Convert MPG (US) to MPG (UK) miles per US gallon ↔ miles per imperial gallon Free Online Secure
Type a value in miles per US gallon and read it in miles per imperial 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 (US) to MPG (UK) (miles per US gallon ↔ miles per imperial gallon)
| MPG (US) | MPG (UK) |
|---|---|
| 15 | 18.0142488826 |
| 20 | 24.0189985101 |
| 25 | 30.0237481376 |
| 30 | 36.0284977651 |
| 35 | 42.0332473927 |
| 40 | 48.0379970202 |
| 50 | 60.0474962752 |
| 60 | 72.0569955303 |
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 (US) to MPG (UK): the same car looks 20 per cent better in Britain
A midsize crossover rated 28 mpg in an American review is described as 33.6 mpg in a British one. Nothing about the car has changed: the engine, the weight and the fuel it burns are the same. The difference is the gallon. The US gallon holds 3.785 litres and the imperial gallon 4.546, so a car that covers 28 miles on a US gallon covers 33.6 miles on an imperial one. To convert MPG (US) to MPG (UK), multiply by 1.2009: 20 US mpg is 24.0 UK mpg, 35 is 42.0, 45 is 54.0 and 60 is 72.1. The calculator above multiplies as you type, and the sections below explain why the factor is what it is and what it means for expatriates, car shoppers and readers of motoring magazines on both sides of the Atlantic.
The page gives the rule with worked examples, a profile of each unit, a comparison and a long run of cross-Atlantic cases, followed by the usual slips. The calculation runs in your browser and nothing you type is sent anywhere. The conversion changes only the unit, not the real fuel use of the car.
How to convert MPG (US) to MPG (UK): multiply by 1.2009
The rule
The imperial gallon divided by the US gallon is 4.54609 / 3.785412 = 1.200950. To convert MPG (US) to MPG (UK), multiply by 1.2009: 18 US mpg gives 21.6, 30 gives 36.0 and 52 gives 62.5 UK mpg. To go from UK to US mpg, multiply by 0.8327 or divide by 1.2009.
Why a plain factor works here
Both units measure distance per volume of fuel, so they stay in proportion. This is different from converting to litres per 100 km, which turns the figure upside down and needs a constant divided by the mpg. Here every value scales by exactly 20 per cent, from the lowest to the highest.
Worked examples
A saloon at 26 US mpg is 31.2 UK mpg. A pickup at 19 US mpg is 22.8 UK. A hybrid at 55 US mpg is 66.1 UK, and a compact at 36 US mpg is 43.2 UK mpg.
A quick sanity test
The UK figure should come out one fifth higher than the US figure. If a “convert MPG (US) to MPG (UK)” calculation gave a lower number than you started with, you multiplied by 0.8327 instead of 1.2009.
MPG (US)
Miles per US gallon
The American unit counts miles travelled per US gallon of 3.785 litres. It is the unit of the EPA label and of American motoring writing, and it is used in Canada for US-market cars.
Where it appears
EPA labels, American reviews and US fuel-economy regulations.
MPG (UK)
Miles per imperial gallon
The British unit counts miles per imperial gallon of 4.546 litres. It is used in Britain, in Ireland for older cars and in British motoring media, although fuel is sold by the litre in all of these places.
Where it appears
British reviews, used-car adverts and manufacturer brochures in the UK.
US MPG set beside UK MPG
One US mpg is 1.2009 UK mpg, so the British number is a fifth larger. 25 US mpg is 30.0 UK, 40 is 48.0 and 55 is 66.0. The car, the road and the fuel bill are identical.
The conversion is exact. The commonest trap is reading a British figure as an American one, which makes the car look a fifth more economical than it is.
Where the conversion shows up
Shopping across the Atlantic
An expatriate moving from London to Toronto or Texas compares a British car at 48 mpg with an American one at 38. The American one converts to 45.6 UK mpg, so it is only 5 per cent worse. In litres, 5.89 L/100 km against 6.19. A “convert MPG (US) to MPG (UK)” calculation stops one number from being read as the other.
Reading magazines on both sides
A British magazine publishes a test return of 36 mpg for a hatchback, and an American magazine 30 mpg for the same model. Both are 7.84 L/100 km. Test routes differ, but the gallon alone accounts for a fifth of the apparent gap, which is the first thing to take out.
Rental cars
A British family renting a minivan in Florida sees "up to 28 mpg" in the brochure. That is 33.6 UK mpg, 8.40 L/100 km, so a 1,000 mile, 1,609 km, trip uses 36 US gallons, 136 litres, or 30 imperial gallons. Calculating in litres avoids the confusion over which gallon.
