Liters to Gallons Converter

Litres and gallons measure the same thing, volume of liquid, but the conversion between them depends on which gallon you mean. The US liquid gallon is exactly 3.785411784 litres, the UK imperial gallon is exactly 4.54609 litres, and the two differ by roughly 20%. Picking the wrong one for a fuel-economy figure, a brewing recipe, an aquarium dose, or a chemical dilution is one of the most common conversion mistakes in everyday calculations. This tool handles both gallon definitions with the exact NIST SP 811 conversion factors, cross-displays the alternative gallon and the millilitre equivalent, and supports bidirectional conversion (litres → gallons, or gallons → litres) from the same input.

How to Use

1. Pick a direction using the four buttons at the top: Litres → US gal, Litres → UK gal, US gal → Litres, UK gal → Litres.
2. Type your value into the labelled input. The label updates to match the chosen direction (Litres or Gallons).
3. Click Convert (or press Enter). The result panel shows the converted value, the cross-unit conversion (US gal → UK gal or vice versa), and the millilitre equivalent.
4. Use the cross-display for sanity checks: if you convert 1 L and read 0.264 US gal, the UK gal should be 0.220 (not the same number, the two gallon definitions differ by 20%).
5. For values that round to zero in the target unit (a few drops in US gallons, say), the millilitre field shows the precise value.

The Formula

The two conversion factors are stored as exact decimal constants, no rounding, no approximation:

1 L = 0.26417205235815 US gal       (US liquid gallon)
1 L = 0.21996924829909 UK gal       (UK imperial gallon)
1 US gal = 3.785411784 L             (exact, by definition)
1 UK gal = 4.54609 L                 (exact, by 1985 redefinition)

To convert from litres to a gallon, multiply by the appropriate factor. To convert from a gallon to litres, divide by the same factor. The cross-display computes the other gallon from the source value using the ratio of the two factors (US gal / UK gal ≈ 1.200949, or UK gal / US gal ≈ 0.832674). Millilitres are always litres × 1000, exact by definition of the SI litre.

The exact litre-to-gallon factors above are taken from NIST SP 811 (Guide for the Use of the SI Units, 2008 edition, Appendix B.8), which is the authoritative US reference for conversion factors between SI and non-SI units. The same factors appear in the BIPM SI Brochure (9th edition, 2019) and in ASTM E380.

Worked Examples

1. One litre to US gallons. 1 L → 0.26417205235815 US gal. The single-digit answer most pocket calculators give (0.26) is only accurate to 3 significant digits, accurate enough for a car's fuel tank, not for a pharmaceutical dose. For volume work in the lab, use the full 14-digit factor.

2. Five litres to UK gallons. 5 L → 1.09984624149545 UK gal (5 × 0.21996924829909). Five litres of petrol at a UK forecourt price rounds to about 1.10 UK gallons. UK petrol pricing has been quoted per UK gallon since 1985; pre-1985 it used the same gallon but with the previous definition.

3. US gallon to litres. 1 US gal → 3.785411784 L. This is the standard denominator for US fuel-economy figures (MPG = miles per US gallon). To convert MPG to L/100 km, divide 235.215 by the MPG figure; to convert L/100 km to MPG, divide 235.215 by the L/100 km figure.

4. UK gallon to litres. 1 UK gal → 4.54609 L. The UK imperial gallon was redefined by the Weights and Measures Act 1985 to be exactly this volume; the previous definition (the volume of 10 pounds of water at a specific temperature) gave a slightly different value. Modern UK fuel-economy figures use the exact redefinition.

5. Reverse sanity check. 3.785411784 L × 0.26417205235815 = 1.00000000000000 US gal. The round trip is exact to the precision of IEEE 754 double-precision floats (about 15 decimal digits), so a US gallon expressed in litres and back is bit-identical to the original.

6. Cross-display. 1 US gallon = 1.200949 UK gallons, and 1 UK gallon = 0.832674 US gallons. The 20% difference between the two gallon definitions is real and is a common source of error when reading old recipes (US recipes typically use US gallons, UK recipes use UK gallons) or when comparing fuel-economy figures published in different countries.

Where It Shows Up

Litres and gallons show up everywhere liquid volume is measured. Cooking recipes in the US use cups, fluid ounces, quarts, and gallons; UK recipes use millilitres and litres (since metrication in the 1960s-1970s); recipes from older British books use the imperial gallon. Fuel economy is quoted as MPG (miles per US gallon) in the United States and as MPG (miles per UK gallon) in the United Kingdom until 1985 and in the same units after; the two figures are not directly comparable because the underlying gallons differ by 20%. Aquarium dosing, brewing, winemaking, and chemical dilution all involve liquid volume and all need both unit systems. Industrial chemistry, pharmaceutical compounding, and laboratory work are all metric (litres and millilitres), but consumer products often carry US customary units on the label. Water bills, milk deliveries, and bulk fuel pricing are quoted in the local gallon.

The cross-display of millilitres is particularly useful for chemical dilution calculations, where the final concentration is usually expressed in grams per litre or moles per litre but the starting material is often measured in fluid ounces or gallons.

Common Mistakes

1. Using the wrong gallon. A US gallon is 3.785 L; a UK gallon is 4.546 L. Using the wrong one makes the answer 20% off, a serious error for chemical dosing, fuel-economy comparison, or recipe scaling. Always check which gallon your source means: US sources almost always use the US gallon; UK sources post-1985 use the exact UK gallon.

2. Rounding too early. Most pocket calculators show 0.26 for one litre in US gallons. The true answer is 0.26417205235815. Rounding to two decimal digits is fine for casual conversion but loses precision when the value is used as an intermediate step (e.g. computing concentration from a US-gallon measurement). Carry at least four significant digits through any calculation that will be multiplied or divided.

