Tank charts, inch by inch.

How to use a tank chart without fooling yourself

A tank chart answers one question: given a liquid depth measured from the inside bottom, how much is in the tank? Everything that goes wrong with charts goes wrong in the gap between that sentence and what people actually do.

• Measure from the inside bottom, not from a convenient edge. Not the fill-pipe rim, not the top of a riser, not the outside of the shell. On a buried tank the distance from grade to tank bottom is a number you should have written down at installation.
• Keep the stick vertical. An angled fill pipe does not excuse an angled stick. Ten degrees off vertical reads about 1.5 % long; twenty degrees reads 6 % long.
• Don't interpolate linearly on a round tank. In a horizontal cylinder the middle inches hold far more than the end inches, so averaging two distant chart rows is systematically wrong. Every chart here has a reader that computes the exact value instead.
• Half depth is not half volume on any tank with curved ends. Each chart page states the depth at which half that tank's volume actually sits.
• Subtract the water bottom. Water is denser than fuel and sits underneath. Your stick reads total depth; the chart converts total depth to total volume. Find the water line with water-finding paste and take it off before you call the rest product.

What a computed chart is, and what it isn't

Every value on these pages comes from a closed-form partial-fill formula applied to a stated geometry — circular segments for cylinders, a piecewise obround model for 275 and 330 gallon heating-oil tanks, and scaled spherical caps for dished heads. There is no interpolation and no curve fitting, and the tolerances are enforced by automated tests before each build. The methodology page shows the derivations.

That makes these charts exact for the geometry stated. It does not make them a calibration. A real tank has corner radii, internal ribs, plate thickness, a fabrication tolerance and usually a degree or two of tilt, and the difference against a manufacturer's own chart is typically 1–3 %. For operations, ordering and reconciliation that is fine. For custody transfer or 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 MPMS chapters, with corrections for plate thickness, shell expansion and tilt.

Where charts become a legal requirement

For underground fuel tanks, gauging is not optional record-keeping. Under 40 CFR § 280.43(a) inventory control must be capable of detecting a release of 1.0 % of flow-through plus 130 gallons in a month, deliveries must be reconciled against receipts, and the gauging equipment must resolve the full height of the tank to the nearest one-eighth of an inch. Manual tank gauging is permitted as the sole release-detection method only for tanks of 550 gallons or less nominal capacity, and for some 551–1,000 gallon tanks meeting the diameter criteria in § 280.43(b). State programmes approved under 40 CFR Part 281 are often stricter.

Propane is the exception on this site: a propane vessel is a sealed pressure vessel and must never be opened or stuck. Its chart pages exist so you can cross-check a suspect float gauge — which reads percent of water capacity, not gallons of propane — against a delivery ticket.

Sources and standards

These are the documents behind the units, the codes and the calibration practice referenced across the chart library. Individual chart pages cite the subset that applies to that tank.

1. 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).
2. Special Publication 811, Appendix B.8 — Factors for Units Listed AlphabeticallyNational Institute of Standards and Technologyhttps://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b8NIST's master table of conversions into SI. Factors printed in boldface are exact by definition rather than measured or rounded — which is how you tell a defined unit from an approximated one.
3. 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).
4. 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.
5. 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.
6. Manual of Petroleum Measurement Standards (MPMS) — Ch. 1 “Vocabulary”, Ch. 11.1 “Temperature and Pressure Correction Factors”, Ch. 12.1 “Calculation of Static Petroleum Quantities”American Petroleum Institute (with ASTM D1250 / ISO 91 volume correction tables)Paid standard — cited by designation; obtain from the publisher.The industry standard for turning a gauged tank volume into a traded quantity: observed volume, gross standard volume at 60 °F, and net standard volume after sediment and water. A unit conversion is only the first step of that chain.
7. 29 CFR § 1910.110 — Storage and handling of liquefied petroleum gases (Table H-23, minimum distances)U.S. Occupational Safety and Health Administration, via the electronic Code of Federal Regulationshttps://www.ecfr.gov/current/title-29/subtitle-B/chapter-XVII/part-1910/subpart-H/section-1910.110Federal separation distances for LP-gas containers, by water capacity: under 125 gal — 10 ft above ground; 125–250 gal — 10 ft; 251–500 gal — 10 ft and 3 ft between containers; 501–2,000 gal — 25 ft (reducible to 10 ft for a single container of 1,200 gal water capacity or less, if it is at least 25 ft from any other LP-gas container over 125 gal); 2,001–30,000 gal — 50 ft.
8. NFPA 58 — Liquefied Petroleum Gas Code (separation distances, Table 6.4.1.1; filling limits, Ch. 7)National Fire Protection AssociationPaid standard — cited by designation; obtain from the publisher.The model code most US states adopt for propane installations, and the one your local inspector is most likely working from. It is not identical to OSHA's Table H-23 — notably for containers of 125 gal water capacity and under — so confirm which is enforced locally. NFPA publishes free read-only access to its codes at nfpa.org.
9. 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.
10. 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.
11. 49 CFR § 178.504 — Standards for steel drums (and § 178.502, identification codes)U.S. Pipeline and Hazardous Materials Safety Administration, via the electronic Code of Federal Regulationshttps://www.ecfr.gov/current/title-49/subtitle-B/chapter-I/subchapter-C/part-178/subpart-L/section-178.504The current federal standard for steel drums. Codes are 1A1 (non-removable head) and 1A2 (removable head); openings over 3 inches make a drum removable-head by definition. The legacy DOT-17E designation was superseded by these UN performance-oriented standards.
12. 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.