US Gallons to liters
1 US gal = 3.78541 L, derived from exact unit definitions.
| US gal | L |
|---|---|
| 1 US gal | 3.79 L |
| 5 US gal | 18.93 L |
| 10 US gal | 37.85 L |
| 55 US gal | 208.20 L |
| 100 US gal | 378.54 L |
| 275 US gal | 1,040.99 L |
| 500 US gal | 1,892.71 L |
| 1,000 US gal | 3,785.41 L |
liters = US gallons × 3.785411784Exact. 3.785411784 is not a rounded measurement — it falls out of two definitions that are themselves exact, so you can carry every digit without accumulating error.How to convert US gallons to liters
Multiply by 3.785411784. That is the whole method, and because the factor is exact the only thing you have to decide is where to round — a choice that belongs at the end of the calculation, never in the middle.
- Confirm you have US liquid gallons. The US dry gallon (4.405 L) and the imperial gallon (4.54609 L) are different units that share the word.
- Multiply the gallon figure by 3.785411784.
- Round once, at the end, to the precision your job actually justifies — see the rounding section below.
- Sanity-check the magnitude: litres should be roughly four times the gallon number. If your answer is close to the input, you have divided instead of multiplied.
A 275-gallon heating-oil tank, in litres
- Nominal capacity: 275 US gal
- 275 × 3.785411784 = 1040.98824 L
- Round to the nearest litre: 1041 L
275 US gal = 1,041 L
Nominal capacity is the tank's rated size, not what it holds in service. A 275-gallon tank is normally filled to about 90 % — roughly 940 L — to leave ullage for thermal expansion.
Converting a fuel delivery for an invoice check
- Delivered: 412.6 US gal
- 412.6 × 3.785411784 = 1561.86...
- 1561.86 rounds to 1561.9 L (one decimal, matching the meter's resolution)
412.6 US gal = 1,561.9 L
Do not add decimals your meter cannot produce. A ticket printed to 0.1 gal does not become more accurate by being reported to 0.001 L.
Sizing a metric pump for a US-spec tank
- Tank must empty in 45 min: 1,500 US gal
- 1500 × 3.785411784 = 5678.117676 L
- 5678.12 L ÷ 45 min = 126.2 L/min
1,500 US gal in 45 min = 126.2 L/min ≈ 7.57 m³/h
Where the factor comes from
Two definitions, chained. Neither is a measurement, so neither carries uncertainty.
1 US gallon ≡ 231 in³ (NIST Handbook 44, App. C)
1 inch ≡ 2.54 cm (1959 Yard & Pound Agreement)
1 in³ = 2.54³ = 16.387064 cm³ exactly
231 in³ = 231 × 16.387064
= 3785.411784 cm³
1 litre ≡ 1 dm³ = 1000 cm³ (BIPM SI Brochure)
∴ 1 US gal = 3.785411784 L exactlyThe decimal terminates because 2.54³ terminates and 231 is an integer. That is unusual: most volume conversions on this site do not terminate.The 231 in³ figure is inherited, not invented. It is the old English wine gallon standardised under Queen Anne, adopted by the United States and then frozen into US law, which is why the US gallon and the imperial gallon parted company rather than converging.
Rounding: how much precision do you actually need?
The common shortcuts are fine at small volumes and quietly wrong at large ones. The error is proportional, so it scales with the tank.
| Factor used | Relative error | Error on 275 gal | Error on 20,000 gal |
|---|---|---|---|
| 3.785411784 (exact) | 0 | 0 L | 0 L |
| 3.7854 | −0.00031 % | 0.003 L | 0.24 L |
| 3.785 | −0.011 % | 0.11 L | 8.2 L |
| 3.79 | +0.12 % | 1.3 L | 92 L |
| 3.8 (mental arithmetic) | +0.39 % | 4.0 L | 291 L |
Rule of thumb: 3.785 is enough for anything you can carry, 3.78541 is enough for any tank, and the full factor costs nothing if a calculator is doing the work.
FAQ
How many liters are in a US gallon?
Exactly 3.785411784 L. The value is exact rather than measured: a US gallon is defined as 231 cubic inches, and an inch is defined as 2.54 cm, so the litre figure is pure arithmetic.
Is 3.785 accurate enough?
For almost everything, yes. Truncating to 3.785 understates the result by about 0.011 %, which is 0.1 L on a 275-gallon oil tank and 8 L on a 20,000-gallon storage tank. If either of those matters, use the full factor.
Why is the imperial gallon a different size?
Because it has a different legal definition. The UK Weights and Measures Act 1985 fixes the imperial gallon at 4.54609 litres, while the US gallon descends from the 231-cubic-inch wine gallon. One imperial gallon is about 1.2 US gallons — a 20 % gap that shows up whenever UK, Irish or older Canadian tank specs are read as US figures.
Does the conversion change with temperature?
The conversion does not; the liquid does. 3.785411784 L per gallon is true at any temperature because both units are defined geometrically. What changes is how much mass occupies that volume, which is why fuel is traded on volume corrected to a reference temperature of 60 °F or 15 °C.
What about US dry gallons?
A US dry gallon is about 4.405 L and is used for grain and produce, not liquids. If a spec says just “gallons” for a liquid in a US context, it means US liquid gallons.
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.
- 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.
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.