500 gallon underground oil tank chart
A buried 500 is a round steel cylinder, 48 inches across and about 65 inches long, with nothing showing above grade but the fill and vent pipes. Fair warning from the delivery side: most buried residential tanks are 550s or 1000s, and true 500s are the exception, so confirm the size before trusting this chart. One delivery and two stick readings will identify it: see the buried tank size calculator. To read it, lower a long clean stick through the fill pipe to the tank bottom and count only the wet inches. The dry length above the oil is riser, not tank.
gallons % of a full 500 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″ | 268 |
| 2″ | 7 | 26″ | 282 |
| 3″ | 13 | 27″ | 295 |
| 4″ | 20 | 28″ | 308 |
| 5″ | 28 | 29″ | 322 |
| 6″ | 37 | 30″ | 335 |
| 7″ | 46 | 31″ | 348 |
| 8″ | 56 | 32″ | 361 |
| 9″ | 66 | 33″ | 373 |
| 10″ | 77 | 34″ | 386 |
| 11″ | 88 | 35″ | 398 |
| 12″ | 100 | 36″ | 410 |
| 13″ | 111 | 37″ | 421 |
| 14″ | 124 | 38″ | 432 |
| 15″ | 136 | 39″ | 443 |
| 16″ | 149 | 40″ | 453 |
| 17″ | 161 | 41″ | 463 |
| 18″ | 174 | 42″ | 472 |
| 19″ | 188 | 43″ | 481 |
| 20″ | 201 | 44″ | 489 |
| 21″ | 214 | 45″ | 496 |
| 22″ | 228 | 46″ | 502 |
| 23″ | 241 | 47″ | 507 |
| 24″ | 255 | 48″ | 509 |
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 509 gallons. A cylinder of this size actually works out a touch over its nominal 500 name.
- Half is 24 inches, 255 gallons: the center of the 48 inch circle. A quarter (about 127 gallons) sits near 14.5 inches.
- The middle of the circle moves about 13.5 gallons per inch. The first and last few inches move far less, because the round shell curves away from the stick.
- The buried-tank procedure has its own tricks: a 6 to 8 foot stick, a fill cap that may need persuasion, and reading the wet line only. It is all in how to stick an oil tank.
Common questions
How do I read a tank I cannot see?
Through the fill pipe. Open the fill box at grade, unscrew the cap, and lower a 6 to 8 foot wooden stick straight down until it rests on the tank bottom. Read only the wet line; everything dry above it is the riser. The full procedure is in the buried-tank section of how to stick an oil tank.
Is my buried tank a 500 or a 550?
Both are 48 inches deep, so the stick cannot separate them; the difference is length you cannot see (about 65 inches against 72). Installation records, the original permit, or your oil company usually know. Start with what size is my oil tank.
Why does the chart go past 500 gallons?
The computed capacity of a 48 by 65 inch cylinder is about 509 gallons, and the nominal name rounds it to 500. Actual tanks vary by manufacturer, so treat your records or data plate as the authority on capacity.
How do I check for water in the tank?
Coat the bottom few inches of the stick with water-finding paste before lowering it. The paste turns color on contact with water and shows you the depth sitting under the oil. An inch or more means call your oil company before it reaches your filter.
Related
- 550 gallon underground chart (same diameter, 7 inches longer)
- 1000 gallon underground chart
- How to stick an oil tank (buried-tank procedure)
- What size is my oil tank?