Most oil tank gauges display the amount of remaining fuel in terms of fractions, with most displays using 1/8 or 1/4 increments, and the displayed fraction is a percentage of the 275 gallons. While most oil tanks are 275 gallons, a full tank typically only holds 245 to 255 gallons because of air or debris that can accumulate in the tank's bottom.
Heating oil tank gauges vary in accuracy, so it is advisable to fill the tank once it reaches about 1/4 full to ensure the tank does not completely run out of oil, which requires additional labor and steps for the system to operate properly again. The fractions listed on the gauge mean a 275-gallon tank has approximately the following amount remaining:
- 1/8 of a tank is about 32 gallons
- 1/4 of a tank is about 65 gallons
- 3/8 of a tank is about 95 gallons
- 1/2 of a tank is about 130 gallons
- 5/8 of a tank is about 160 gallons
- 3/4 of a tank is about 192 gallons
- 7/8 of a tank is about 223 gallons
- A full tank is about 245 to 255 gallons
Because situations and systems vary, different homes will burn through the heating oil at different rates, and the home's size, temperature and furnace efficiency all affect the rate of use.