Litres to Gallons Calculator

How the litres to gallons conversion works

A litre is a metric unit of volume equal to one cubic decimetre (1 dm³ = 0.001 m³). The UK (imperial) gallon and the US gallon are both non-metric units labelled "gallon" but are defined differently and are not interchangeable — the imperial gallon is larger. The calculator multiplies the volume in litres by the exact factor for each gallon type and by the UK pint factor, displaying all three alongside for direct comparison.

The exact conversion factors

The imperial gallon is defined as exactly 4.54609 litres — a definition set by the Weights and Measures Act 1985 and aligned with the international definition. The factor used here is therefore 1 ÷ 4.54609 = 0.219969... UK gallons per litre. The US liquid gallon is defined as exactly 231 cubic inches; because one inch is 0.0254 m exactly, one US gallon is 231 × 0.0254³ × 10⁶ = 3.785411784 litres. The factor is 1 ÷ 3.785411784 = 0.264172... US gallons per litre. The UK pint is one-eighth of an imperial gallon, so 4.54609 ÷ 8 = 0.568261 litres per pint, giving 1 ÷ 0.568261 = 1.7598 pints per litre. All factors are exact definitions; no approximation enters the conversion arithmetic.

The imperial gallon versus the US gallon

The imperial gallon (4.54609 L) is approximately 20% larger than the US gallon (3.78541 L). This distinction is practically important in UK construction and plumbing. A water tank described as "100 gallons" in an older UK document holds 454.6 litres; the same description in a US document holds only 378.5 litres. Coverage figures on older UK paint tins labelled in gallons refer to imperial gallons. The calculator shows both to remove ambiguity when the source of a gallon figure is unknown.

What a UK gallon actually measures

The imperial gallon was originally defined as the volume of 10 pounds of distilled water at 62 °F (≈ 16.7 °C) under standard pressure. The modern definition — 4.54609 litres exactly — superseded that temperature-dependent definition and is the basis for all current UK trade and regulatory purposes. The imperial pint, one-eighth of a gallon, is 568.261 ml; it remains the legal measure for draught beer and cider in UK licensed premises.

Worked examples

1 litre converts to 0.220 UK gal (0.264 US gal, 1.76 pt). A 10-litre paint tin is 2.200 UK gal (2.642 US gal, 17.60 pt). A 25-litre water container is 5.499 UK gal (6.604 US gal, 43.99 pt). Each result follows directly from the exact factor with no intermediate rounding step.

Where litres and gallons appear in UK construction practice

Water storage tanks and hot-water cylinders in the UK are sized in litres on current product data sheets, but older installations and BS 417 copper tanks carry capacities in imperial gallons. Boiler and heat-pump hot-water cylinders are rated in litres; domestic cold water storage tanks historically ranged from 18 gallons (82 litres) to 50 gallons (227 litres). Converting between the two is a routine step when replacing a pre-metric tank or specifying compatible pipework.

Paint sold in the UK is labelled in litres (250 ml, 1 L, 2.5 L, 5 L, 10 L), but coverage figures on older tins and US-origin product data sheets appear in square feet per gallon. A quick litre-to-gallon conversion clarifies whether a coverage rate on an imported or older product applies to a UK-gallon figure or a US-gallon figure — the two differ by about 20%, which affects the area a given tin covers.

Rainwater harvesting systems are sized in litres in current UK guidance (CIRIA C765); tank sizes derived from older rule-of-thumb guides may quote imperial gallons. Garden-irrigation system capacities and borehole pump flow rates sometimes appear in US gallons per minute in equipment from North American manufacturers.

Gallons and UK plumbing regulations

Part G of the Building Regulations (Sanitation, Hot Water Safety and Water Efficiency) sets water consumption limits in litres per person per day. Water-storage requirements for domestic hot-water cylinders are expressed in litres in current practice. Imperial gallons appear in pre-1970 Building Regulations and in historic British Standards still referenced for existing installations.

Precision and rounding

The conversion factors are exact definitions, so result precision is limited only by the volume entered and by display rounding. The calculator shows UK gallons to three decimal places (to the nearest 0.001 gal ≈ 4.55 ml), US gallons to three decimal places (≈ 3.79 ml), and UK pints to two decimal places (≈ 5.68 ml). For tank sizing and material coverage purposes, two or three decimal places in gallons is more than adequate resolution.

Using this alongside other BuildMetricLab tools

Once a volume is confirmed in litres, it converts directly to cubic metres (÷ 1,000) for use in concrete, excavation, and pool-volume calculators. The pool volume calculator returns results in litres and cubic metres; the cubic metres to cubic yards converter handles plant-capacity cross-checks. All BuildMetricLab tools run entirely in the browser — no sign-up, no data sent anywhere, and the formula is shown on the page so the arithmetic can be audited.