Bike wheel circumference from ETRTO tire size

Every bicycle tire carries a marking of two numbers, such as 28-622, defined by the standard ISO 5775 and still often called the ETRTO size. The first number is the width of the tire in millimeters. The second is the bead seat diameter of the rim it fits, also in millimeters. Unlike names such as twenty-six inch or seven hundred C, the marking is unambiguous.

The standard says the overall diameter of a tire is the rim diameter plus twice the height of the tire, and for most tires the height is about the same as the width. So wheel diameter = bead seat diameter + 2 × tire width, and circumference = π × diameter. Sheldon Brown's guide to calibrating bike computers gives the same sum.

It is an estimate. Tire makers do not all measure width the same way, a tire sits wider or narrower depending on the rim, and tread adds height. The same guide puts chart or formula values within one or two percent of the truth, and notes that a road tire carrying a rider rolls about one percent shorter than its unloaded size. That is the allowance the calculator lets you take off.

Published charts do not settle it either. Two computer makers' charts opened on the same day give figures more than twenty millimeters apart for the same common road tire, and one of them calls its own values advisory. Some chart rows equal the formula to the millimeter; others were measured on a particular tire.

For a setting you can rely on, both makers describe a roll-out test: mark the floor at the valve, roll the bike forward one full wheel turn and measure between the marks. One of them asks for the rider on the bike and the tires at riding pressure; the other takes a few millimeters off for the rider's weight.

Bike tire circumference chart: by tire width and rim size

Each cell is the wheel circumference from the formula for the tire width in millimeters in its row and the rim in its column, with no allowance for load.

	Rim size
20 mm	2,080 mm	1,960 mm	1,882 mm	1,401 mm
23 mm	2,099 mm	1,979 mm	1,901 mm	1,420 mm
25 mm	2,111 mm	1,992 mm	1,913 mm	1,433 mm
28 mm	2,130 mm	2,011 mm	1,932 mm	1,451 mm
30 mm	2,143 mm	2,023 mm	1,945 mm	1,464 mm
32 mm	2,155 mm	2,036 mm	1,957 mm	1,477 mm
35 mm	2,174 mm	2,055 mm	1,976 mm	1,495 mm
38 mm	2,193 mm	2,073 mm	1,995 mm	1,514 mm
40 mm	2,205 mm	2,086 mm	2,007 mm	1,527 mm
45 mm	2,237 mm	2,117 mm	2,039 mm	1,558 mm
50 mm	2,268 mm	2,149 mm	2,070 mm	1,590 mm
55 mm	2,300 mm	2,180 mm	2,102 mm	1,621 mm
60 mm	2,331 mm	2,212 mm	2,133 mm	1,652 mm
65 mm	2,362 mm	2,243 mm	2,165 mm	1,684 mm

Rim size

Tire width

622 = 700C, 29 inch

584 = 650B, 27.5 inch

559 = 26 inch mountain bike

406 = 20 inch, BMX and folding

20 mm

2,080 mm

1,960 mm

1,882 mm

1,401 mm

23 mm

2,099 mm

1,979 mm

1,901 mm

1,420 mm

25 mm

2,111 mm

1,992 mm

1,913 mm

1,433 mm

28 mm

2,130 mm

2,011 mm

1,932 mm

1,451 mm

30 mm

2,143 mm

2,023 mm

1,945 mm

1,464 mm

32 mm

2,155 mm

2,036 mm

1,957 mm

1,477 mm

35 mm

2,174 mm

2,055 mm

1,976 mm

1,495 mm

38 mm

2,193 mm

2,073 mm

1,995 mm

1,514 mm

40 mm

2,205 mm

2,086 mm

2,007 mm

1,527 mm

45 mm

2,237 mm

2,117 mm

2,039 mm

1,558 mm

50 mm

2,268 mm

2,149 mm

2,070 mm

1,590 mm

55 mm

2,300 mm

2,180 mm

2,102 mm

1,621 mm

60 mm

2,331 mm

2,212 mm

2,133 mm

1,652 mm

65 mm

2,362 mm

2,243 mm

2,165 mm

1,684 mm

Work out your own numbers: Bike wheel circumference calculator

Chart: wheel circumference on a road rim, by tire width and load allowance

Each cell is the circumference for the tire width in millimeters in its row with the allowance in its column taken off. Rim = 622 mm (700C).

	Allowance for the loaded tire
23 mm	2,099 mm	2,078 mm	2,057 mm
25 mm	2,111 mm	2,090 mm	2,069 mm
28 mm	2,130 mm	2,109 mm	2,087 mm
30 mm	2,143 mm	2,121 mm	2,100 mm
32 mm	2,155 mm	2,134 mm	2,112 mm
35 mm	2,174 mm	2,152 mm	2,131 mm
40 mm	2,205 mm	2,183 mm	2,161 mm
45 mm	2,237 mm	2,214 mm	2,192 mm

Allowance for the loaded tire

Tire width

0 %

1 %

2 %

23 mm

2,099 mm

2,078 mm

2,057 mm

25 mm

2,111 mm

2,090 mm

2,069 mm

28 mm

2,130 mm

2,109 mm

2,087 mm

30 mm

2,143 mm

2,121 mm

2,100 mm

32 mm

2,155 mm

2,134 mm

2,112 mm

35 mm

2,174 mm

2,152 mm

2,131 mm

40 mm

2,205 mm

2,183 mm

2,161 mm

45 mm

2,237 mm

2,214 mm

2,192 mm

Work out your own numbers: Bike wheel circumference calculator

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Bike wheel circumference calculatorWheel circumference and diameter from the size printed on the tire.

Wheel circumference from the tire size

Bike tire circumference chart: by tire width and rim size

Chart: wheel circumference on a road rim, by tire width and load allowance

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