Wheel Circumference and Odometer Calibration Calculator
Wheel Circumference and Odometer Calibration Calculator
The nominal rolling circumference from an ISO 5775 tyre marking, the roll-out you actually measured, and what the difference between them costs your odometer over 100 km. The geometry is labelled as geometry, because no standard publishes a circumference.
Nominal circumference, and the error against a measured roll-out
π × (bead seat + 2 × tyre)A 28-622 tyre — a 28 mm section on a 700C bead seat — against a measured roll-out of 2,105 mm
Formula
nominal circumference = π × nominal outside diameter
over-reading per 100 km = (nominal − measured) ÷ measured × 100000
effective rolling radius = measured roll-out ÷ 2π
- ISO 5775 publishes the bead seat, and nothing else
- the standard — developed by the European Tyre and Rim Technical Organisation, now managed by ISO, Part 1 last published August 2023 — marks a clincher tyre with its nominal section width and the nominal rim diameter in millimetres, so “32-597” is a 32 mm section on a 597 mm bead seat. 622 mm is 700C, 584 mm is 650B, 559 mm is a 26-inch mountain bike wheel. NO CIRCUMFERENCE AND NO ROLL-OUT IS PUBLISHED, in the standard or in the tyre-sizing references read for this page
- bead seat + 2 × width is geometry, not a standard
- it assumes the inflated tyre’s height equals its nominal width, which is true of a roughly round-profile tyre and false of a wide tyre on a narrow rim or a narrow one on a wide modern rim, where the measured width can exceed the marking by several millimetres. The page labels the figure nominal everywhere for that reason
- why the measured figure is smaller
- a loaded tyre flattens where it touches the ground, so the circle it rolls is smaller than the free diameter, and more so as pressure falls and the rider gets heavier — which is why a roll-out should be measured with you on the bicycle at the pressure you ride. Sheldon Brown’s own published gain-ratio example used a 340 mm radius for a 700 x 30 tyre where the nominal construction gives 341 mm
- the error is proportional
- an odometer set to a circumference that is 1% too big reads 1% long at every distance, so the error in metres is exactly proportional to the ride. That means the per-100-km figure above scales: multiply by 4 for a 400 km week. It also means the error never averages out
Worked example
A 28-622 tyre — a 28 mm section on a 700C bead seat — against a measured roll-out of 2,105 mm
The nominal outside diameter is 622 + 2 × 28 = 678 mm
The nominal circumference is π × 678 = 2,130.0 mm, which is the figure a tyre-size chart would give you
The measured roll-out is 2,105 mm, so the nominal is 25.0 mm too big — the measurement is 98.826% of it
Set to the nominal figure, the computer over-reads by 1,187.6 m per 100 km: a century ride would come back as 101.19 km
The measurement implies an effective rolling diameter of 670.0 mm and a radius of 335.0 mm, which is the radius to carry to the gearing page
Set the measured roll-out to zero and the comparison rows go blank while the headline stands. Set the bead seat diameter to zero and the panel shows nothing, because there is no wheel
Nominal circumferences from ISO 5775 bead seat diameters
| Wheel | Bead seat | Tyre section | Nominal outside diameter | Nominal circumference | Revolutions per km |
|---|---|---|---|---|---|
| 700C road | 622 mm | 25 mm | 672 mm | 2,111.2 mm | 473.68 |
| 700C road | 622 mm | 28 mm | 678 mm | 2,130.0 mm | 469.48 |
| 700C gravel | 622 mm | 40 mm | 702 mm | 2,205.4 mm | 453.43 |
| 650B, sold as 27.5 inch | 584 mm | 47 mm | 678 mm | 2,130.0 mm | 469.48 |
| 26 inch mountain bike | 559 mm | 50 mm | 659 mm | 2,070.3 mm | 483.02 |
| 27 inch, older road | 630 mm | 25 mm | 680 mm | 2,136.3 mm | 468.10 |
| 20 inch folder | 406 mm | 35 mm | 476 mm | 1,495.4 mm | 668.72 |
What a calibration error costs, in metres
| Measured roll-out | Difference from 2,130.0 mm nominal | As a percentage | Over-reading per 100 km | A 100 km ride reads as |
|---|---|---|---|---|
| 2,130.0 mm | 0.0 mm | 0.000% | 0.0 m | 100.00 km |
| 2,120.0 mm | 10.0 mm too big | 0.469% | 471.7 m | 100.47 km |
| 2,111.0 mm | 19.0 mm too big | 0.892% | 900.0 m | 100.90 km |
| 2,105.0 mm | 25.0 mm too big | 1.174% | 1,187.6 m | 101.19 km |
| 2,090.0 mm | 40.0 mm too big | 1.878% | 1,913.9 m | 101.91 km |
| 2,145.0 mm | 15.0 mm too small | 0.704% | −699.3 m | 99.30 km |
Why nobody publishes a wheel circumference, and what to do instead
This page is about cycling. Two different kinds of number appear in this category and they are not sourced the same way. A regulation — a minimum bicycle weight, a gear rollout limit for a junior rider — is published by a body for a period, and every one quoted here is printed with that body and that edition, because the Union Cycliste Internationale and the national federations revise them. A definition — a gear ratio, a circumference, a rate of climb — belongs to nobody and is the same everywhere, and where this page relies on one it says whose published wording it took it from.
