Fuel Price Converter
Convert a fuel price between per litre, per US gallon and per imperial gallon, and compare two forecourts on the same basis. Handles the 20% gap between the two gallons.
Fuel Price Converter
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- Converts price per volume only. Fuel economy conversion belongs to the Fuel Economy Converter.
- No currency conversion — enter both prices in the same currency.
- Fuels traded by mass, such as LPG and bunker fuel, need a temperature-dependent density and are out of scope.
In short: A US gallon is 3.785411784 litres and an imperial gallon is 4.54609 litres, so the imperial gallon is about 20.0949926% larger. A price quoted per gallon means two materially different things depending on which gallon is meant.
Formula
price per L = price per gallon ÷ litres per gallon
1 US gal = 3.785411784 L · 1 imp gal = 4.54609 L
[('price per L', 'the common basis every quote is reduced to'), ('US gallon', '231 cubic inches exactly, so 3.785411784 L'), ('imperial gallon', '4.54609 L exactly, defined in the UK in 1985'), ('ratio', 'imperial ÷ US = 1.200949925504855')]
Worked Example
- Identify which gallon the price is quoted in — US or imperial. This is the step that goes wrong.
- Divide the price by the litres in that gallon to get a price per litre.
- Multiply by the other gallon's litre count to express it on that basis.
- To compare two forecourts, reduce both to price per litre first.
- To cost a journey, multiply the per-litre price by the consumption in litres per 100 km.
1.75 per litre is 6.62 per US gallon but 7.96 per imperial gallon — the same fuel, the same price, a gap of 1.33 that is entirely an artefact of which gallon is meant. At 7.5 L per 100 km, that 1.75 per litre works out at 13.13 per 100 km.
Strengths & Limits Of This Model
Where this engine is strong
- Both gallon definitions are exact, not rounded
- Reduces every quote to price per litre before comparing
- Shows the cost of a fill and per 100 km at common consumptions
Where it stops
- No currency conversion
- Does not convert consumption figures
Practical Use Cases
Comparing forecourts across a border
Putting a per-litre price and a per-gallon price on the same basis before deciding where to fill.
Reading an American road-trip figure
Converting a US dollar-per-gallon price into a per-litre price that means something locally.
Checking a fleet fuel card statement
Normalising quotes that arrive on different volume bases.
Budgeting a long drive
Turning a pump price into a cost per 100 km at a known consumption.
Sanity-checking an mpg claim
Establishing whether a quoted figure uses the imperial gallon, which flatters it by about a fifth.
Methodology & Editorial Standards
Both gallon definitions are exact: the US gallon is 231 cubic inches, which is 3.785411784 L given the international inch of 25.4 mm, and the imperial gallon is defined directly as 4.54609 L. All conversion runs through price per litre as the single canonical basis, so a per-US-gallon quote and a per-imperial-gallon quote are always reduced before being compared. Fuel prices are shown to three decimals because that is the precision forecourts actually use.
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Fuel Price Converter — 10 Expert FAQs
10 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
Why is a US gallon smaller than an imperial gallon?
They descend from different measures. The US kept the English wine gallon of 231 cubic inches; Britain redefined its gallon in 1824 as the volume of ten pounds of water, later fixed at exactly 4.54609 litres. The imperial gallon is about 20.09% larger, and nothing about the two has converged since.
How many litres in a gallon?
3.785411784 in a US gallon and 4.54609 in an imperial gallon. Both figures are exact by definition rather than measured, which is why they carry so many digits without uncertainty.
Why does my car get better mpg in Britain?
It does not — the gallon is bigger. An imperial mpg figure is about 20.09% higher than the US figure for the identical car and the identical fuel. Any comparison of mpg numbers across the Atlantic has to name which gallon is meant, which is one reason litres per 100 km has largely replaced both.
Is this the same as a fuel economy converter?
No. This page converts a PRICE between volume bases. Converting consumption — mpg to litres per 100 km — is a different calculation with an inverse relationship, and the Fuel Economy Converter handles it.
Why is fuel priced to three decimals?
Because volumes are large. A tenth of a minor unit per litre is five units on a fifty litre fill, and far more across a fleet, so forecourts and wholesalers price to a precision that looks excessive on a single transaction and is not.
How do I work out the cost of a journey?
Multiply your consumption in litres per 100 km by the distance in hundreds of kilometres, then by the price per litre. At 7.5 L per 100 km and 1.75 per litre, 100 km costs 13.13. Full trip budgeting, including tolls and wear, belongs to the Everyday Life calculators.
Does this account for tax?
It converts whatever price you enter, and pump prices normally already include fuel duty and VAT. If you are working from a pre-tax wholesale figure, the conversion still holds — but do not compare a pre-tax quote against a pump price.
Which is cheaper per gallon or per litre?
Neither. They are the same fuel at the same price expressed differently. A price only becomes comparable once both quotes are reduced to the same unit, which is the single thing this page exists to do.
What about pricing by weight?
Some fuels, notably LPG and marine bunker fuel, are traded by mass rather than volume. Converting between them needs a density that varies with temperature and grade, so it is not a fixed factor and is outside this page's scope.
Does temperature affect the volume of fuel?
Yes. Petrol and diesel expand as they warm, so a litre delivered at 25°C contains slightly less energy than a litre at 15°C. Wholesale trade corrects to a reference temperature for exactly this reason; retail pumps generally do not, which is a small but real effect on a hot day.