US Gallons to cubic meters
1 US gal = 0.00378541 m³, derived from exact unit definitions.
| US gal | m³ |
|---|---|
| 100 US gal | 0.3785 m³ |
| 275 US gal | 1.0410 m³ |
| 500 US gal | 1.8927 m³ |
| 1,000 US gal | 3.7854 m³ |
| 5,000 US gal | 18.9271 m³ |
| 10,000 US gal | 37.8541 m³ |
cubic meters = US gallons × 0.003785411784Exact. This is the gallon-to-litre factor divided by 1000, and it terminates for the same reason: 231 is an integer and 2.54³ terminates.How to convert US gallons to cubic meters
Multiply by 0.003785411784, or convert to litres and divide by 1000 — same operation. Cubic metres are what you want on an engineering drawing, in a tank calibration table produced to ISO 7507, or in any submission to a regulator outside the United States.
- Multiply the gallon figure by 0.003785411784.
- Check the magnitude: cubic metres should be roughly 1/264 of the gallon figure — a 1,000-gallon tank is just under 4 m³.
- Quote to a sensible number of figures. Tank capacities are rarely known better than three or four significant figures, whatever the arithmetic produces.
A 10,000-gallon fire-water tank
- 10000 × 0.003785411784 = 37.85411784
- Quote as 37.85 m³ (four figures)
10,000 US gal = 37.85 m³
A 275-gallon heating oil tank
- 275 × 0.003785411784 = 1.0409882…
- Round to 1.041 m³ = 1,041 L
275 US gal = 1.041 m³
A 20,000-gallon tanker load, for a shipping document
- 20000 × 0.003785411784 = 75.708 m³
- Also 75,708 L, or 75.71 t if the product is 1.00 kg/L
20,000 US gal = 75.71 m³
Volume converts exactly; mass does not. Multiplying by density is a separate step and depends on the product's temperature — see the liquid weight tables.
Where the factor comes from
1 US gal = 231 in³ × (0.0254 m/in)³
1 in³ = 0.0254³ = 0.000016387064 m³ exactly
231 in³ = 231 × 0.000016387064
= 0.003785411784 m³ exactlyBecause both the inch and the gallon are defined exactly, the metric value of a gallon is exact too — a fact worth remembering when a datasheet implies the conversion is approximate.Rounding
0.003785 is 0.011 % low; 0.00379 is 0.12 % high; 0.0038 is 0.39 % high, which on a 100,000-gallon tank farm is 1.5 m³ of phantom capacity. Use at least six significant figures for anything documented.
FAQ
How many cubic meters is a gallon?
Exactly 0.003785411784 m³. Both the gallon (231 cubic inches) and the inch (2.54 cm) are defined exactly, so the metric value of a gallon is exact rather than measured.
How many cubic meters is a 275-gallon tank?
1.041 m³, or 1,041 litres. That is why a nominal 1,000-litre IBC is marketed in the US as a 275-gallon tote — the shell is built slightly oversize.
Should I quote m³ or litres?
Litres for anything under about 10 m³, cubic metres above that. Both are exact against the gallon, and 1 m³ is exactly 1,000 L, so the choice is presentational.
Does this convert tank weight too?
No. It converts volume only. To get mass you multiply by density at the working temperature, which varies by product and is the step where most cross-unit errors actually occur.
Sources and standards
Every factor on this page is traced to the document that defines it. Where a value is exact, it is exact because the cited standard makes it so — not because we rounded it well.
- 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).
- Refinement of Values for the Yard and the Pound — Federal Register Doc. 59-5442 (24 FR 5348, 1 July 1959)National Bureau of Standards; scan hosted by NOAA's National Geodetic Surveyhttps://www.ngs.noaa.gov/PUBS_LIB/FedRegister/FRdoc59-5442.pdfThe International Yard and Pound Agreement, signed by the United States, United Kingdom, Canada, Australia, New Zealand and South Africa. Fixes the yard at exactly 0.9144 m, from which the inch follows as exactly 25.4 mm. Every inch-to-metric volume factor on this site descends from this one page.
- The International System of Units (SI), 9th edition (SI Brochure)Bureau International des Poids et Mesures (BIPM)https://www.bipm.org/en/si-brochure-9The defining document for the SI, maintained by the treaty organisation that owns the definitions. The litre is exactly one cubic decimetre — 10⁻³ m³ — and is a unit accepted for use with the SI rather than an SI unit itself.
- 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.
- 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.