Convert MPG (UK) to L/100km miles per imperial gallon ↔ litres per 100 kilometres Free Online Secure
Type a figure in miles per imperial gallon and read it in litres per 100 kilometres at once. These two run opposite ways — one counts fuel per distance, the other distance per fuel — so the page divides rather than multiplies.
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Convert to litres per 100 kilometres
Common values — Convert MPG (UK) to L/100km (miles per imperial gallon ↔ litres per 100 kilometres)
| MPG (UK) | L/100km |
|---|---|
| 20 | 14.1240468166 |
| 25 | 11.2992374533 |
| 30 | 9.41603121106 |
| 35 | 8.07088389519 |
| 40 | 7.0620234083 |
| 50 | 5.64961872664 |
| 60 | 4.70801560553 |
| 70 | 4.0354419476 |
Where these units come from
Fuel economy is said in two opposite ways. Litres per 100 km asks how much fuel a fixed distance costs; miles per gallon and kilometres per litre ask how far a fixed amount of fuel goes. One is the reciprocal of the other, which is why this page multiplies and divides rather than scaling. Europe settled on litres per 100 km in the 1970s precisely because it is linear in the thing you actually pay for: halve the number and you halve the fuel. The United States kept miles per gallon, and Britain kept it too but with the imperial gallon — a fifth larger — so the same car scores about 20% better in British figures than in American ones without a single part having changed.
Where you meet them
These numbers decide which car gets bought, what a fleet costs to run, how company-car tax is assessed in several countries, and whether a long trip is worth driving rather than flying. They also appear on every new-car window sticker, measured on a standard test cycle rather than on a real road — which is why the figure is best used to compare one car with another, not to predict what your own week will cost.
Questions people ask
Why does the same car get a better mpg figure in Britain than in America?
Because the gallons are different. The imperial gallon is 4.54609 litres and the US gallon 3.785411784 litres, about a fifth smaller. A car that travels 30 miles on a US gallon travels the same distance on less than a British gallon, so its British figure comes out around 36 mpg. Nothing about the car changed; only the size of the container did. Always check which gallon a figure means before comparing two cars across the Atlantic.
Why is litres per 100 km considered the better measure?
Because miles per gallon flatters improvements at the top and hides them at the bottom. Going from 10 to 15 mpg saves twice as much fuel over the same distance as going from 30 to 50 — which is the opposite of what the numbers look like. Litres per 100 km has no such trap: the saving is simply the difference between the two figures. This is why fuel-saving decisions are easier to judge in litres per 100 km, even where mpg is what everyone quotes.
Is the answer exact?
Where both units are defined in terms of one another by whole numbers, yes — the page says so above the figure, and the only rounding is in how many digits are shown. Where the ratio has no finite decimal, the page shows twelve significant digits and says the relation is approximate rather than pretending otherwise.
Does anything I type leave my device?
No. The arithmetic runs in your browser; nothing is uploaded and there is no server to upload it to. Load the page once and it keeps working with the network switched off.
MPG (UK) to L/100 km: old imperial figures in a metric Commonwealth
In Canada, Ireland, Australia, New Zealand and South Africa fuel is sold by the litre, and modern cars carry labels in litres per 100 km. But the imperial gallon left a long shadow. Grandparents still say "thirty miles to the gallon", old manuals quote mpg, classic-car adverts give imperial figures, and a British magazine read on a phone does the same. All of those numbers are in miles per imperial gallon of 4.546 litres, so they need a different constant from the American one. To convert MPG (UK) to L/100km, divide 282.5 by the mpg: 20 mpg is 14.1 L/100 km, 35 mpg is 8.07 L/100 km, 50 mpg is 5.65 L/100 km and 70 mpg is 4.04 L/100 km. The calculator above divides as you type, and the sections that follow show how those figures are used across the Commonwealth.
Below come the rule with examples, short notes on each unit, a side-by-side look and a long series of everyday cases from Canada to New Zealand, ending with the slips people make most. Everything is computed locally in the page. Real fuel use depends on speed, load and weather.
How to convert MPG (UK) to L/100km: divide 282.5 by the mpg
The rule
An imperial gallon holds 4.54609 litres and a mile is 1.609344 km, which makes 1 mpg equal to 282.481 L/100 km, so the consumption in litres per 100 km is 282.481 divided by the mpg. For a “convert MPG (UK) to L/100km” calculation, take 282.481 / 28 = 10.1 L/100 km, 282.481 / 42 = 6.73 L/100 km and 282.481 / 65 = 4.35 L/100 km. The rule works in both directions.