A wheel’s circumference is not a published number and this page does not pretend otherwise. ISO 5775-1, the standard behind the two-number marking on the side of a tyre, publishes the bead seat diameter — 622 mm for a 700C, 584 mm for a 650B, 559 mm for a 26-inch mountain bike wheel — and the nominal section width, and nothing else. Treating the outside diameter as the bead seat diameter plus twice the section width is geometry, not a standard: it assumes the inflated tyre is as tall as it is wide, which a wide tyre on a narrow rim is not, and it assumes no load on it, which is never true. The number your computer needs is the one you measure by rolling the wheel, with you on it.
What the standard does say is more than people expect and less than they want. ISO 5775 — developed by the European Tyre and Rim Technical Organisation, now managed by ISO, Part 1 last published August 2023 — is why a tyre has two numbers on its side. The second is the bead seat diameter in millimetres, where the tyre’s bead sits, and it decides whether a tyre fits at all: 622 mm for 700C and 29 inch, 630 mm for 27 inch, 584 mm for 650B and 27.5 inch, 559 mm for a 26-inch mountain bike wheel. The first is the nominal section width. That is the whole of it — neither ISO 5775 nor the tyre-sizing references read for this page publishes a rolling circumference for anything.
So where does 2,130 mm for a 28-622 come from? From geometry, done openly here rather than presented as a lookup: add twice the section width to the bead seat diameter for an outside diameter, multiply by π. The step doing the work is the first, and it assumes the inflated tyre is as tall as it is wide. That is roughly true of a round-profile tyre on a rim of matched width, false of a wide tyre on a narrow rim, which is taller, and false of a narrow tyre on one of the modern wide rims, where a tyre marked 28 can measure 30 or 31.
And then there is the rider. A loaded tyre flattens where it meets the ground, so the circle the wheel actually rolls is smaller than the free diameter — by more at low pressure, by more under a heavier rider, by more on a soft surface. The direction is always the same: a nominal figure reads too big, so a computer set to one reads too long. Sheldon Brown’s own published gain-ratio example is a small illustration of the same point, using a radius of 340 mm for a 700 x 30 tyre where the nominal construction gives 341 mm.
The number this page cannot look up for you, it asks you for. The calculator engine has no table interpolation of any kind, and a curve fitted to stand in for a published table is worst at its extremes, which is exactly where an answer changes anything. Anyone who needs this calculation already has the figure, printed on the thing this page is about, so that figure is the input and the arithmetic done on it is honest.
The honest answer, then, is to measure it, and it takes two minutes. Pump the tyre to the pressure you actually ride. Stand the bicycle with the valve at the bottom and mark the floor beneath it. Sit on the bicycle — this matters, and is the step most instructions leave out — and have somebody roll you forward until the valve is at the bottom again. Mark the floor and measure between the marks in millimetres. That number is your roll-out, it is what the computer’s circumference setting wants, and the comparison rows above will tell you what you had been losing without it.
Why it is worth doing. The error is strictly proportional, so it never averages out: a circumference 1.17% too big turns a genuine 100 km into 101.19 km and a genuine 1,000 km month into about 1,012 km. It inflates every speed in the same proportion, every segment time comes out fast, and any power figure derived from speed rather than measured at the cranks inherits the error too.
One figure on this page is here for a different purpose. The effective rolling radius row divides your measured roll-out by 2π, which gives the radius the wheel behaves as if it had. That is exactly the input the gear ratio and gain ratio calculator wants for a gain ratio, so a measured roll-out improves the gearing figures as well as the odometer — double it to get a diameter and type that in. For the speed those gears produce at a cadence, the cycling speed from cadence and gearing calculator; and the UCI has a rule about wheel diameter too, which the UCI bike weight and dimension limits interpreter covers: Article 1.3.018 allows between 55 cm and 70 cm including the tyre, so every wheel in the table above except the 20-inch folder is inside it.
Frequently asked questions
How do you calculate a bicycle wheel’s circumference?
Add twice the tyre’s nominal section width to the bead seat diameter, then multiply by π. For a 28-622 tyre that is 622 + 56 = 678 mm, and π × 678 = 2,130 mm. That is a nominal figure derived from geometry, not a published one: ISO 5775 gives the bead seat diameter and the section width and no circumference at all.
How do you measure roll-out properly?
Inflate to your riding pressure, put the valve at the bottom and mark the floor under it, then sit on the bicycle and have somebody roll you forward one full wheel revolution, and mark and measure. Sitting on it is the step that matters: a loaded tyre rolls a smaller circle than an unloaded one, which is the main reason a measured figure beats a calculated one.
Why does my bike computer read long?
Almost always because it was set to a nominal circumference from a tyre chart, which is systematically a little larger than what your loaded wheel actually rolls. The error is proportional, so a figure 1.17% too big turns a genuine 100 km into 101.19 km and never averages out. A measured roll-out fixes it.
