550 Gallon Underground Oil Tank chart

How to stick this tank

Underground tanks are sticked through the fill pipe. Lower the stick until it rests on the tank bottom, then read the wet line — but remember the fill pipe riser adds length above the tank: your liquid depth is measured from the stick bottom to the wet line only, and it can never exceed the tank diameter. Two pro habits: smear water-finding paste on the bottom few inches of the stick once a season (it changes color if groundwater is intruding), and stick before and after a metered delivery once — if the chart agrees with the metered gallons, you've confirmed the tank size.

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 16.70 gallons; at the narrowest it is 3.40 gallons — a factor of 4.9×. 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:

• Tank tilt is designed in. Buried tanks are commonly set with a deliberate slope so product drains toward one end. The chart assumes level, so a sloped tank reads high or low depending on which end the fill pipe is at. ISO 7507 and the API calibration standards include explicit tilt corrections for this reason.
• Water bottoms. Water accumulates under the fuel and is measured separately with water-finding paste. Subtract the water depth's volume from the total before you call the rest product.
• The drop tube and riser add height that is not tank. Measure to the tank bottom, and know how far below grade that is — a stick that bottoms out on a riser shoulder will read consistently short and look like a slow leak.
• Thermal movement between the delivery and the gauge. Fuel delivered warm and gauged cold has shrunk. On a 1,000 gallon tank a 15 °F drop is roughly 7 gallons of apparent loss with nothing actually missing.

The standards behind this tank

Buried fuel tanks sit inside a federal regulatory programme, 40 CFR Part 280, and a chart like this one is part of how compliance is demonstrated. Under § 280.43(a), inventory control must be capable of detecting a release of 1.0 % of flow-through plus 130 gallons in a month, and the gauging equipment must read the full height of the tank to the nearest one-eighth of an inch. That is the specification your stick and your chart together have to meet.

Manual tank gauging is allowed as the sole release-detection method only for tanks of 550 gallons or less nominal capacity, and for some 551–1,000 gallon tanks that meet the diameter criteria in § 280.43(b). Larger tanks need it in combination with, or replaced by, another method. State programmes approved under 40 CFR Part 281 are often stricter than the federal floor.

Construction is to UL 58 for steel USTs (or UL 1746 for jacketed steel), and installation to NFPA 31 where the tank feeds oil-burning equipment. For a capacity table you can defend, calibrate under ISO 7507 rather than computing from nominal dimensions.

Where this chart's geometry comes from

Dimensions modelled: 42 x 92 in variant per supplier gauge charts. Geometry yields 551 gal. 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 550 gal; geometry as modelled 551.8 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 underground fuel-oil tank in service.

1. 40 CFR § 280.43 — Methods of release detection for tanksU.S. Environmental Protection Agency, via the electronic Code of Federal Regulationshttps://www.ecfr.gov/current/title-40/chapter-I/subchapter-I/part-280/subpart-D/section-280.43The federal rule that makes tank charts a compliance instrument rather than a convenience. Inventory control must detect a release of 1.0 % of flow-through plus 130 gallons per month; gauging equipment must read the full tank height to the nearest one-eighth of an inch; manual tank gauging is allowed as the sole release-detection method only for tanks of 550 gallons or less (and some 551–1,000 gallon tanks meeting the diameter criteria).
2. 40 CFR Part 280 — Technical Standards and Corrective Action Requirements for Owners and Operators of Underground Storage TanksU.S. Environmental Protection Agency, via the electronic Code of Federal Regulationshttps://www.ecfr.gov/current/title-40/chapter-I/subchapter-I/part-280The whole federal UST programme: design and construction standards (§ 280.20), release detection (Subpart D), operator training and closure. State programmes approved under Part 281 may be stricter.
3. 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.
4. 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.
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. 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.
7. 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.

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.