Convert MPG (UK) to MPG (US) miles per imperial gallon ↔ miles per US gallon Free Online Secure
Type a value in miles per imperial gallon and read it in miles per US gallon at once. The factor is exact by definition, the arithmetic happens in your browser, and nothing is sent anywhere.
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Common values — Convert MPG (UK) to MPG (US) (miles per imperial gallon ↔ miles per US gallon)
| MPG (UK) | MPG (US) |
|---|---|
| 20 | 16.6534836926 |
| 25 | 20.8168546157 |
| 30 | 24.9802255389 |
| 35 | 29.143596462 |
| 40 | 33.3069673852 |
| 50 | 41.6337092314 |
| 60 | 49.9604510777 |
| 70 | 58.287192924 |
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 MPG (US): what an American reader should take from a British road test
British motoring media is followed all over America, on video channels and in magazines: a hot hatch "returned 38 mpg", a luxury saloon "managed 28". Those numbers are in miles per imperial gallon, and an American who compares them with a window sticker is comparing different gallons. The imperial gallon is 4.546 litres and the US gallon 3.785, so a British figure overstates the American one by a fifth. To convert MPG (UK) to MPG (US), multiply by 0.8327: 30 UK mpg is 25.0 US mpg, 45 is 37.5, 60 is 50.0 and 70 is 58.3. Both countries use miles, so the distance is already the same, and only the gallon needs correcting. The calculator above multiplies as you type, and the sections that follow show how to read British figures for cars, motorbikes and electric vehicles.
Below come the rule with examples, short notes on each unit, a side-by-side look and a long series of British motoring cases, ending with the slips people make most. Everything is computed locally in the page. The conversion changes the unit, not the amount of fuel the car actually burns.
How to convert MPG (UK) to MPG (US): multiply by 0.8327
The rule
A US gallon holds 3.785412 litres and an imperial gallon 4.54609, a ratio of 0.832674. For a “convert MPG (UK) to MPG (US)” calculation, take the UK mpg times 0.8327: 22 UK mpg gives 18.3, 38 gives 31.6 and 62 gives 51.6 US mpg. To go the other way, multiply by 1.2009.
Only the gallon changes
Britain and the United States both measure distance in miles, so a mile in one is a mile in the other. The two figures differ by the size of the gallon alone, a constant 16.7 per cent, from the smallest to the largest value. That is why a plain multiplier is enough here, unlike the conversion to litres per 100 km.
Worked examples
A hot hatch at 34 UK mpg is 28.3 US mpg. A diesel estate at 58 UK mpg is 48.3 US mpg. A supercar at 19 UK mpg is 15.8 US mpg, and a small city car at 62 UK mpg is 51.6 US mpg.
A quick sanity test
Expect the US result to be a sixth below the UK figure. A larger number than you began with means 1.2009 was used where 0.8327 belonged.
MPG (UK)
Miles per imperial gallon
The British unit counts miles per imperial gallon of 4.546 litres. It dominates British reviews, adverts and conversation, even though the fuel is sold by the litre and the labels also carry grams of carbon dioxide.
Where it appears
British magazines and video channels, used-car adverts and brochures.
MPG (US)
Miles per US gallon
The American unit counts miles per US gallon of 3.785 litres. It is the language of the EPA window sticker and of American reviews. The US gallon is smaller, so its figures are smaller for the same car.
Where it appears
EPA stickers, American reviews and federal regulations.
UK MPG set beside US MPG
Written in US mpg, the same car comes out a sixth lower than in UK mpg: 40 becomes 33.3, 55 becomes 45.8 and 80 becomes 66.6. The car and its consumption have not changed, only the gallon.
Nothing is lost on the way. The mistake seen most often is taking a British figure for an American one, which makes the car look a fifth more economical than it is.
Where the conversion shows up
Reading a British road test
A British test says "overall 41 mpg, 52 on a gentle run". For an American that is 34.1 and 43.3 mpg. In litres per 100 km, 6.89 and 5.43. When you convert MPG (UK) to MPG (US), remember that British tests often use a fixed real-world route, so the number is nearer to the road than a laboratory one.