What is the bead seat diameter and why does it matter more than the inch size?
It is the diameter of the rim where the tyre’s bead sits, in millimetres, and it is the second number in an ISO 5775 marking. It matters because inch labels are unreliable: “26 inch” covers 559 mm, 571 mm and 584 mm wheels, and 584 mm tyres are sold as 27.5 inch. If the ISO number matches the rim, the tyre fits; if it does not, it will not.
Do a 650B and a 700C wheel give the same gearing?
They can, and that is why gravel bicycles swap between them. A 47 mm tyre on a 584 mm bead seat and a 28 mm tyre on a 622 mm one both come to a nominal 678 mm outside diameter, so the nominal circumference, the development and the gear inches are identical. Measure both, though: nominal section widths are the least reliable part of the calculation.
Related calculators
References
- Wikipedia. ISO 5775 (read 15 Oct 2026; about 9,000 to 10,000 characters, designation table as readable TEXT). ISO 5775 was developed by the European Tyre and Rim Technical Organisation and is now managed by ISO; Part 1, “Bicycle tyres and rims: Part 1: Tyre designations and dimensions”, was last published August 2023 and Part 2, “Part 2: Rims”, March 2021. A clincher tyre carries its nominal section width and the nominal rim diameter in millimetres separated by a hyphen, so “32-597” is a 32 mm section on a 597 mm bead seat. Bead seat diameters: 622 mm (700C), 584 mm (650B, sold as 27.5 inch), 559 mm (26 inch mountain bike), 507 mm (24 inch), 406 mm (20 inch). The page warns that inch labels do not reliably indicate a bead seat diameter and that its own citations are to the superseded 1997 and 1996 editions, so a specific row should be checked against the standard.
- Sheldon Brown. “Tire Sizing Systems”, sheldonbrown.com/tire-sizing.html (read 15 Oct 2026; about 25,000 characters, tables as readable text). An independent corroboration of the bead seat diameters: 622 mm for 700C, 584 mm for 650B, 559 mm for 26-inch tyres from 26 x 1.00 to 5.0, 630 mm for 27 inch, with the warning that “26 inch” also covers 571 mm and 584 mm wheels. On the two-number system the bead seat diameter is “the critical one”: “Generally, if this number matches, the tire will fit onto the rim; if it doesn’t match, the tire won’t fit”. IMPORTANT, and the reason the odometer page is built as it is: this page gives NO formula for rolling circumference or roll-out from a tyre size and says nothing about why a measured roll-out differs from a calculated one. Neither does ISO 5775. No published circumference table is quoted anywhere in this batch.
- Sheldon Brown. “Gain Ratios”, sheldonbrown.com/gain.html (read 15 Oct 2026; about 9,000 characters of which the article and its radius-ratio table are 5,000 to 6,000, and the table came through as readable TEXT). The source for gain ratio here. Two steps: “Find the radius ratio by dividing wheel radius by crank length”, done once per bicycle, then multiply by front teeth over rear. Of the answer: “This number is a pure ratio, the units cancel out”, so for each unit the pedal travels in its orbit the bicycle travels that many. BOTH published worked examples are reproduced through this site’s engine: a 700 x 30 road bike, 340 mm wheel radius, 170 mm cranks, radius ratio 2.0, 53/19 giving 5.58; and a mountain bike, 13 in radius, 6¾ in cranks, 46/16 giving 5.54. On the alternatives: “the handwriting is on the wall for all inch-based measurement systems”, and metres of development is “a bit more cumbersome” for needing a multiplication by π, “an irrational one, no less”.
- Union Cycliste Internationale. Clarification Guide of the UCI Technical Regulation, cover “01.01.2023 version”, the English copy hosted by Pyöräilyliitto, the Finnish cycling federation (read 15 Oct 2026; about 100,000 characters, reaching the middle of the guide inside Art. 1.3.024 and ending mid-sentence). The English wording two years on, and all six figures UNCHANGED from the 2021 French edition: “The weight of the bicycle cannot be less than 6.8 kilograms” (1.3.019); “A bicycle shall not measure more that 185 cm in length and 50 cm in width overall” (1.3.012, the typo as printed); “The peak tip of the saddle shall be a minimum of 50 mm to the rear of a vertical plane” through the bottom bracket spindle, with an exemption allowing the peak forward “until the vertical line passing through the bottom bracket spindle” (1.3.013); “between 54 cm minimum and 65 cm maximum” and “between 35 cm minimum and maximum 50 cm” (1.3.016); “Wheels of the bicycle may vary in diameter between 70 cm maximum and 55 cm minimum, including the tyre” (1.3.018); “The length of the saddle shall be 24 cm minimum and 30 cm maximum” with “A tolerance of 5mm is allowed” (1.3.014). NOT USED FROM THIS FETCH: the time-trial handlebar figures of Art. 1.3.023, because the text returned overlapping old and new values in the same cells (“4cm 50 mm”) and the authorised-positions chart came through scrambled. Diagrams are images and appear only as captions.