MPG to Litres per 100km: Formula and Conversion Table

To convert UK mpg to litres per 100km, divide 282.480936 by the mpg figure. For example, 45 mpg is 282.480936 / 45 = 6.28 litres per 100km. The same formula works in reverse: divide 282.480936 by the L/100km figure to get UK mpg. For km per litre, divide 100 by L/100km.

What is the formula for converting mpg to L/100km?

L/100km = 282.480936 / UK mpg. The number comes from two exact conversion constants: one UK gallon is 4.54609 litres and one mile is 1.609344 km. Multiply 4.54609 by 100, then divide by 1.609344, and you get 282.480936.

You can check it by hand. A car doing 1 mpg travels 1.609344 km on 4.54609 litres. To cover 100 km it would need 100 / 1.609344 x 4.54609 = 282.48 litres. At 45 mpg, it needs one forty-fifth of that: 6.28 litres.

This formula is for UK (imperial) mpg. American mpg uses a smaller gallon. If your figure is from a US source, convert it to UK mpg first, or use 235.214583 / US mpg. Our guide to UK vs US mpg explains the difference.

How do you convert litres per 100km to mpg?

UK mpg = 282.480936 / L/100km. The formula is the same in both directions, because the two measures are inversely related. A car using 6.0 litres per 100km does 282.480936 / 6.0 = 47.1 mpg.

Worked example: a van uses 9.0 litres per 100km. 282.480936 / 9.0 = 31.4 mpg.

What is the conversion table for mpg to L/100km?

The table gives UK mpg alongside litres per 100km, km per litre and US mpg. Figures are rounded to one decimal place.

UK mpg	Litres per 100km	km per litre	US mpg
20	14.1	7.1	16.7
25	11.3	8.9	20.8
30	9.4	10.6	25.0
35	8.1	12.4	29.1
40	7.1	14.2	33.3
45	6.3	15.9	37.5
50	5.6	17.7	41.6
55	5.1	19.5	45.8
60	4.7	21.2	50.0
65	4.3	23.0	54.1
70	4.0	24.8	58.3

And the other way, from litres per 100km to UK mpg:

Litres per 100km	UK mpg	km per litre
4	70.6	25.0
5	56.5	20.0
6	47.1	16.7
7	40.4	14.3
8	35.3	12.5
9	31.4	11.1
10	28.2	10.0
12	23.5	8.3

How do you convert mpg to km per litre?

Multiply UK mpg by 0.354006. That is 1.609344 divided by 4.54609. So 45 mpg is 45 x 0.354006 = 15.9 km per litre. From L/100km, divide 100 by the figure: 6.28 L/100km is 100 / 6.28 = 15.9 km per litre.

Km per litre is used in some countries and in some fleet systems. It reads in the same direction as mpg: higher is better.

Why does a small mpg gain look different in L/100km?

Because the two scales are not linear against each other. L/100km measures fuel used per distance, and mpg measures distance per fuel. The same fuel saving looks bigger at low mpg than at high mpg.

Take a vehicle going from 20 to 25 mpg. L/100km drops from 14.1 to 11.3, a saving of 2.8 litres every 100km. A vehicle going from 40 to 45 mpg, also a gain of 5 mpg, drops from 7.1 to 6.3, a saving of only 0.8 litres every 100km. Same five mpg, more than three times the fuel difference.

For fleets this matters when you prioritise. Fixing a thirsty 20 mpg vehicle often saves more fuel than improving an efficient one by the same number of mpg. Litres per 100km makes that plain, which is why it is the better scale for comparing fuel use.

Which unit should a fleet use?

Use whichever your drivers and your systems already work in, but keep one unit for the whole fleet. In the UK, vehicle adverts and the pump price in pounds per litre mix mpg with litres. The cost sum needs litres per mile or per km, so converting once and sticking to it avoids mistakes.

To go from mpg to money, see how to calculate fuel cost for a journey. To measure your own mpg properly first, use how to calculate mpg. The fuel cost calculator also converts between mpg, L/100km, km per litre and US mpg in one place.

Frequently Asked Questions

How do I convert mpg to litres per 100km?

Divide 282.480936 by your UK mpg. At 45 mpg the result is 6.28 litres per 100km. The constant is 4.54609 litres per UK gallon multiplied by 100 and divided by 1.609344 km per mile.

How do I convert litres per 100km to mpg?

Divide 282.480936 by the L/100km figure. A vehicle using 8 litres per 100km does 282.480936 / 8 = 35.3 UK mpg. The formula is the same in both directions.

How many km per litre is 40 mpg?

40 mpg is 14.2 km per litre. Multiply UK mpg by 0.354006, or divide 100 by the L/100km figure, which is 7.06 at 40 mpg.

Is 50 mpg good in litres per 100km?

50 UK mpg is 5.65 litres per 100km. Compare it against your own measured figure rather than the brochure, because official figures come from a lab test.

Does this formula work for US mpg?

Not directly. US mpg uses a US gallon of 3.785411784 litres, so the constant is 235.214583 instead of 282.480936. Or convert US mpg to UK mpg by dividing by 0.832674, then use the formula above.

Cut your fleet’s fuel bill

Find your own number with the fuel cost calculator. Enter your vehicle’s mpg or L/100km and it shows the cost per mile and the annual bill using this week’s DESNZ prices, as well as converting between units.

A speed cap saves fuel on every journey without the driver having to remember it. The Department for Transport’s fuel consumption curves (TAG data book v2.03, May 2026) show a diesel van using 14.5% less fuel per mile at 60 mph than at 68 mph. How much of that reaches your bill depends on how many of your miles are driven above the cap. See fuel savings from speed limiters.

Talk to us. AutoKontrol has made speed limiters in Britain since 1985, with nationwide installation where we come to you. Book a free consultation or get a quote.