What size is my buried oil tank?
You cannot measure a tank you cannot see, but the delivery truck's meter can measure it for you. Stick the tank before the delivery, keep the ticket, and stick it again after. Every tank size predicts a different number of gallons between those two readings, so three numbers identify the tank.
Each line shows what that tank size predicts for the gallons between your two readings, and how far the prediction lands from the ticket.
Enter all three numbers. Bigger deliveries separate the sizes better; 100 gallons or more gives a clean answer.
How it works
The candidates are the standard buried tanks: the 48 inch steel cylinders (550, 1000, and the less common 500) and the fiberglass balls (285, 550, 1000). For each one, the same geometry behind our charts computes the gallons that fit between your before and after readings. The tank whose prediction matches the delivery meter is your tank: a 550 cylinder fits about 417 gallons between 10 and 40 inches, while a 1000 fits about 753 in the same span. The meter does not lie.
- Use the same stick, the same way, both times. Read to the half inch and count only the wet line.
- Take the after reading within a day of the delivery so the burner does not blur the math.
- The whistle stopping the fill early does not matter. The math uses your actual readings, not an assumed full tank.
Common questions
Does this work for above ground tanks too?
The math works on any tank, but an above ground tank is faster to identify with a tape measure: the identification guide has the standard dimensions. This tool earns its keep when the tank is under the lawn.
Nothing matches within a few percent. Why?
The usual suspects are a tilted tank, a fill pipe that enters off center, readings taken with different sticks, or a nonstandard tank. Re-run it on the next delivery with careful readings; if it still will not settle, your installation records or a dealer gauge reading are the next step.
Can I use the gauge instead of a stick?
No. Float and remote gauges read too coarsely for this; the whole method depends on inch-accurate before and after readings. The stick procedure for buried tanks is in how to stick an oil tank.
Why does the size matter once the tank is full?
Every future reading depends on it: 30 inches is 371 gallons on a 550 but 670 on a 1000. Order timing, run-out math, and the oil credit at a closing all start from knowing which chart is yours.