Bike Wheel Size and Circumference Calculator

Wheel diameter, circumference, and the number to type into your bike computer.

Or enter it yourself

mm
622 for 700c and 29in, 584 for 27.5, 559 for 26in.
mm
Both numbers are on your tyre as 622-28.
How much the tyre flattens under you. ~0.5% road, ~1.5% MTB, ~2.5% fat.

Set your bike computer to

—mm

Overall diameter
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Circumference
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Turns per km
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mm
Rim and tyre drawn to scale from your two numbers.
Measure it exactly with a roll-out

The accurate way, and the one every computer manual recommends. Pump the tyre to your normal pressure, mark the tyre and the floor at the valve, sit on the bike and roll forward in a straight line, then measure between the marks. Two or three turns average out the error.

m

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What number a bike computer actually wants

It wants the rolling circumference in millimetres — how far the wheel travels in one full turn with you on the bike. Not the diameter, not inches.

That is slightly less than π × diameter, because the tyre flattens where it touches the ground. Half a percent on a hard road tyre, two or three on a soft fat tyre. Whatever you set it to, your speed and distance are wrong by the same percentage — so a 20 mm error is about 1% on every ride.

Get it close with the calculator, or exactly right with a roll-out.

Wheel size chart

Tyre ISO Diameter Circumference Computer
700c × 23 622-23 668 mm 2099 mm 2086 mm
700c × 25 622-25 672 mm 2111 mm 2098 mm
700c × 28 622-28 678 mm 2130 mm 2117 mm
700c × 32 622-32 686 mm 2155 mm 2142 mm
700c × 38 622-38 698 mm 2193 mm 2180 mm
700c × 42 622-42 706 mm 2218 mm 2205 mm
29 × 2.1 622-53 728 mm 2287 mm 2273 mm
29 × 2.4 622-61 744 mm 2337 mm 2323 mm
27.5 × 2.25 584-57 698 mm 2193 mm 2180 mm
27.5 × 2.4 584-61 706 mm 2218 mm 2205 mm
650b × 47 584-47 678 mm 2130 mm 2117 mm
27in × 1¼ 630-32 694 mm 2180 mm 2167 mm
26 × 1.95 559-50 659 mm 2070 mm 2058 mm
26 × 2.125 559-54 667 mm 2095 mm 2083 mm
26 × 4.0 fat 559-102 763 mm 2397 mm 2383 mm
24 × 1.75 507-44 595 mm 1869 mm 1858 mm
20 × 1.75 406-44 494 mm 1552 mm 1543 mm
20 × 1⅛ 451-28 507 mm 1593 mm 1583 mm
16 × 1.75 305-44 393 mm 1235 mm 1227 mm

Computer column assumes 0.6% squash. Your manual may list a figure a few millimetres either side — those tables are old and averaged, and a roll-out beats both.

Reading the size off your tyre

Look for two numbers with a dash, like 622-28 or 28-622. That is the ISO size: tyre width and rim bead seat diameter, both in millimetres. It is the only marking that is never ambiguous, and it is the one to use here.

The inch and French names are nicknames. “26 inch” has meant at least four different rim diameters over the years, and 700c, 29er and 28 inch are all the same 622 mm rim. If the two sets disagree, trust the ISO number.

Which wheel size for your height

Wheel size is mostly set by the bike, not by you — almost every adult bike now uses 622 mm rims whatever your height. Frame size is what you fit to your body.

The one place height still matters is mountain bikes. Riders under about 165 cm often prefer 27.5in for standover and handling; taller riders generally get on better with 29in. Many brands now mix the two on the same bike.

FAQs

What wheel size do I enter for 700 × 28c?

About 2121 mm. A 622 mm rim with a 28 mm tyre is 678 mm across and 2130 mm round, less roughly half a percent for tyre squash.

How do I measure wheel circumference myself?

Mark the tyre and the floor at the valve, sit on the bike, roll forward one full turn in a straight line and measure between the marks. That distance in millimetres is the number. The helper in the calculator does the sum.

Is 29er the same as 700c?

Yes, the same 622 mm rim. The tyres are much wider, so the wheel ends up bigger overall and the circumference is different — which is why you cannot reuse a road bike's computer setting on a mountain bike.

Why is my computer reading the wrong distance?

Almost always the wheel size. Put what is currently in your computer into the box above and it will tell you how far out it is. A worn tyre, a wider replacement or lower pressure will all shift it slightly too.

Does tyre pressure change the setting?

A little. Lower pressure squashes the tyre more and shortens the rolling circumference — worth up to about 1% between a hard and a soft tyre. Worth redoing the roll-out if you change pressure a lot.