Propane tank sizes and days-left calculator
The short answer
Propane tank sizes are given in gallons, but tanks are filled only to 80%. A 500-gallon tank holds about 400 gallons of propane and a 1,000-gallon tank about 800.
Propane days-left calculator
Use this propane usage calculator to see how much propane is in your tank and how many days it will last.
Your numbers
Your answer
About 300 gallons
Your 500-gallon tank at 60% holds about 300 gallons of propane.
- In the tank now300 gallons
- Until 20%about 38 days (5 weeks)
At about 5.2 gallons a day, it will reach 20% in about 38 days (5 weeks).
At a glance
- A full tank reads
- 80%
- 500-gallon tank, full
- About 400 gallons
- One gallon of propane
- 91,452 Btu
- Coldest months here
- December and JanuaryNOAA heating degree days
Propane tank size chart
Propane tanks are named by their size in gallons, but they are filled only to 80%. The extra space leaves room for the gas to expand. So a 500-gallon tank holds about 400 gallons of propane when full.
| Tank size | Full (80%) | Half full (40%) | At 20% |
|---|---|---|---|
| 58 gallons | 46 gallons | 23 gallons | 12 gallons |
| 120 gallons | 96 gallons | 48 gallons | 24 gallons |
| 250 gallons | 200 gallons | 100 gallons | 50 gallons |
| 325 gallons | 260 gallons | 130 gallons | 65 gallons |
| 500 gallons | 400 gallons | 200 gallons | 100 gallons |
| 1,000 gallons | 800 gallons | 400 gallons | 200 gallons |
How the propane usage calculator works
- Gallons in the tank now: tank size x gauge reading / 100.
- Gallons you can use before a refill: tank size x (gauge now - refill mark) / 100.
- Gallons a day, one of three ways. From a heater: its BTU per hour x the hours it runs / 91,452. From your last fill: the gallons delivered / the days since the fill before it. Or a number you already know.
- Days left: gallons you can use / gallons a day.
What it assumes
- You use propane at the same rate every day. In a cold snap you use more, and in a mild spell less.
- A heater's rating is what it burns while it runs. The hours it runs a day are your own estimate.
- The refill mark is your choice. The calculator starts at 20%.
How long does a 500 gallon propane tank last?
It depends on how much you burn. A full 500-gallon tank holds about 400 gallons. At 5 gallons a day, that is about 80 days from full to empty. At 10 gallons a day, about 40 days.
Use goes up in the coldest months. NOAA's climate normals for Bonners Ferry put December and January at the top for heating degree days. That is a measure of how much heating a month calls for.
A Bonners Ferry example
Say your house outside Bonners Ferry has a 500-gallon tank reading 60%. Your furnace label says 80,000 BTU per hour, it runs about 6 hours a day, and you order a refill at 20%.
- In the tank now: 500 x 60 / 100 = 300 gallons.
- To use before a refill: 500 x (60 - 20) / 100 = 200 gallons.
- Gallons a day: 80,000 x 6 / 91,452 = about 5.25 gallons.
- Days left: 200 / 5.25 = about 38 days.
Facts this tool uses
| Fact | Figure | Source |
|---|---|---|
| A full propane tank | Reads 80% on the gauge, to leave room for the gas to expand | Dead River Company, How much fuel is in my tank?80% line checked Oct 28, 2026 |
| Gallons in the tank | Tank size x gauge percent (a 500-gallon tank at 80% holds 400 gallons) | Dead River Company, How much fuel is in my tank?Gauge table checked Oct 28, 2026 |
| Heat in a gallon of propane | 91,452 Btu | U.S. Energy Information Administration, British thermal unitsSample conversion table checked Oct 28, 2026 |
| Bonners Ferry heating degree days | December 1,133 and January 1,125, the two coldest months (base 65°F) | NOAA NCEI, U.S. Climate Normals 1991-2020, Bonners Ferry station (monthly)Monthly heating degree day normals checked Oct 28, 2026 |
Next step
Time to set up a delivery? Propane companies in Bonners Ferry