Tank sizes & dimensions.

Three different numbers, all called "capacity"

Almost every argument about tank size is really an argument about which of these three figures someone is quoting.

• Nominal rating. The trade label — "275 gallon", "55 gallon". It is a name, chosen for being memorable and round. Nothing obliges it to match anything.
• Geometric capacity. What the stated dimensions actually hold, brim full, computed exactly. This is the figure in each size table here, and it is frequently a few percent away from the label in either direction.
• Usable capacity. What you can actually put in and get out. Subtract the ullage kept for thermal expansion, the dead volume below the outlet, and for propane the 80 % filling limit. On a propane vessel this is the number that matters and it is never the one on the nameplate.

The nameplate governs for anything built to a listing standard — an ASME propane vessel, a UL 80 oil tank, a UN-marked drum or IBC. For those, the stamped or moulded capacity is authoritative and a tape measure is a cross-check, not a correction.

Dimensions that decide whether a tank fits

Capacity is rarely the constraint. These are:

• The delivery route. Doorway width, stair diagonal, turning radius in a corridor. Measure the route before the tank arrives.
• Overall height including legs and fittings — and then enough clearance above the fill port to lift a stick out of it.
• Regulated clearances. For propane these are set by water capacity, not by fill level, and they differ between OSHA's Table H-23 and NFPA 58. For oil storage above the SPCC thresholds, secondary containment has to hold the largest single container plus freeboard.
• Floor loading. Contents weight over the tank's own footprint, compared against what the structure is designed for. This is the constraint people most often skip, and the one that is most expensive to discover late.

How the figures on these pages are produced

Dimensions are the standard trade geometry for each class, stated on every page so you can check them against your own tank. Capacities are computed from those dimensions with exact partial-fill formulas — see the methodology page — and they match the corresponding chart pages value for value. Liquid weights use the reference densities tabulated on the methodology page, near 60–70 °F; a 10 °F swing moves a hydrocarbon density by roughly 0.4 %, so treat weights as indicative rather than exact.

Where an individual manufacturer's tank differs from the standard geometry, the manufacturer's data sheet describes your tank and these pages describe the class. Prefer theirs whenever the two disagree and the number matters.

Sources and standards

These are the documents behind the units, the listings and the siting rules referenced across the dimension library. Individual size 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. 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.
4. 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.
5. ASME Boiler and Pressure Vessel Code, Section VIII, Division 1 — Rules for Construction of Pressure VesselsAmerican Society of Mechanical EngineersPaid standard — cited by designation; obtain from the publisher.Stationary propane containers are ASME vessels. The nameplate stamps water capacity, design pressure and the manufacturer's data — and the nameplate, not a tape measure, is the authoritative capacity for a pressure vessel.
6. 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.
7. 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.
8. 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.
9. 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.
10. 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.
11. 49 CFR Part 178 — Specifications for Packagings (Subpart N: Intermediate Bulk Containers)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-178Design, construction, marking and periodic retest requirements for IBCs. The UN marking moulded into a tote's bottle records its design type, packing group, test date and rated capacity — read it before trusting a nominal gallon figure.
12. 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.
13. International Residential Code, Table R301.5 — Minimum uniformly distributed live loadsInternational Code Council (free read-only access at codes.iccsafe.org)https://codes.iccsafe.org/s/IRC2021P2/chapter-3-building-planning/IRC2021P2-Pt03-Ch03-SecR301.5Residential floors are designed to 40 lb/ft² live load in habitable rooms other than sleeping rooms, and 30 lb/ft² in sleeping rooms. A filled aquarium concentrates far more than that over its own footprint, which is why the comparison is worth doing before siting one upstairs.
14. 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.