Heating Oil Tank Chart — Inches to Gallons

Calculated heating-oil tank estimates based on standard nominal residential tank dimensions. Actual tanks vary by manufacturer, installation, tilt, dents, fittings, unusable bottom volume, and fill-room practices.

How to read your tank with a stick

The most reliable way to check a heating oil tank is to measure the oil depth directly. Remove the cap or plug on top of the tank, lower a long, clean stick straight down until it touches the bottom, withdraw it, and read how many inches of the stick are wet with oil. Then find that depth in the chart below under your tank size. Make sure the stick is long enough that it cannot fall into the tank.

Float gauges built into the tank give only a rough indication and can stick or fail due to sludge, so a stick reading is more dependable. The number you get is an approximate estimate, not an exact measurement.

Tank dimensions used for these estimates

Oil depth to gallons chart (calculated estimates)

Find the oil depth in inches in the left column, then read across to your tank size. Values are approximate calculated estimates. Blank cells mean that depth is above the top of that tank.

Why your tank is never filled to the top

Oil companies leave room for thermal expansion and do not fill a tank to its rated capacity. A 275-gallon tank is typically filled to around 250 gallons (roughly 6 inches below the top), a 330 to around 300, a 500 to about 450, a 550 to about 500, and a 1000 to about 900. So a "full" delivery is normal even though the gauge does not read at the very top.

Oil below the tank's take-up screen near the bottom is generally not usable by the burner, so the last inch or two of indicated oil should not be counted on when planning your next delivery.

Assumptions and limitations

These figures are approximate calculated estimates based on ideal tank geometry for each nominal size, not official tank-gauge readings. The horizontal 275 and 330-gallon tanks are modelled with an obround (stadium) cross-section, the larger 500, 550 and 1000-gallon tanks as horizontal cylinders, and the upright 275 and 330-gallon tanks with a vertical linear model. Actual capacity varies with manufacturer, exact dimensions, tank tilt, dents or deformation, fittings, and sediment or water at the bottom of the tank. Use these numbers for planning and ordering, not for billing or custody-transfer measurement. If your tank's dimensions differ from those listed above, the readings will not match.

Disclaimer: This chart provides approximate calculated estimates only. Confirm your tank's exact size and configuration before ordering, and rely on your oil supplier's measurement for delivery and billing.

References and cross-checks

Standard residential heating-oil tank dimension references and manufacturer-style tank charts were used to cross-check common 275, 330, 500, 550 and 1000-gallon tank sizes. Commercial oil-provider charts were used only as non-linked cross-checks. Actual usable gallons can differ by manufacturer, tank tilt, fittings, sludge or water at the bottom, and delivery fill-room practice.

Volume conversions follow standard U.S. customary definitions (1 US gallon = 231 cubic inches), as documented on our methodology page.

Have a tank that isn't a standard heating-oil size? Use the tank volume calculator to compute volume and partial fill for any cylinder, rectangle, oval or capsule shape.