275 Gallon Oil Tank (Horizontal) dimensions

Nominal rating versus real geometry

A tank's name is a trade label. Its geometry is a measurement. On a aboveground heating-oil tank these two numbers are related but not equal, and knowing which one you are quoting matters whenever the figure ends up on an invoice, a permit or a purchase order.

Rated 275 gal. Computed from the dimensions in the table above: 267.9 gal. The geometry comes out 7.1 gallons short of the label — 2.6 %. Published exterior dimensions and internal volume are not the same thing, and rounded corners, ribs and wall thickness account for most of the gap.

Densities are the reference values tabulated on our methodology page, near 60–70 °F. Real fluids vary with temperature, grade and composition — a 10 °F swing moves a hydrocarbon density by roughly 0.4 %. Add the empty vessel weight to get a gross figure.

Siting, fill and service

Three dimensions decide whether this tank fits a real basement, and only one of them is in the capacity: overall height including legs (it has to clear the ceiling and leave room to lift a stick out of the fill port), footprint, and the diagonal it has to travel through the doorway and down the stairs. Measure the route before the tank arrives, not after.

The fill and vent piping matters as much as the tank. Under NFPA 31 the vent must be sized and routed so the tank cannot pressurise during a delivery, and the whistle must be audible at the fill point — a driver who cannot hear the whistle stop is a driver who will overfill. A tank that has been overfilled once has almost certainly had oil in the vent line.

Leave working room at the gauge end. A tank pushed tight into a corner is a tank nobody sticks, and an unstuck tank is where the surprise runs-out come from.

The standards behind this tank

An aboveground fuel-oil supply tank of this class is built to UL 80 and installed under NFPA 31, which governs where it may sit, how it is vented and filled, and its clearance to the appliance. The fuel itself is specified by ASTM D396 — that specification's density range is why heating-oil weights are quoted as a band rather than a single figure.

If the tank serves a commercial site rather than a house, 40 CFR § 112 may also apply: the SPCC rule brings in facilities whose aggregate aboveground oil storage capacity exceeds 1,320 US gallons where a discharge could reach navigable waters, and requires secondary containment for the entire capacity of the largest single container plus freeboard for precipitation. Two 275s and a 550 clear that threshold.

None of those standards make a gauge chart authoritative. For a measurement that has to survive a dispute, the tank needs a capacity table produced by physical calibration under ISO 7507-1 or the equivalent API chapters.

For depth-by-depth volumes on this tank, use the inch-by-inch chart; for a different set of dimensions, the dip chart generator will build one.

Sources and standards

The geometry on this page is computed, not copied. These are the documents that define the units it is expressed in and the codes that govern a aboveground heating-oil tank in service.

1. NFPA 31 — Standard for the Installation of Oil-Burning EquipmentNational Fire Protection AssociationPaid standard — cited by designation; obtain from the publisher.Governs how fuel-oil supply tanks are installed, vented, filled and located, including tank-to-appliance clearances and fill and vent piping. Adopted, often with amendments, by most US states.
2. UL 80 — Standard for Steel Tanks for Oil-Burner Fuel and Other Combustible Liquids; UL 58 — Steel Underground Tanks for Flammable and Combustible LiquidsUL Standards & EngagementPaid standard — cited by designation; obtain from the publisher.The construction standards behind the familiar 275 and 330 gallon aboveground heating-oil tanks (UL 80) and steel USTs (UL 58). They govern steel gauge, seams, fittings and leak testing — not gauge-chart accuracy, which is why a listed tank still needs its own capacity table for anything measured.
3. ASTM D396 — Standard Specification for Fuel OilsASTM InternationalPaid standard — cited by designation; obtain from the publisher.Defines the grades of fuel oil, including No. 2 heating oil. It sets the density and viscosity ranges this site uses for weight and thermal-expansion figures — which is why a heating-oil weight is a range rather than a single number.
4. 40 CFR § 112.8(c)(2) — Spill Prevention, Control, and Countermeasure Plan requirements for onshore facilitiesU.S. Environmental Protection Agency, via the electronic Code of Federal Regulationshttps://www.ecfr.gov/current/title-40/chapter-I/subchapter-D/part-112/subpart-B/section-112.8Requires secondary containment sized for the entire capacity of the largest single container, plus sufficient freeboard to contain precipitation. Note that the rule itself does not state “110 %” — that is a common design convention layered on top of the regulatory floor.
5. Handbook 44, Appendix C — General Tables of Units of MeasurementNational Institute of Standards and Technology, U.S. Department of Commercehttps://www.nist.gov/document/2026-nist-handbook-44-appendix-cThe legal-metrology reference for U.S. customary units. Fixes the U.S. liquid gallon at exactly 231 cubic inches and tabulates the full liquid-volume chain (minim → fluid dram → fluid ounce → gill → pint → quart → gallon).
6. Methodology — the partial-fill formulas and liquid densities used on this sitetankvolumecalc.comhttps://tankvolumecalc.com/methodology/Every chart value here comes from a closed-form partial-fill formula, not interpolation: circular segments for cylinders, a piecewise obround model for 275/330 heating-oil tanks, and scaled spherical caps for dished heads. Densities and their bases are tabulated there.
7. ISO 7507-1 — Petroleum and liquid petroleum products: Calibration of vertical cylindrical tanks, Part 1: Manual strapping methodInternational Organization for StandardizationPaid standard — cited by designation; obtain from the publisher.Defines how a tank's capacity table (its “strapping table”) is produced from physical measurement, including corrections for plate thickness, shell expansion and tank tilt. It is the reason a real tank's chart rarely matches naive geometry to the last gallon.

Every linked source above was retrieved and checked on 2026-09-02. Factors quoted as exact are exact by definition in the cited document, not rounded by us.