Sports and luxury cars
A hot hatch returns 32 to 38 UK mpg, 26.6 to 31.6 US, a sports coupe 24 to 30, 20.0 to 25.0 US, and a supercar 17 to 22 UK mpg, 14.2 to 18.3 US. The figures sound modest to British ears and normal to American ones, since the same car returns the same distance in litres.
Electric cars
British electric cars are rated in miles per kWh. 4.0 miles per kWh is 0.25 kWh per mile, 25 kWh per 100 miles, which is 135 MPGe on the EPA basis of 33.7 kWh per US gallon. Electric figures need no gallon conversion, since there is no gallon in the calculation.
What "true MPG" means
British magazines run every car over the same road route and publish a true figure. A car with an official 52 mpg, 43.3 US mpg, might show 44 true mpg, 36.6 US. This is a gap of 15 per cent, similar to the one between EPA labels and real use, and it is on top of the gallon difference.
Tank size
A British tank of 50 litres is 11.0 imperial gallons or 13.2 US gallons. At 45 UK mpg, 37.5 US mpg, it gives 495 miles either way. Range is not changed by the gallon, because the volume and the mpg are in the same unit and the unit cancels.
Fuel economy rules
The United States regulates fuel economy in mpg for the fleet average, and the European Union regulates carbon dioxide per kilometre. A European fleet at 95 g/km is about 4.1 L/100 km on petrol, 68.7 UK mpg, 57.2 US mpg. Comparing the two systems means turning carbon dioxide into litres and then litres into the right mpg.
A worked example
An American driver wants to compare a British saloon, advertised at 46 UK mpg, with an American one at 35 mpg. The British one is 38.3 US mpg, so it is 9 per cent better, at 6.14 against 6.72 L/100 km. At 12,000 miles a year the British saloon uses 313 US gallons and the American one 343, 30 gallons more, 112 litres. The conversion decides the matter.
The mental shortcut
To convert MPG (UK) to MPG (US) without a calculator, take off a sixth of the British figure. At 48 UK mpg that gives 40, close to the exact 39.97, and at 36 it gives 30 against 29.98. The error is below a tenth of a per cent; for the other direction add a fifth.
Spreadsheet formulas
Put the UK mpg in column A, then =A2*0.832674 in column B returns US mpg and =B2*1.20095 reverses it. A pair of helper columns, =282.481/A2 and =235.215/B2, should both return the same L/100 km as a cross-check.
Rounding in reviews
Reviews print mpg as whole numbers, so 52 UK mpg comes out as 43 US mpg rather than 43.3. Real consumption differs from the published figure by 10 to 20 per cent anyway, and a decimal place would only suggest a precision nobody has.
Landmarks to memorise
Remember that 10 UK mpg = 8.3 US, 20 = 16.7, 30 = 25.0, 40 = 33.3, 50 = 41.6, 60 = 50.0 and 70 = 58.3. With them a mental convert MPG (UK) to MPG (US) takes a moment.
Reference ladder
12 UK mpg: 10.0 US. 25: 20.8. 36: 30.0. 47: 39.1. 58: 48.3. 72: 60.0. With a list of this kind any result can be checked quickly.
Checking by reversing
Test a “convert MPG (UK) to MPG (US)” calculation answer by multiplying it by 1.2009: 39.1 US mpg gives 47.0 UK mpg, so the 47 you started from came through intact. A second sign of a good result is that the US figure sits a sixth below the UK one.
Link to L/100 km and km/L
In 40 UK mpg there are 7.06 L/100 km, 14.16 km/L and 33.3 US mpg. The units differ and the consumption does not, so a “convert MPG (UK) to MPG (US)” calculation only relabels it.
Plug-in hybrid claims
A British plug-in hybrid may be rated 217 mpg, 180.7 US mpg. It is a measure of the test, which counts the electric part of the journey as free. With a flat battery the same car does 40 to 50 UK mpg, 33.3 to 41.6 US mpg. The EPA uses a separate method that gives MPGe and an all-petrol figure.
