directly from the spec/product page. The Home Depot listing for a Hampton Bay 48,000 BTU patio heater could not be verified (403 on direct fetch and via r.jina.ai) and was replaced with a directly-verified 48,000 BTU model from AZ Patio Heaters' own site.

Gaps: RV/camper propane refrigerator BTU/hr draw: we couldn't find one. Multiple targeted searches and direct fetch attempts against Dometic's own installation manual, RV parts retailers (RV Parts Country, Camping World), and Norcold spec pages turned up capacity/voltage/amperage data but no manufacturer-published BTU/hr gas-consumption figure; the only concrete numbers found were anecdotal owner-forum reports of gallons-per-day usage, which we did not treat as sourced. This row was dropped rather than estimated.