The curve behind the numbers
More mpg means fewer litres, but not in proportion. From 20 to 40 mpg consumption halves, from 14.1 to 7.06 L/100 km, and from 40 to 80 it halves again, to 3.53. Equal gains in mpg are therefore worth less and less in litres, which is why a conversion is more informative than the original number.
Worked examples
An old saloon at 24 mpg uses 11.8 L/100 km. A compact at 44 mpg uses 6.42, a diesel hatchback at 62 mpg uses 4.56, and a pickup at 19 mpg uses 14.9 L/100 km.
A quick sanity test
Multiply mpg by L/100 km and expect about 282.5: a car of 44 mpg and 6.42 L/100 km gives 282.5. A result near 235 means the American constant slipped in, which is the commonest error here, and then the “convert MPG (UK) to L/100km” calculation needs repeating.
Miles per imperial gallon
The Commonwealth's inheritance
Miles per imperial gallon was the standard in Britain and in much of the Commonwealth until the switch to metric measures. It lives on in conversation, in old documents and in British motoring media.
Where it appears
Classic-car adverts, old manuals, British reviews and talk between older drivers.
Litres per 100 kilometres
The metric label
Fuel per distance is the unit of the label in most Commonwealth countries today. A smaller figure is better, and multiplying by the price per litre gives the cost of a trip directly.
Where it appears
Canadian EnerGuide labels, Australian and New Zealand fuel guides, and European data sheets.
MPG (UK) against L/100 km
Counted in litres per 100 km, a car looks the opposite way round to mpg: 25 mpg turns into 11.3, 50 into 5.65 and 100 into 2.82. Double the mpg and the litres halve, while the product of every pair stays at 282.5.
Nothing is lost on the way. The slip seen most often is the US gallon, smaller by 17 per cent, which would put the result 20 per cent too high.
Where the conversion shows up
Canada
Canadians moved to litres in the 1970s, but many drivers who grew up with imperial mpg still think in it, and cars in the US are priced in US gallons. A Canadian label of 8.1 L/100 km is 34.9 imperial mpg and 29.0 US mpg. A “convert MPG (UK) to L/100km” calculation for imperial mpg and a second one with the American constant keep the two apart at the border.
Ireland and the old documents
Used-car adverts in Ireland and the UK often give imperial mpg for older models, while newer cars carry litres per 100 km. A 2008 saloon advertised at 38 mpg uses 7.43 L/100 km, which makes it comparable with a 2020 model labelled 6.8. Check that both come from the same test cycle before drawing conclusions.
Classic and collector cars
A 1960s saloon that returns 25 mpg uses 11.3 L/100 km and a sports car at 20 mpg 14.1. Collectors who drive few miles do not worry about the cost, but the figure helps when planning a long rally or the capacity of the fuel stops on it.
US and Canadian fuel economy side by side
A car rated 30 US mpg, 7.84 L/100 km, is 36.0 imperial mpg. Canadian reviews of vehicles built for both markets give L/100 km, and a Canadian driver crossing the border sees US pumps in gallons. Dividing by the right constant for each country, 235.2 or 282.5, prevents a 20 per cent mistake.
Plug-in hybrid labels
A plug-in hybrid may carry a label of 188 mpg, 1.5 L/100 km, because the test assumes a charged battery for part of the distance. On petrol alone the same car does 42 to 50 mpg, 5.6 to 6.7 L/100 km. The label tells nothing about a long trip where the battery is flat after 50 km.
Motorcycles
A touring motorcycle does 45 to 55 mpg, 5.1 to 6.3 L/100 km, a 125 cc scooter 100 to 110 mpg, 2.6 to 2.8 L/100 km, and a 1,000 cc sports bike 35 to 42 mpg, 6.7 to 8.1 L/100 km. Riders in the Commonwealth often quote mpg because the habit survived in bike magazines.
Fuel for the journey
A tank of 55 litres, 12.1 imperial gallons, at 45 mpg, 6.28 L/100 km, gives 545 miles, 877 km. At 30 mpg, 9.42 L/100 km, it gives 363 miles, 584 km. On a long drive across a country with sparse fuel stops, the number of litres per 100 km tells you whether the tank reaches the next one.