Two routes to one answer
Go straight by multiplying the UK mpg by 0.8327, or travel via litres per 100 km: 282.481 ÷ UK mpg, then 235.215 ÷ that. If the answers drift apart, a digit slipped somewhere.
Company-car tax and carbon dioxide
In Britain, the tax on a company car depends on its carbon dioxide emissions, not its mpg. A car at 50 UK mpg, 5.65 L/100 km, emits about 130 g/km on petrol, and one at 40 UK mpg, 7.06 L/100 km, about 163 g/km. In US mpg these are 41.6 and 33.3. British drivers therefore know both numbers.
Economy runs and records
Hypermiling and economy-run events report very large figures. A diesel family car driven gently may return 85 UK mpg, 70.8 US mpg, 3.32 L/100 km, in a carefully managed run, against an official 65, 54.1 US. The difference between a record and a normal drive is mostly speed, anticipation and tyre pressure.
Towing a caravan
Towing a caravan can take an estate car from 40 UK mpg, 33.3 US mpg, to 27, 22.5 US mpg. In litres per 100 km that is 7.06 rising to 10.5. For a 500 mile trip, 805 km, the extra is 6.0 imperial gallons, 7.2 US gallons, or 27 litres. Caravan clubs publish both figures.
Lorries and coaches
A heavy lorry returns 8 to 9 UK mpg, 6.7 to 7.5 US, and a coach 9 to 11, 7.5 to 9.2 US. In litres per 100 km that is 31 to 35 for the lorry and 26 to 31 for the coach. Operators think in litres, but British trade press and drivers still talk in mpg.
Campervans
A campervan on a panel-van chassis returns 25 to 32 UK mpg, 20.8 to 26.6 US, and a coachbuilt motorhome 20 to 26, 16.7 to 21.6 US. For a 1,500 mile, 2,414 km, holiday in Europe, the van uses 47 to 60 imperial gallons, 56 to 72 US gallons. Fuel is then one of the main items in the budget.
Cold weather
Economy falls in the cold. A car doing 45 UK mpg, 37.5 US mpg, in summer may do 40 UK, 33.3 US, in winter, a drop of 11 per cent. Short trips with a cold engine can cost another 10 to 20 per cent. British test figures are taken at about 20 °C and do not reflect it.
Tyre pressure
A British car whose tyres are 6 psi, 0.4 bar, below the correct pressure loses 1 to 2 per cent of its economy, so 45 UK mpg, 37.5 US, falls to 44.3, 36.9. The effect is similar in both countries. Pressures are labelled in psi in Britain too, so the owner's manual reads in the same figures as an American one.
Big luxury and sports cars
An old V12 luxury saloon returns 14 to 17 UK mpg, 11.7 to 14.2 US mpg, 16.6 to 20.2 L/100 km, and a supercar in town 12 to 15, 10.0 to 12.5 US. An American collector with a similar V12 would quote 12 to 14 mpg, which is the same car described in the American gallon.
Buying a British car in America
A dealer in the United States who sells a British car will list the consumption from the owner's handbook, often in UK mpg. A buyer who sees "35 mpg" should confirm which gallon is meant. 35 UK mpg is 29.1 US mpg, 8.07 L/100 km, a figure close to many American midsize cars.
Mild hybrids and diesels
A mild-hybrid petrol saloon at 48 UK mpg is 40.0 US mpg, and a diesel estate at 60 UK mpg is 50.0 US mpg. A litre of diesel contains 12 per cent more energy than a litre of petrol, so the diesel is only about 12 per cent ahead in energy terms, not 25. The comparison should be done in litres or in energy.
Fuel and sales rules
Fuel in Britain is sold by the litre, and fuel in the United States by the US gallon. A fill of 50 litres in Britain is 13.2 US gallons. A driver who fills up 13 gallons in America and 50 litres in Britain has bought the same amount. The litre is the unit that links the two systems, which is why the conversion to L/100 km is the safest check.
