I'm not sure if my tank holds 250, 275, or 300 gallons. Is there a way to determine the size?

The tank is oval shape and 60" X 40" X 27".

  • How about you look up the formula for the volume of a cylinder and look up the number of cubic inches in a gallon and work it out? – Transistor Dec 11 '15 at 1:07
  • @transistor, to be fair, these tanks are not typically round cylinders, they are oblong. (If it was a circular cylinder there would only be two measurements, right?) – batsplatsterson Dec 11 '15 at 7:52
  • I made a mistake and used cylindrical instead of oval in the post. – Jay P. Dec 11 '15 at 12:28
  • Brush off the dirt and read the label on the tank? There usually is one; it will include the UL listing and various other data including size/capacity. – Ecnerwal Dec 11 '15 at 16:57

The most common size is 275 gallons, which measures 44” x 60” x 27”

  • 2
    Since his tank is 40" rather than 44", or 10% less, it is likely that his tank holds about 10% less so 250 gallons seems the correct capacity. – Barry Dec 11 '15 at 0:29
  • Traditionally, not all of the tank capacity is usable anyway -- the tank whistle isn't at the exact top of the tank, and the tap the bottom is a bit above the bottom to avoid sludge and water. – gbronner Dec 11 '15 at 14:25

Your tank is in fact not oval, but stadium in profile. (Yes, that's where the sports facilities got their name.)

In the case of a tank measuring 60" × 40" × 27", your volume is (nominally) that of a box measuring 60 × (40-27) × 27 plus a cylinder of diameter 27 (radius 13.5) and length 60.

60 × 13 × 27 = 21,060 cubic inches (91.17 gallons)

π × 13.52 × 60 = 34,353 cubic inches (148.71 gallons)

Add those together and you get 239.88 gallons. 240 gallons is a reasonably common size for a residential oil tank.


You can also do this by measuring the amount of fuel delivered and the corresponding change in depth of the oil in your tank; this is also a great way to see if your oil dealer is skimming:

  1. Put a dipstick in the oil before your next fill-up to measure the height of oil above the bottom.
  2. Fill the tank. Record the number of gallons delivered.
  3. Then put a dipstick in after the oil is refilled.
  4. look up the two values in this chart, and match the difference by column to the amount of oil that you just had delivered. This will tell you which tank size your tank is closest to.


  • That chart seems to apply to cylindrical tanks. – isherwood Dec 11 '15 at 17:47
  • There are similar charts for oval tanks -- thought that that one applied. – gbronner Dec 11 '15 at 21:51

40 x 27 x 60 inches is 64800 cubic inches total tank volume including the tank walls.

There are 231 cubic inches in a gallon.

64800/231 = 280 gallons

Since these dimensions are OUTSIDE tank dimensions, you need to account for the wall thickness. Looks like 275 gallons based on approximate interior volume and filled to the brim. That's the math of it.

  • 3
    That calculation would be for a rectangular "box" shaped tank, most of these tanks are an oblong shape rather than rectangular. – batsplatsterson Dec 11 '15 at 7:50

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