How long will 100 gallons of heating oil last?
Divide 100 by the gallons your house burns a day. At 2 gallons a day, a mild-weather figure, that is 50 days. At 5 it is 20, and in a cold snap at 8 or 10 it is 10 to 12. The tables below do the division, and a second table starts from the burner's nozzle if you don't know your daily use.
Want your own number? Enter two dated dips in the calculator and it gives gallons a day and days left.
Days by daily use
| Gallons a day | Days | Weeks |
|---|---|---|
| 2 | 50 | 7.1 |
| 3 | 33 | 4.8 |
| 4 | 25 | 3.6 |
| 5 | 20 | 2.9 |
| 6 | 16 | 2.4 |
| 8 | 12 | 1.8 |
| 10 | 10 | 1.4 |
Days are rounded down. Which row is yours depends on the weather and the house: the heating oil use per day page shows how one house moves between the rows as the outdoor temperature drops.
Days from the burner nozzle
The nozzle in the burner is stamped with its gallons per hour. InspectApedia's method multiplies that by the minutes the burner fires each hour, which you watch for yourself, and by 24 hours (InspectApedia). That page calls the nozzle rate conceptual and says it will not tell you how many days of heat you have, because firing time moves with the thermostat, the weather, the building's heat loss and the burner tuning. Treat the table as a range. The 0.65 and 0.85 nozzles are my picks for smaller burners.
| Nozzle gal/hr | 10 min/hr | 15 min/hr | 20 min/hr | 30 min/hr |
|---|---|---|---|---|
| 0.65 | 2.6 gal/day 38 days | 3.9 gal/day 25 days | 5.2 gal/day 19 days | 7.8 gal/day 12 days |
| 0.85 | 3.4 gal/day 29 days | 5.1 gal/day 19 days | 6.8 gal/day 14 days | 10.2 gal/day 9 days |
| 1.00 | 4.0 gal/day 25 days | 6.0 gal/day 16 days | 8.0 gal/day 12 days | 12.0 gal/day 8 days |
Worked example: a 1.0 gallon an hour nozzle that fires 15 minutes of every hour. That is 1.0 × 15 ÷ 60 × 24 = 6 gallons a day, so 100 gallons lasts 16 days.
Where 100 gallons sits on the stick
If the tank is nearly empty, the stick tells you whether you have 100 gallons. The nearest half inch to 100 gallons, from the tank shapes on the chart pages:
| Tank | Stick | Gallons |
|---|---|---|
| 275 gallon, standing up | 17.0 in | 98.9 |
| 275 gallon, lying down | 10.5 in | 99.9 |
| 330 gallon, standing up | 15.0 in | 101.9 |
| 330 gallon, lying down | 9.0 in | 99.8 |
The same 100 gallons is a very different reading lying down than standing up, which is why the chart for your tank matters: 275 gallon or 330 gallon.
A worked example from two readings
A 275 gallon tank standing up, with example dates. On 2026-12-01 the stick reads 23.0 in, 141.0 gal. On 2026-12-15 it reads 17.0 in, 98.9 gal. That is 42.1 gallons in 14 days, 3.01 a day. The 99 gallons left, less a 10% reserve (26.8 gal), last 23 more days, to around 2027-01-07. At $5.97 a gallon (Maine's statewide average on October 5, 2026) the two weeks cost $251.21.
Open this example in the calculator and swap in your own dips.
Leave a margin
The days above are days to empty. Delivery can take a few days, so order while some oil is left. The calculator counts a reserve you set, 10% by default, as empty.
Related
- How long will heating oil last? The same math for any amount, with the formula spelled out.
- Gallons in a quarter tank of oil: gauge marks for 275, 330 and 550 tanks.
- What a fill costs at current Maine prices.