Land Rovers and four-wheel drives
A Defender 90 diesel returns 22 to 27 UK mpg, 18.3 to 22.5 US, 10.5 to 12.8 L/100 km. A current large four-wheel drive with a diesel six-cylinder returns 30 to 36 UK mpg, 25.0 to 30.0 US. American drivers who see "36 mpg" in a British test for a big SUV should not expect it from a US-spec model.
Classic cars
A classic Mini returns 38 to 48 UK mpg, 31.6 to 40.0 US mpg. A Jaguar E-Type returns 16 to 20 UK mpg, 13.3 to 16.7 US, and a Rolls-Royce Silver Shadow 11 to 14, 9.2 to 11.7 US. US collectors who read old British road tests need the conversion to judge what the car will do on American roads.
Motorcycles
A British middleweight motorcycle returns 55 to 65 UK mpg, 45.8 to 54.1 US, a 125 cc scooter 100 to 110, 83.3 to 91.6 US, and a big adventure bike 40 to 48, 33.3 to 40.0 US. British riders quote mpg so often that the scooter's three-figure number has become normal.
Fuel price per gallon
At 1.50 pounds a litre an imperial gallon costs 6.82 pounds, a US gallon 5.68 pounds. If a pound is worth 1.25 dollars, the US gallon is 7.10 dollars. A car at 40 UK mpg costs 17 pence a mile, and the same car at 33.3 US mpg with the US gallon price also costs 17 pence. The result must be matched with a price in the right gallon.
Cost per mile in cents
At 3.50 dollars a US gallon, a car at 33.3 US mpg, 40 UK mpg, costs 10.5 cents a mile. At 4.20 dollars an imperial gallon the same car at 40 UK mpg costs 10.5 cents a mile too. The gallon cancels when price and mpg use the same one, so there is never a reason to mix them.
Speed limits and consumption
British motorways have a 70 mph limit and many American interstates 65 to 75. A car doing 50 UK mpg, 41.6 US mpg, at 70 mph might do 43 UK mpg, 35.8 US, at 80, about 14 per cent worse. British drivers rarely exceed 80 mph for long, whereas some American states permit 85.
More values for convert MPG (UK) to MPG (US)
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) = 2.49802 MPG (US)
- 7 MPG (UK) = 5.82872 MPG (US)
- 9 MPG (UK) = 7.49407 MPG (US)
- 12 MPG (UK) = 9.99209 MPG (US)
- 15 MPG (UK) = 12.4901 MPG (US)
- 20 MPG (UK) = 16.6535 MPG (US)
- 35 MPG (UK) = 29.1436 MPG (US)
- 40 MPG (UK) = 33.307 MPG (US)
Common slips with a “convert MPG (UK) to MPG (US)” calculation
The factor the wrong way round
Going from UK to US lowers the number by a sixth. If 40 turned into 48, the factor for the opposite direction, 1.2009, was used.
Not knowing the gallon
An advert saying just "mpg" may be US or UK. Cars made for North America use the US gallon, British cars the imperial one. When in doubt, ask for litres per 100 km.
Ranking cars from mixed sources
A car at 45 UK mpg is not better than one at 40 US mpg, since the first is 37.5 US mpg. Put everything in one unit before you compare.
Short answers
How do I convert MPG (UK) to MPG (US)?
Take the UK mpg times 0.8327.
What is 40 UK mpg in US mpg?
It is 33.3 US mpg.
What is 60 UK mpg in US mpg?
It is 50.0 US mpg.
What is 30 US mpg in UK mpg?
It is 36.0 UK 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 L/100km, Convert km/L to MPG (US), Convert L/100km to MPG (US), Convert MPG (US) to km/L, Convert km to mi, Convert mi to km, Convert °C to °F, Convert °F to °C. Going the other way is covered by Convert MPG (US) to MPG (UK).
To sum up, a “convert MPG (UK) to MPG (US)” calculation needs one multiplication by 0.8327 and a unit beside the answer. The figure is worked out on your own device, without registration or upload.