500 gallon propane tank chart
The gauge on a 500 gallon tank shows percent of 500 gal, the tank's water capacity. So every 1% is 5 gal, and 50% means 250 gal. Some answers online say 200 gal for half full, which mixes up the 400 gal you can fill with the 500 gal the percent is measured against. The tank is filled to about 80%, which is 400 gal. That 80% is what people mean by a full 500 gallon tank.
Gauge percent to gallons
The last column is how much a delivery to the 80% line would bring at that reading.
| Gauge | Gallons | To 80% line |
|---|---|---|
| 0% | 0 | 400 |
| 5% | 25 | 375 |
| 10% | 50 | 350 |
| 15% | 75 | 325 |
| 20% | 100 | 300 |
| 25% | 125 | 275 |
| 30% | 150 | 250 |
| 35% | 175 | 225 |
| 40% | 200 | 200 |
| 45% | 225 | 175 |
| 50% | 250 | 150 |
| 55% | 275 | 125 |
| 60% | 300 | 100 |
| 65% | 325 | 75 |
| 70% | 350 | 50 |
| 75% | 375 | 25 |
| 80% (fill line) | 400 | 0 |
| 85% | 425 | 0 |
| 90% | 450 | 0 |
| 95% | 475 | 0 |
| 100% | 500 | 0 |
These match Dead River's gauge table (100 gal at 20%, 250 at 50%, 400 at 80%).
How long will a 500 gallon propane tank last?
It depends on how many gallons your house uses a day, which changes with the weather, the size of the house and what runs on propane (furnace, water heater, stove, dryer). Your own readings give the real rate. Before you have them, how much propane a furnace uses per day estimates it from the furnace rating and the outdoor temperature. Once you have a rate, the table below gives the days until the gauge reaches 20%, the level I use as "empty" in the calculator.
| Gauge now | 1 gal/day | 2 gal/day | 3 gal/day | 4 gal/day | 5 gal/day | 6 gal/day |
|---|---|---|---|---|---|---|
| 80% (300 gal to use) | 300 days | 150 days | 100 days | 75 days | 60 days | 50 days |
| 60% (200 gal to use) | 200 days | 100 days | 66 days | 50 days | 40 days | 33 days |
| 40% (100 gal to use) | 100 days | 50 days | 33 days | 25 days | 20 days | 16 days |
| 30% (50 gal to use) | 50 days | 25 days | 16 days | 12 days | 10 days | 8 days |
A worked example
On 2026-12-01 the gauge reads 70%, which is 350 gal. On 2026-12-15 it reads 55%, 275 gal. No delivery came in between.
- Used: 350 − 275 = 75 gal in 14 days, so 5.36 gal a day.
- Above the 20% line (100 gal): 175 gal.
- Days left: 175 ÷ 5.36 = 32, so the gauge reaches 20% around 2027-01-16.
- At $3.46 a gallon (Maine's statewide average on October 5, 2026) those 14 days cost 259.50, and a fill back to 80% is 125 gal, 432.50.
Open this example in the calculator and change the numbers to yours. It keeps up to six readings and three deliveries in a link you can bookmark.
The 20% line is my suggestion, and the date is an estimate. Follow your supplier's guidance on when to order: Eastern Propane asks for a call at 30%, MFA Oil below 40%. A week of cold weather can use far more than the average.
Other tank sizes
For all sizes side by side see the propane tank percentage chart. What a refill costs at today's price is on the cost to fill a tank page. The math is the same for every home tank: gallons = water capacity × gauge percent ÷ 100. The propane calculator has 120, 250, 325, 500 and 1,000 gal tanks, plus any size you type. Heating with oil instead? See how long heating oil lasts.