How the two gallons arose
The US gallon descends from the English wine gallon of 231 cubic inches, defined in 1707. The imperial gallon was fixed in 1824 as the volume of ten pounds of water, about 277.4 cubic inches, and since 1985 as exactly 4.54609 litres. The United States never adopted the 1824 gallon, so the two have gone separate ways for 200 years.
Heavy vehicles
A heavy American truck at 6.5 US mpg, 36.2 L/100 km, is 7.8 UK mpg. A city bus at 3.5 US mpg, 67.2 L/100 km, is 4.2 UK. For haulage firms the figure that matters is litres per 100 km, since fuel is bought by the litre or the US gallon and mpg is only a convenient comparison.
Tank sizes
A 14 US gallon tank holds 53 litres, which is 11.7 imperial gallons. At 30 US mpg it gives 420 miles, 676 km, and at 36 UK mpg the same tank gives 420 miles again, since both volume and mpg change together. Range does not depend on the gallon, which is why it is the safest figure to compare.
City, highway and combined
An American label shows 21 city, 29 highway and 24 combined. In UK mpg these are 25.2, 34.8 and 28.8, or 11.2, 8.11 and 9.80 L/100 km. The EPA combined figure weights city driving 55 per cent and highway 45 per cent, so it is not the plain average of the other two.
A worked example
You see a hatchback at 31 US mpg in an American advert and another at 36 UK mpg in a British one. The first is 37.2 UK mpg and the second 30.0 US mpg. The American one is 3 per cent better, at 7.59 against 7.85 L/100 km. No litres are needed to see it.
The mental shortcut
To convert MPG (US) to MPG (UK) in your head, add a fifth. For 30 US mpg, 30 plus 6 is 36, against the exact 36.03. For 45, 45 plus 9 is 54, against 54.04. The error is under 0.1 per cent. To go back, subtract a sixth of the UK figure.
Spreadsheet formulas
With the US mpg in column A, put =A2*1.200950 in column B for UK mpg. The reverse is =B2*0.832674. As a cross-check, =235.215/A2 gives L/100 km for the US value and =282.481/B2 gives it for the UK value, and the two must agree.
Rounding in adverts
Mpg figures are quoted as whole numbers, so 28 US mpg is 34 UK mpg, not 33.63. The test itself is accurate to about 3 to 5 per cent, so decimals are meaningless. Round to the nearest whole number.
Landmarks to memorise
10 US mpg is 12.0 UK. 20 is 24.0. 30 is 36.0. 40 is 48.0. 50 is 60.0. 60 is 72.1. 70 is 84.1. With these landmarks nearly every mental convert MPG (US) to MPG (UK) is possible.
Reference ladder
13 US mpg: 15.6 UK. 22: 26.4. 29: 34.8. 34: 40.8. 43: 51.6. 58: 69.7. A table like this lets you test a calculator output at a glance.
Checking by reversing
To check a “convert MPG (US) to MPG (UK)” calculation result, multiply the answer by 0.8327. If 34 US mpg gave 40.8 UK mpg, then 40.8 × 0.8327 = 34.0. A second test is size: the UK figure must be a fifth larger than the US one.
Pints, quarts and ounces
The same gap appears at every level. A US pint is 16 fluid ounces, 473 ml, and an imperial pint 20 fluid ounces, 568 ml. A US quart is 946 ml and an imperial quart 1,137 ml. Both gallons contain 8 pints, so the ratio 1.2009 applies to every unit in the family, and the beer in a pint glass differs across the ocean.
Link to L/100 km and km/L
30 US mpg is 7.84 L/100 km, 12.75 km/L and 36.0 UK mpg. 40 UK mpg is 7.06 L/100 km, 14.16 km/L and 33.3 US mpg. These express the same consumption, and a “convert MPG (US) to MPG (UK)” calculation just swaps the label.
Two routes to one answer
You can multiply by 1.2009 directly, or go through litres: divide 235.215 by the US mpg to get L/100 km, then divide 282.481 by that. If the routes disagree, a digit was copied wrongly.
Reading odometer and speedometer too
A British car shows miles and mph, so its history and its mpg refer to miles. A Canadian or Irish car shows kilometres. When you convert consumption, make sure the distance is the same. A 40 mpg UK car on a 100 km trip uses 7.06 litres, whereas the same distance in miles, 62.1 miles, uses 1.55 imperial gallons.
Ireland, Malta and Cyprus
Ireland, Malta and Cyprus drive on the left and import many British cars. Their older adverts give imperial mpg, while newer labels are in litres per 100 km. A car advertised at 42 mpg is 6.73 L/100 km and 35.0 US mpg, which helps if a relative in America asks how it compares with theirs.
The Caribbean
Several Caribbean islands have both British and American traditions. Used cars arrive from the United States, Japan and Britain, and sellers quote whichever unit the car came with. A vehicle sold at "30 mpg" may thus be 25 mpg in the other system. Asking for the origin of the number saves a wrong purchase.