3. Confusing fluid ounces with weight ounces. A US fluid ounce of water weighs roughly 1.043 ounces (avoirdupois), not exactly one ounce. The difference is small (4.3%) but matters for shipping calculations, recipe costing, and any context where the volume-to-weight ratio matters. A US gallon of water weighs about 8.345 pounds at standard temperature and pressure.

4. Mixing US and UK in the same calculation. If a recipe says "1 gallon of stock plus 500 mL of wine" and you use US gallons for one and UK gallons for the other, the final volume is wrong by 20%. Standardise on one gallon definition before starting the calculation. The convention is US gallon in the Americas, UK gallon in the UK, and either (with explicit declaration) in scientific publications.

5. Forgetting that "gallon" can mean other things. The US has a "dry gallon" (a third definition, exactly 4.40488377086 L, used for some agricultural products), the UK had a "wine gallon" and a "beer gallon" before the imperial gallon was standardised, and oil is priced per "barrel" (42 US gallons, ~159 L) rather than per gallon. If your source says "gallon" without qualification, ask which one, don't assume.

Frequently Asked Questions

Q: How many litres in a US gallon? A: Exactly 3.785411784 litres. The US gallon is defined by the US Bureau of Standards (now NIST) as exactly 231 cubic inches, which works out to 3.785411784 litres at the exact conversion 1 inch = 2.54 cm. This definition has been in force since the 19th century and has not changed.

Q: How many litres in a UK gallon? A: Exactly 4.54609 litres. The UK imperial gallon was redefined by the Weights and Measures Act 1985 to be exactly this volume. Before 1985, it was defined as the volume of ten pounds of water at a specific temperature, which gave a value of approximately 4.54609 litres anyway; the 1985 redefinition made the exact value official.

Q: Which gallon does my country use? A: The United States, Liberia, and Myanmar use the US liquid gallon for everyday volume measurement. The United Kingdom, Canada (for some purposes), and most Commonwealth countries use the UK imperial gallon for legacy recipes and some historical fuel-economy figures. Most countries that have officially metricated use litres exclusively; recipes and consumer products are labelled in litres, and fuel is priced per litre. For scientific work, the litre is the universal unit and the gallon is a secondary definition.

Q: How do I convert miles per gallon to litres per 100 kilometres? A: For US gallons: divide 235.215 by the MPG figure. For example, 30 MPG (US) = 235.215 / 30 = 7.84 L/100 km. For UK gallons: divide 282.481 by the MPG figure. For example, 30 MPG (UK) = 282.481 / 30 = 9.42 L/100 km. The two figures differ by about 20% because the underlying gallons differ by 20%.

Q: What is the difference between a US dry gallon and a US liquid gallon? A: The US has two gallons: the liquid gallon (231 cubic inches, 3.785411784 L, used for most liquid measurements) and the dry gallon (exactly 4.40488377086 L, used for some dry goods like grain). The dry gallon is a vanishingly rare unit today; if you see "gallon" in a US context, assume the liquid gallon unless the context is explicitly dry goods.

Q: How accurate is this converter? A: The converter uses the exact NIST SP 811 factors, which are exact to all 14 significant digits shown. The arithmetic is done in IEEE 754 double-precision floating point, which is accurate to about 15 significant digits, so the result is exact to the limit of the input representation. For values at the extremes of the JavaScript Number range, subnormal precision may apply; for any realistic liquid volume, the result is exact.

Q: Can the Liters to Gallons Converter, L ↔ US gal + UK gal + mL be used for professional or commercial purposes?ed for professional or commercial purposes? A: Yes, the Liters to Gallons Converter, L ↔ US gal + UK gal + mL provides mathematically correct results that are suitable for professional, commercial, and educational use. For the Liters to Gallons Converter, L ↔ US gal + UK gal + mL, For the Liters to Gallons Converter, L ↔ US gal + UK gal + mL, For high-stakes applications (medical, legal, financial), verify results with a domain expert. For the Liters to Gallons Converter, L ↔ US gal + UK gal + mL, the Liters to Gallons Converter, L ↔ US gal + UK gal + mL formulas used are well-established and validated against reference standards.

How often are the Liters to Gallons Converter, L ↔ US gal + UK gal + mL formulas updated? ↔ US gal + UK gal + mL formulas updated? For the Liters to Gallons Converter, L ↔ US gal + UK gal + mL, A: the Liters to Gallons Converter, L ↔ US gal + UK gal + mL formulas are based on established scientific, mathematical, or industry-standard references and rarely require updates. When standards change (e.g., new physical constants, revised tax brackets, updated standards), the Liters to Gallons Converter, L ↔ US gal + UK gal + mL is updated to reflect the current authoritative source. For the Liters to Gallons Converter, L ↔ US gal + UK gal + mL, Each calculator's references section lists the specific sources used.

References

• NIST SP 811, Guide for the Use of the SI Units, 2008 ed., Appendix B.8, the authoritative US reference for conversion factors between SI and non-SI units. The exact factors 1 L = 0.26417205235815 US gal and 1 L = 0.21996924829909 UK gal are taken from this document.
• BIPM SI Brochure, 9th ed., 2019, Section 2.3.3, the international definition of the litre and its relationship to cubic decimetres (1 L = 1 dm³ exactly).
• Weights and Measures Act 1985 (UK), the statute that redefined the UK imperial gallon to be exactly 4.54609 litres.
• ASTM E380, Standard Practice for the Use of the International System of Units (SI), the US industry standard for SI usage and conversion factors.
• NIST Handbook 44, Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices, 2024 ed., the US regulatory document covering commercial measurement devices, including fuel pumps and milk containers that deliver by the gallon.