Find out how long your propane tank will last, your daily burn rate, and when to schedule your next refill.
Enter BTU rating and daily hours for each appliance you use. Leave hours at 0 to exclude an appliance.
| Appliance | BTU/hr Input | Hours / Day | Gal / Day |
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Every propane appliance has a BTU (British Thermal Unit) input rating — the amount of energy it consumes per hour when running at full capacity. One gallon of liquid propane contains approximately 91,500 BTU of energy. To find how many gallons an appliance uses, divide its BTU/hr rating by 91,500, then multiply by the number of hours per day it runs:
Gallons per day = (BTU/hr × Hours/day) ÷ 91,500
For example, an 80,000 BTU furnace running 6 hours per day uses (80,000 × 6) ÷ 91,500 = 5.25 gallons per day. Add up every appliance to get your total daily consumption, then divide your available propane by that number to find how many days until your tank runs out.
The size printed on your tank is its total physical capacity, but you never fill it completely or run it completely empty. Propane tanks are filled to a maximum of 80% capacity — this "outage space" is required because liquid propane expands with temperature, and a fully packed tank would have no room for thermal expansion, creating dangerous pressure. A 500-gallon tank is therefore filled to a maximum of 400 gallons.
On the empty end, you should never let your tank drop below 5% — at very low levels, the vapor pressure can fall too low for proper appliance operation, and residual moisture and odorant sediment can contaminate regulators. In practice, most propane suppliers and experienced users treat 20% as the practical empty point — it is the universally recommended call-for-refill threshold. Running to 5% or less risks running out unexpectedly and requires a technician to check your system and relight pilots before refilling.
If you don't know your appliance's BTU rating, check the manufacturer's data plate (usually on the back or side of the unit) or look up the model online. Here are typical ranges to help you estimate:
Note that appliances rarely run at full BTU input continuously. A furnace cycles on and off based on thermostat demand. A range burner runs at partial capacity most of the time. The "hours per day" figure in this calculator represents equivalent full-load hours — if your furnace runs at full blast for 3 hours and cycles for 6 hours total, entering 3–4 hours is reasonable.
For most propane users, heating is the dominant cost, and consumption in January can be 5–10 times higher than in July. A home that uses 3 gallons per day in winter may use only 0.3–0.5 gallons per day in summer for water heating, cooking, and a dryer. This calculator gives you a snapshot based on your current appliance settings — for annual planning, you may want to calculate separately for your winter and summer usage profiles and average them together by season length.
A useful rule of thumb: whole-home propane heating in a well-insulated 2,000 sq ft house in a cold climate (Zone 5–6) typically uses 800–1,200 gallons per heating season. Milder climates (Zone 3–4) or better insulation can halve that figure. Adding a wood stove or pellet stove as a supplemental heat source for the coldest months is one of the most effective strategies for cutting propane bills.
Propane and natural gas deliver the same energy content per cubic foot, but propane is more energy-dense in liquid form and is purchased differently (by the gallon rather than by the therm). At $3.00/gallon, propane costs about $32.79 per million BTU. Natural gas at $1.20/therm costs about $12.00 per million BTU — propane is typically 2–3 times more expensive than natural gas. However, natural gas is only available where pipelines exist. For rural properties off the gas grid, the comparison is against electric resistance heat (usually the most expensive option) or electric heat pumps (most efficient in moderate climates). In cold climates, a high-efficiency propane furnace often beats an air-source heat pump below 20°F. Keep an eye on propane prices — they are tied to crude oil markets and can swing significantly from season to season.
Running your propane tank below 20% is a risk most experienced propane users take seriously. Beyond the obvious risk of running out in the middle of a cold night, very low tank levels create several technical problems: vapor pressure drops at low fill levels, which can cause burners to starve and pilot lights to extinguish; odorant (ethyl mercaptan, the substance that gives propane its distinctive smell) can settle to the bottom of a nearly empty tank and interfere with regulators; and if you run completely out, air and moisture can enter the lines, requiring a licensed technician to perform a pressure check and relight all appliances before your delivery. Most suppliers offer automatic delivery programs that keep your tank filled before it hits 20% — these programs are worth using if propane is your primary heat source.
It depends entirely on your heat load and climate. A 500-gallon tank filled to 80% holds 400 gallons. If your home uses 5 gallons per day in winter, that's 80 days — about 2.5 months of heating. A more efficient home using 2 gallons per day gets 200 days of supply. Use this calculator with your actual furnace BTU rating and typical daily run hours for a precise answer.
The gauge on top of your tank shows percentage of capacity, not gallons. A 500-gallon tank at 40% contains 200 gallons. Gauges can be inaccurate when temperatures change rapidly — cold weather causes liquid propane to contract, making the gauge read slightly lower than actual. Never trust a gauge reading below 20% as "still have some time" — call for a refill immediately.
An 80,000 BTU furnace uses 80,000 ÷ 91,500 = 0.87 gallons per hour at full fire. A 100,000 BTU furnace uses about 1.09 gallons per hour. Most furnaces do not run continuously — they cycle based on thermostat demand, so actual daily consumption is much lower than the theoretical max.
Yes, in most markets propane prices are 10–30% lower in spring and summer (April–August) than in the fall and winter heating season, when demand spikes. If your tank is large enough to store a full season's supply, buying in summer and topping off before the heating season can meaningfully reduce your annual fuel cost.
If you run your tank completely empty, air can enter the gas lines. Before your supplier can refill your tank and restore service, a licensed technician must inspect all connections, perform a pressure test of the gas lines, relight all pilot lights, and verify safe operation of every appliance. This service call typically costs $50–$150 and causes an inconvenient wait — often the worst time being in the coldest weather. The 20% refill rule exists specifically to prevent this scenario.