550 gallon underground oil tank chart
If your home has a buried oil tank, odds are it is a 550: the most common underground residential size, a 48 inch round cylinder about six feet long. You read it through the fill pipe at grade. Drop a long clean stick to the tank bottom, pull it, read the wet line in inches, and convert below.
gallons % of a full 550 gallon underground tank
Enter a reading to convert it, fill the tank pictures, and highlight your row in the chart below.
| Inches | Gallons | Inches | Gallons |
|---|---|---|---|
| 1″ | 3 | 25″ | 297 |
| 2″ | 8 | 26″ | 312 |
| 3″ | 15 | 27″ | 327 |
| 4″ | 22 | 28″ | 342 |
| 5″ | 31 | 29″ | 356 |
| 6″ | 41 | 30″ | 371 |
| 7″ | 51 | 31″ | 385 |
| 8″ | 62 | 32″ | 399 |
| 9″ | 73 | 33″ | 413 |
| 10″ | 85 | 34″ | 427 |
| 11″ | 97 | 35″ | 441 |
| 12″ | 110 | 36″ | 454 |
| 13″ | 123 | 37″ | 467 |
| 14″ | 137 | 38″ | 479 |
| 15″ | 151 | 39″ | 491 |
| 16″ | 165 | 40″ | 502 |
| 17″ | 179 | 41″ | 513 |
| 18″ | 193 | 42″ | 523 |
| 19″ | 208 | 43″ | 533 |
| 20″ | 222 | 44″ | 542 |
| 21″ | 237 | 45″ | 549 |
| 22″ | 252 | 46″ | 556 |
| 23″ | 267 | 47″ | 561 |
| 24″ | 282 | 48″ | 564 |
Generated 2026-06-12. Computed from nominal tank geometry at 231 cubic inches per gallon. Actual tanks vary by manufacturer; cross-check your tank data plate.
Reading the numbers
- Full computes to about 564 gallons, a bit over the 550 nameplate. Cylinder geometry runs generous; the nominal name rounds down.
- Half is 24 inches, 282 gallons. A quarter (about 141 gallons) reads near 14.5 inches. In January, that quarter mark is the reorder line worth respecting.
- The middle band moves about 15 gallons per inch. Near the very top and bottom of the circle each inch holds much less, which is why the chart flattens at both ends.
- Same 48 inch scale as the 500 and the 1000. A 30 inch wet line means 371 gallons here, 335 on a 500, and 670 on a 1000. Identify the tank before you trust any number.
- Buried-tank technique matters: longer stick, wet line only, cap back on firmly. The procedure, including the water-finding paste check, is in how to stick an oil tank.
Common questions
How do I know my buried tank is a 550?
The 550 is the most common buried residential size, but common is not certain. Installation records, the original permit, or your oil company's account notes usually name it. What size is my oil tank walks through the clues.
Why does full read 564 when the tank is called a 550?
About 564 gallons is the computed capacity of the nominal 48 by 72 inch cylinder; the 550 label rounds it down. Your records or the installer's paperwork stay the authority on what was actually buried.
Could it be a 1000 instead of a 550?
Possibly: both are 48 inches deep, so stick depths look identical and only the buried length differs. The same 30 inch reading is 371 gallons on a 550 and 670 on a 1000. If your tank serves a large or two-family property, check the records before assuming.
When should I order oil?
Do not let a buried 550 ride below a quarter, about 141 gallons at 14.5 inches, during the heating season. Deliveries can be days out in a cold stretch. When to order heating oil covers the timing.
Related
- 1000 gallon underground chart (same depth, double the oil)
- 500 gallon underground chart
- How to stick an oil tank (buried-tank procedure)
- When to order heating oil