Racing and classic events
Rally and endurance events publish fuel figures in different units depending on the organisers. A classic rally car using 14 UK mpg, 20.2 L/100 km, is 11.7 US mpg. Planning fuel stops needs the figure in the same gallon as the tank, which is why teams use litres on the stopwatch.
Why the gap never closes
Both systems have stayed with their gallon for generations. Efforts to move American labels to litres per 100 km have met resistance, and the British keep mpg on the dashboard though the pump is metric. Readers who follow cars in both countries will go on meeting the 20 per cent gap, so the factor 1.2009 is a permanent part of the hobby.
Canada's habit
Canada used the imperial gallon until it converted to metric in the 1970s. Older Canadian cars and conversations use imperial mpg, while American-built cars carry US mpg. A Canadian car at 28 imperial mpg, 10.1 L/100 km, is 23.3 US mpg. The modern EnerGuide label avoids it by using L/100 km. The conversion still matters for the used market.
American trucks in Britain
American pickups sold in the UK are marketed with US figures. A truck at 17 mpg US, 13.8 L/100 km, is 20.4 mpg UK. A diesel pickup at 24 mpg US, 9.80 L/100 km, is 28.8 mpg UK. Buyers who see the American number should convert before they compare the truck with a British van at 35 mpg, 8.07 L/100 km.
British cars sold in America
A British compact at 50 mpg UK, 5.65 L/100 km, is 41.6 US mpg, though the EPA label for the same car often reads 35 to 38 mpg because of the harder test. The label is in effect the product of two corrections: one for the gallon and one for the test, both of which lower the American figure.
Fuel cost per mile
At 3.80 dollars per US gallon, 4.56 per imperial gallon, a car doing 32 US mpg or 38.4 UK mpg costs 11.9 cents a mile either way. The cost per mile is the price divided by the mpg in the same gallon. Mixing a US price with a UK mpg gives a cost wrong by 20 per cent.
Hybrids on two scales
A hybrid of 52 US mpg, 4.52 L/100 km, is 62.5 UK mpg. Hybrids rated 60 to 70 UK mpg are therefore the equals of those rated 50 to 58 US. British marketing shows the bigger number, and anyone who compares it with an American rival without converting is misled.
Plug-in hybrids and MPGe
The EPA's MPGe for electric driving uses US gallons, so a car at 100 MPGe is 120 UK-gallon equivalent. A plug-in hybrid of 40 US mpg on petrol is 48 UK mpg. Both numbers are higher on the British scale, and the energy used is unchanged.
Motorcycles
A 600 cc motorcycle at 45 US mpg, 5.23 L/100 km, is 54.0 UK mpg, and a 125 cc scooter at 80 US mpg, 2.94 L/100 km, is 96.1. Magazines in each country use their own unit, so a rider reading both needs the factor to compare them.
More values for convert MPG (US) to MPG (UK)
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 (US) = 3.60285 MPG (UK)
- 7 MPG (US) = 8.40665 MPG (UK)
- 9 MPG (US) = 10.8085 MPG (UK)
- 12 MPG (US) = 14.4114 MPG (UK)
- 15 MPG (US) = 18.0142 MPG (UK)
- 20 MPG (US) = 24.019 MPG (UK)
- 35 MPG (US) = 42.0332 MPG (UK)
- 40 MPG (US) = 48.038 MPG (UK)
Common slips with a “convert MPG (US) to MPG (UK)” calculation
Converting the wrong way
From US to UK the number rises by a fifth. If 30 became 25, you used the factor for the opposite direction, 0.8327.
Assuming "mpg" means one gallon
An advert that just says "mpg" may be American or British. Cars made for North America carry the US gallon and British cars the imperial one. Check where the car is sold.
Thinking a bigger number is a better car
A UK figure is higher for the same car. For an honest comparison, convert both to L/100 km or both to the same mpg first.
Short answers
How do I convert MPG (US) to MPG (UK)?
Multiply the US mpg by 1.2009.
How many UK mpg is 30 US mpg?
36.0 UK mpg.
How many UK mpg is 50 US mpg?
60.0 UK mpg.
How many US mpg is 40 UK mpg?
33.3 US mpg.
Does my number leave my device?
No, the calculation runs in your browser.
More pages and a wrap-up
For other fuel-economy conversions see Convert MPG (US) to L/100km, Convert MPG (US) to km/L, Convert km/L to MPG (UK), Convert L/100km to MPG (UK), Convert MPG (UK) to km/L, Convert km to mi, Convert mi to km, Convert °C to °F, Convert °F to °C. For the opposite direction see Convert MPG (UK) to MPG (US).
In short, a “convert MPG (US) to MPG (UK)” calculation means one multiplication by 1.2009 and a unit written next to the result. Your figure is calculated locally, with no account and no upload.