Cold starts and short trips
A cold engine uses far more fuel than a warm one. In the first 3 km consumption can nearly double: a car of 52 mpg, 5.43 L/100 km, may use 10 L/100 km, 28.2 mpg, over that stretch. On trips of 3 to 5 km the real figure is 8 to 10 L/100 km, much higher than the label.
Speed on the open road
A petrol car doing 41 mpg, 6.89 L/100 km, at 60 mph, 97 km/h, drops to 36 mpg, 7.85 L/100 km, at 70 mph, 113 km/h, a 14 per cent rise for a 17 per cent rise in speed. On 1,000 km that is 10 litres. Setting cruise control slightly lower costs only a few minutes on a long trip.
A worked example
You inherit a car with a service history in imperial mpg: 31 mpg for town driving and 47 for the motorway. In metric terms that is 9.11 and 6.01 L/100 km. If you drive 70 per cent in town and 30 per cent on the open road, the average is 8.18 L/100 km, 34.5 mpg. A “convert MPG (UK) to L/100km” calculation on each figure gives the data for the budget.
The mental shortcut
To convert MPG (UK) to L/100km without a calculator, divide 280 by the mpg and add 1 per cent. At 40 mpg that gives 7, plus 0.07, or 7.07, close to the exact 7.06. Starting from 300 is easier but runs about 6 per cent high.
Spreadsheet formulas
Put the imperial mpg in column A, then =282.481/A2 in column B returns L/100 km, and the same formula pointed the other way returns mpg. =A2*0.354006 gives km/L and =A2*0.832674 US mpg for cross-checks.
Rounding old figures
Old manuals print mpg to the whole number, sometimes to the nearest five. Quote L/100 km to one decimal at most: 33 mpg is 8.6. Anything finer would claim an accuracy that a 50-year-old road test never had.
Landmarks to memorise
Remember that 20 mpg = 14.1 L/100 km, 25 = 11.3, 30 = 9.4, 35 = 8.1, 40 = 7.1, 50 = 5.6, 60 = 4.7 and 70 = 4.0. With them a mental convert MPG (UK) to L/100km takes a moment.
Australia and New Zealand
Both countries converted to metric in the 1970s and now use L/100 km on labels. A driver over 60 may still remember a family car doing 25 mpg, 11.3 L/100 km. Used imports from Japan add a third unit, kilometres per litre. A figure of 15 km/L is 6.67 L/100 km and 42.4 imperial mpg.
Reference ladder
16 mpg: 17.7 L/100 km. 24 mpg: 11.8. 29 mpg: 9.74. 36 mpg: 7.85. 48 mpg: 5.89. 66 mpg: 4.28. 110 mpg: 2.57. With a list of this kind any result can be checked quickly.
Checking by reversing
Test a “convert MPG (UK) to L/100km” calculation answer by dividing 282.5 by it: 7.85 L/100 km gives 36.0 mpg, so the 36 you started from came through intact. A second sign of a good result is that the product is close to 282.5.
Link to US mpg and km/L
In 40 imperial mpg there are 7.06 L/100 km, 14.2 km/L and 33.3 US mpg. The US figure is 0.8327 of the imperial, the ratio of the gallons. The units differ and the consumption does not, so a “convert MPG (UK) to L/100km” calculation only relabels it.
Two routes to one answer
Go straight with 282.481 divided by the mpg, or travel via US mpg: multiply by 0.8327 and divide 235.215 by the result. A further path uses km/L: mpg × 0.354, then 100 ÷ that. If the answers drift apart, a digit slipped somewhere.
Hire cars on holiday
A hire contract in Ireland or New Zealand may quote an old-style "about 40 mpg", which is 7.06 L/100 km. A road trip of 1,500 km then needs 106 litres, 23 imperial gallons, and at 2.00 dollars a litre costs 212 dollars. A “convert MPG (UK) to L/100km” calculation before the trip turns the mpg in the leaflet into a budget in the currency you will be spending.
Mild hybrids and start-stop
A mild-hybrid or start-stop system can save 3 to 8 per cent in town, taking a car from 40 mpg, 7.06 L/100 km, to 42 to 43 mpg, 6.6 to 6.7 L/100 km. The effect shows in the town figure of the label far more than in the motorway one, because engine-off coasting and idling are the main sources of saving.
