Unit converter
Imperial Gallons to Liters Converter
Turn imperial gallons into litres for older British measurements and fuel records. The exact factor is 1 imperial gal = 4.54609 l, the value used in `units.ts` for the UK gallon. This conversion appears in miles-per-gallon fuel economy, classic car logbooks, heating oil notes, and old domestic boiler manuals that list tank draw, burner rate, or annual use in gallons. It is specifically the imperial gallon, historically used in the UK, not the smaller US liquid gallon seen in American fuel and grocery contexts.
1 imperial gallon = 4.5461 liters
Common imperial gallons to liters values
| Imperial gallons | Liters |
|---|---|
| 1 gal | 4.5461 l |
| 2 gal | 9.0922 l |
| 5 gal | 22.7305 l |
| 10 gal | 45.4609 l |
| 20 gal | 90.9218 l |
| 50 gal | 227.3 l |
| 100 gal | 454.61 l |
How to convert
- Confirm the gallon figure is imperial, especially if the source is a UK car, boiler, or fuel tank record.
- Multiply the number of imperial gallons by 4.54609 to convert the volume to litres.
- Use the litre result when comparing with modern invoices, pump receipts, or tank capacity labels.
- To reverse the calculation, divide litres by 4.54609 and read the answer as imperial gallons.
- A fast estimate is to multiply gallons by 4.5, then add about 1 percent for a closer litre figure.
litres = imperial gallons * 4.54609
The imperial gallon is defined by the litre value used here. Multiplying the count of imperial gallons by 4.54609 gives the equivalent volume in litres. Dividing a litre amount by 4.54609 produces imperial gallons.
- imperial gal
- the starting volume in imperial gallons
- 4.54609
- litres in one imperial gallon
Worked example
An old heating oil note showing 250 imperial gallons is 250 multiplied by 4.54609, giving 1136.5225 litres. If a modern refill quote is listed in litres, that old note describes a little over 1,136.5 l of oil rather than a 250 l tank.
Key facts
- One imperial gallon contains 8 imperial pints.
- A 10 imperial gallon fuel entry equals 45.4609 l.
- The imperial gallon is larger than the US liquid gallon by 0.760678216 l.
- Old UK boiler and oil tank paperwork may use imperial gallons even when current deliveries are invoiced in litres.
Tips
- When reading old car manuals, check whether mpg means UK imperial mpg or US mpg before comparing economy.
- For heating oil, convert historic gallon records to litres before estimating delivery costs.
- Keep the exact factor in spreadsheets and round only the final litre total.
Frequently asked questions
How many litres in 1 imperial gallon?+
One imperial gallon is exactly 4.54609 l in this calculator.
Is an imperial gallon the same as a US gallon?+
No. An imperial gallon is 4.54609 l, while a US liquid gallon is 3.785411784 l. That makes the imperial gallon about 20 percent larger.
Why do UK fuel economy figures use miles per gallon?+
UK car culture kept miles per imperial gallon for fuel economy even after fuel sales moved to litres. Converting gallons to litres helps compare old mpg records with modern litre-based costs.
How do I convert a boiler consumption rate in gal per hour?+
Multiply the imperial gallons per hour by 4.54609. The result is litres per hour, which can then be compared with pump, nozzle, or fuel delivery figures.
Things to watch
- A US gallon conversion will understate an imperial gallon volume, so do not use American fuel tables for UK records.
- Small rounding differences can become visible on large oil tanks or annual fuel totals.
Sources
- Weights and Measures Act 1985, Schedule 1 · UK National Archives
- The International System of Units (SI Brochure) · BIPM
Last updated: 2026-01-01
Conversions use internationally defined factors. Provided for general use; verify critical measurements independently.