How many gallons are in a quarter tank of oil?
On a 275 gallon tank the 1/4 mark means about 69 gallons, 1/2 means about 138 and 3/4 about 206. PickHVAC's measuring chart lists the same three figures for a 275 (PickHVAC). Below are the marks for the other common sizes, and a check on how far a float gauge can be trusted.
Have a stick instead of a dial? Convert inches to gallons for your tank, or open the calculator at a quarter of a standing 275.
Gauge marks to gallons
Each cell is the mark times the label size, so a quarter of a 330 is 330 ÷ 4. The last column is 90% of the label size, the average maximum fill PickHVAC gives (it quotes 220 to 248 gallons for a 275). A delivery rarely tops the tank to the label.
| Tank | 1/8 | 1/4 | 1/2 | 3/4 | Usual max fill |
|---|---|---|---|---|---|
| 275 gal | 34.4 | 68.8 | 137.5 | 206.3 | 248 |
| 330 gal | 41.3 | 82.5 | 165.0 | 247.5 | 297 |
| 550 gal | 68.8 | 137.5 | 275.0 | 412.5 | 495 |
When the gauge and the stick disagree
The table above treats a quarter as a quarter of the volume. A float gauge moves with the oil level, and on a rounded tank level and volume are not the same thing. If a dial follows height, a quarter of the way up holds this much, using the tank shapes on the 275 gallon chart:
| 275 gallon tank | 1/4 of the height | 1/2 of the height | 3/4 of the height |
|---|---|---|---|
| Standing up | 56.9 gal (11.00 in) | 134.0 gal (22.00 in) | 211.0 gal (33.00 in) |
| Lying down | 58.9 gal (6.75 in) | 134.0 gal (13.50 in) | 209.1 gal (20.25 in) |
A quarter of the height holds a little less than a quarter of the oil (about 57 to 59 gallons against 69), and three quarters of the height holds a little more (about 210 against 206). Those differences come from my 267.9 gallon geometric model of the tank, so a real tank shifts them slightly. I can't tell which way your gauge reads, so dip the tank once when the dial sits on a mark and compare. PickHVAC also notes that older gauges that don't account for temperature can show a winter tank fuller than it is.
A worked example: when to call
The dial on a 275 gallon tank sits on 1/4, so about 68.8 gallons. Counting the last 10% (27.5 gallons) as empty leaves 41.3 usable. At 4 gallons a day that is 41.3 ÷ 4, so 10 days. A supplier needs a few days to deliver, so this is the time to call. At 2 gallons a day in mild weather the same quarter lasts about twice as long.
Your own rate beats a guess: two dated readings give days left, and the 100 gallon page does the same math for a smaller amount.
Related
- 330 gallon oil tank chart: the marks as stick inches for both ways up.
- 550 gallon oil tank chart: a round tank on its side.
- Cost to fill an oil or propane tank: gallons to max fill times the price.