Miles per US gallon to US gallons per 100 miles

Type a value in Miles per US gallon and get the result in US gallons per 100 miles, calculated exactly.

gal/100 mi (US) = 100 ÷ mpg (US) Fuel economy converter

From

Precision

Exact factorRounded for display to about 10 significant digits.

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Formula

gal/100 mi (US) = 100 ÷ mpg (US)

Miles per US gallon and US gallons per 100 miles are inversely related: divide 100 by the value in Miles per US gallon to get US gallons per 100 miles.

Worked examples

1 mpg (US) = 100 gal/100 mi (US)
30 mpg (US) ≈ 3.333333333 gal/100 mi (US)
100 mpg (US) = 1 gal/100 mi (US)

This factor is exact by definition.

Conversion table

Miles per US gallon to US gallons per 100 miles
Miles per US gallon (mpg (US))	US gallons per 100 miles (gal/100 mi (US))
10	10
15	≈ 6.666667
20	5
25	4
30	≈ 3.333333
35	≈ 2.857143
40	2.5
45	≈ 2.222222
50	2
60	≈ 1.666667
70	≈ 1.428571

Values marked ≈ are rounded; the rest are exact.

Reverse table: US gallons per 100 miles to Miles per US gallon

US gallons per 100 miles to Miles per US gallon
US gallons per 100 miles (gal/100 mi (US))	Miles per US gallon (mpg (US))
10	10
15	≈ 6.666667
20	5
25	4
30	≈ 3.333333
35	≈ 2.857143
40	2.5
45	≈ 2.222222
50	2
60	≈ 1.666667
70	≈ 1.428571

Unit definitions

Miles per US gallon mpg (US): Miles travelled per US gallon: about 0.425144 km/L.
US gallons per 100 miles gal/100 mi (US): US gallons used to travel 100 miles, as shown on US fuel economy labels.

Questions people ask

Miles per US gallon to US gallons per 100 miles: what is the conversion factor?

One mpg (US) is 100 gal/100 mi (US).

How do I convert Miles per US gallon to US gallons per 100 miles?

Use the formula above. For example, 30 mpg (US) = ≈ 3.333333333 gal/100 mi (US).

Is the conversion exact?

Yes. Both units have exact definitions, so the factor is exact; a result is only rounded when its decimals never end.

Factors checked 19 October 2026.