What this calculator does
A kilogram is a unit of mass and a gallon is a unit of volume, so converting between them is not a fixed ratio the way converting kilometres to miles is. The two are only linked through density: how much mass a given volume of the specific substance actually has. Water is the easy case, since 1 kilogram of water occupies almost exactly 1 litre, but oil, milk, flour and most other materials sit at a different density and need their own figure.
This calculator converts kilograms to gallons or gallons to kilograms using a density you can edit, defaulting to water at 1 kg per litre. It also lets you choose between US and UK (imperial) gallons, which are meaningfully different sizes: a US gallon is about 3.785 litres, while a UK gallon is about 4.546 litres, roughly 20 per cent larger.
The formula
The value is first converted to litres using the density supplied (litres = kg ÷ density), then litres are converted to gallons using the chosen gallon definition. Going the other way, gallons are converted to litres, then litres to kilograms by multiplying by density.
| Term | Meaning |
|---|---|
| Density | Mass per unit volume of the specific substance, in kilograms per litre. Water is 1 kg/L; other liquids and solids vary. |
| US gallon | Equal to 3.785411784 litres, the gallon used in the United States. |
| UK (imperial) gallon | Equal to 4.54609 litres, used in the United Kingdom and some Commonwealth countries, about 20 per cent larger than a US gallon. |
The inputs explained
| Field | What to enter |
|---|---|
| Value | The amount to convert, in kilograms or in the chosen gallon type, depending on the direction selected. |
| Convert | Whether you are converting kilograms to gallons, or gallons back to kilograms. |
| Gallon type | Which gallon definition to use. US and UK gallons differ by about 20 per cent, so picking the wrong one gives a noticeably wrong answer. |
| Density (kg/L) | The density of the substance being converted, in kilograms per litre. Leave at 1 for water; look up or measure the correct figure for anything else. |
When to use it
Shipping or storing water
Water sits at a density of 1 kg/L, so 10 kg of water is very close to 2.64 US gallons or 2.20 UK gallons, and the default settings need no adjustment.
Working with a denser or lighter liquid
Motor oil, for instance, is lighter than water at around 0.88 kg/L. The same 10 kg of oil takes up more volume than 10 kg of water, so entering the correct density before converting matters if the answer needs to be accurate rather than approximate.
Reconciling a US recipe or spec sheet with UK units
A US supplier quoting a gallon figure and a UK buyer expecting imperial gallons are not talking about the same volume. Converting both back to kilograms via a shared density is one way to check the figures actually match.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
Kilograms of water converted to both gallon types
The same mass of water, shown in both US and UK gallons, at a fixed water density.
How density changes the gallons produced by a fixed 10 kg
The same 10 kg mass converted at different densities, showing why the substance matters.
Questions
Why is there no single kg to gallons conversion factor?
Because a kilogram measures mass and a gallon measures volume. The relationship between them depends on the density of whatever is being measured, which varies from substance to substance, so a universal conversion factor would only be correct for one specific material.
What density should I use for water?
Water is close enough to 1 kg per litre for almost all practical purposes at everyday temperatures, which is the default here. It shifts very slightly with temperature, but not enough to matter outside laboratory work.
Is a US gallon the same as a UK gallon?
No. A US gallon is about 3.785 litres and a UK (imperial) gallon is about 4.546 litres, roughly 20 per cent larger. Always check which one a source is using before comparing figures.
Where do I find the density of a specific substance?
Product data sheets, safety data sheets (SDS) and reference tables for common liquids and materials usually list density in kg/L or kg/m³ (divide by 1000 to get kg/L). If none is available, weighing a known volume gives a rough figure directly.
For a plain kilograms-to-litres conversion without the gallon step, see the Kg to Litres Converter. For everyday kitchen liquids like milk and honey, the grams to millilitres converter uses preset densities instead of a manual figure.