South Africa and India
South Africa uses L/100 km, and India uses kilometres per litre. A car sold in both markets with 6.5 L/100 km is 15.4 km/L and 43.5 imperial mpg. Imperial mpg is rare in those countries but appears in older British-made manuals, so the constant 282.5 is useful there too.
Old workshop manuals
Workshop manuals of the 1960s and 1970s state fuel consumption in imperial mpg at constant speeds. A saloon rated 33 mpg at 56 mph, 90 km/h, uses 8.56 L/100 km, and 27 mpg at 70 mph, 113 km/h, uses 10.5 L/100 km. The figures are from steady-speed tests rather than modern cycles, and a “convert MPG (UK) to L/100km” calculation makes them readable.
Light commercial vehicles
A panel van does 32 to 40 mpg, 7.1 to 8.8 L/100 km. A 3.5 tonne chassis cab does 22 to 28 mpg, 10.1 to 12.8 L/100 km. A tradesperson who drives 25,000 km a year at 8.8 L/100 km burns 2,207 litres, while a van at 7.1 burns 1,766, which at 1.80 dollars a litre is 794 dollars a year.
Taxis and minicabs
A diesel black cab does 28 to 33 mpg, 8.6 to 10.1 L/100 km, and a hybrid saloon minicab 58 to 68 mpg, 4.2 to 4.9 L/100 km. A driver covering 80,000 km a year saves about 4,200 litres by moving from the first to the second. That helps explain why hybrids spread so quickly through the taxi trade.
Motorhomes and caravans
A motorhome on a van chassis does 22 to 28 mpg, 10.1 to 12.8 L/100 km. An SUV of 35 mpg, 8.07 L/100 km, towing a caravan falls to 22 mpg, 12.8 L/100 km. On a 1,000 km holiday trip that is 47 litres more, or about 10 imperial gallons.
Buses and coaches
A city bus does 5 to 7 mpg, 40.4 to 56.5 L/100 km, a school bus 8 to 11, 25.7 to 35.3, and a coach 9 to 11, 25.7 to 31.4. Transit operators track litres per 100 km, since the figure adds up over a fleet, while mpg is an informal measure used by drivers.
Real-world testing
Magazines test cars on a fixed route and publish true mpg. A car with an official 52 mpg, 5.43 L/100 km, might return 44 mpg, 6.42 L/100 km, which is 18 per cent worse than the label. In the best cases the gap is only 5 per cent, and in the worst more than 30.
More values for convert MPG (UK) to L/100km
A longer list of conversions
If the value you need is not in the first list, these further conversions may be close enough to read off directly:
- 3 MPG (UK) = 94.1603 L/100km
- 7 MPG (UK) = 40.3544 L/100km
- 9 MPG (UK) = 31.3868 L/100km
- 12 MPG (UK) = 23.5401 L/100km
- 15 MPG (UK) = 18.8321 L/100km
- 20 MPG (UK) = 14.124 L/100km
- 35 MPG (UK) = 8.07088 L/100km
- 40 MPG (UK) = 7.06202 L/100km
Common slips with a “convert MPG (UK) to L/100km” calculation
Using the US constant
For imperial mpg use 282.5. The American 235.2 gives a result 17 per cent lower than the right one, a typical slip when a British magazine is read in North America.
Multiplying instead of dividing
The conversion is a division of a constant by the figure. Multiplying 40 by 282 gives 11,280, which is not a consumption of any vehicle.
Averaging mpg
The average of two mpg figures is not the average consumption. Convert to litres per 100 km, average those, and convert back if you wish.
Short answers
How do I convert MPG (UK) to L/100km?
Take 282.5 and divide it by the mpg.
What is 40 UK mpg in L/100 km?
It is 7.06 L/100 km.
What is 30 UK mpg in L/100 km?
It is 9.42 L/100 km.
What is 8 L/100 km in UK mpg?
It is 35.3 mpg.
Is my number sent anywhere?
No, everything is computed in the browser.
More pages and a wrap-up
Other fuel-economy conversions are listed in Convert MPG (UK) to km/L, Convert MPG (UK) to MPG (US), Convert MPG (US) to L/100km, Convert km/L to L/100km, Convert L/100km to MPG (US), Convert km to mi, Convert mi to km, Convert °C to °F, Convert °F to °C. Going the other way is covered by Convert L/100km to MPG (UK).
To sum up, a “convert MPG (UK) to L/100km” calculation needs one division of 282.5 by the mpg and a unit beside the answer. The figure is worked out on your own device, without registration or upload.