330 Gallon Oil Tank (Vertical) chart

How to stick this tank

Remove the fill cap or the gauge fitting on top of the tank. Lower a clean, dry stick straight down until it gently touches the tank bottom — don't jab, sediment lives there. Hold it vertical for a second, lift it out, and read the wet line. That measurement, from the bottom of the stick to the wet/dry boundary, is the depth you enter above. If your stick goes in through an angled fill pipe, make sure the stick itself ends up vertical inside the tank, or the reading will run long.

What one inch is worth on this tank

An inch is not an inch on this tank. At the widest point one inch of depth is 8.50 gallons; at the narrowest it is 2.10 gallons — a factor of 4.0×. That is exactly why interpolating linearly between two distant chart rows goes wrong, and why the reader above computes the value rather than averaging neighbours.

Why your reading may not match this chart

The arithmetic on this page is exact for the geometry stated below. The disagreements you will actually see come from the tank and the measurement, not the maths — in roughly this order of size:

• The tank is not perfectly plumb. A 275 sitting on settled legs or an uneven pad leans, and the stick then reads long on the low side. Half an inch of lean across the width is easily a few gallons.
• Sludge and water on the bottom. Water is denser than oil and sits underneath. Your stick reads total depth; the chart converts total depth to total volume. If two inches of that is water, two inches of your reading is not fuel.
• Corner radii and internal ribs. The obround model here is exact for the stated geometry, but a real welded tank has corner radii and internal stiffeners that remove a little volume — typically 1–3 % against a manufacturer's own chart.
• The stick is not vertical. Fill pipes on 275s are often offset or angled. A stick 10° off vertical reads about 1.5 % long; 20° off reads 6 % long.

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.

Where this chart's geometry comes from

Dimensions modelled: Highland Tank gauge chart book (27 x 44-1/4 x 72). Every value in the table is computed from that geometry with a closed-form partial-fill formula — a circular or obround segment for the shell, plus scaled spherical caps where the vessel has dished heads. No interpolation, no curve fitting, no lookup tables. The derivations and the automated tolerance tests that gate each build are on the methodology page.

Nominal capacity 330 gal; geometry as modelled 321.5 gal. Where a manufacturer publishes a chart for your specific tank, that chart describes your tank and this one describes the standard geometry — prefer theirs when the two disagree and the number matters.

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.