"700c" is one of the most misread labels in cycling. It is not a measurement in centimetres, it has nothing to do with engine size, and the wheel is not 700 mm across. It is a rim size, and once you know the one number that actually matters, buying tyres or an e-bike conversion wheel becomes simple.
The Quick Answer700c is a rim with a 622 mm bead seat diameter — the diameter where the tyre bead sits. It is the same rim diameter as a "29-inch" mountain-bike wheel and the European "28-inch" wheel; only the tyre widths differ. On any tyre sidewall, look for the ISO (ETRTO) code: xx-622 means it fits a 700c rim, whatever the "c" or inch label says.
What the "700" and the "c" Actually Mean
The name comes from the old French sizing system. "700" was the approximate outside diameter in millimetres of a wheel with its tyre fitted. The letters a, b, c and d were tyre width classes: a was the narrowest and d the widest, and to keep the outside diameter at roughly 700 mm, the wider classes used a smaller rim. Of those, only the "c" rim survived in common use, so "700c" today simply names that rim — not a tyre width and not a centimetre.
That is why the outside diameter of a 700c wheel is not fixed: a 25 mm road tyre and a 45 mm gravel tyre on the same 700c rim give noticeably different overall diameters. The rim itself does not change.
The Number That Matters: 622 mm (ISO / ETRTO)
Because the traditional names are confusing, tyres and rims also carry an ISO 5775 size, usually called the ETRTO size. It has two parts: the tyre width in millimetres and the bead seat diameter in millimetres. A tyre marked 35-622 is 35 mm wide and fits a 622 mm rim — a 700c rim. A tyre marked 700x35c is the same tyre written the French way.
| Common name |
ISO bead seat diameter |
Fits a 700c rim? |
Where you see it |
| 700c |
622 mm |
Yes |
Road, hybrid, gravel, touring bikes |
| 29-inch (29er) |
622 mm |
Same rim diameter |
Mountain bikes, with wider tyres |
| 28-inch (European) |
622 mm |
Same rim diameter |
City and trekking bikes in Europe |
| 27.5-inch / 650b |
584 mm |
No |
Modern mountain and some gravel bikes |
| 27-inch (old) |
630 mm |
No — 8 mm larger |
Older road and touring bikes |
| 26-inch (MTB) |
559 mm |
No |
Older mountain bikes, many fat bikes |
Match the second number of the ISO size. Inch and letter names overlap and can mislead; the bead seat diameter does not.
700c vs 29-Inch: Same Rim, Different Tyres
A 700c wheel and a 29-inch wheel share the 622 mm rim diameter. "29-inch" describes the rough outside diameter once a wide mountain-bike tyre is fitted, while 700c tyres are usually narrower. A 29-inch tyre can go on a 700c rim, and a 700c tyre on a 29er rim, when two conditions are met:
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Rim width suits the tyre width — a narrow road rim will not support a very wide tyre safely, and a wide mountain-bike rim makes a narrow tyre unstable. Check the rim's internal width against the tyre maker's recommended range.
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The frame and fork have clearance — a wider tyre needs room at the chainstays, seatstays, fork crown and brake. Many road frames cannot take mountain-bike widths.
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27-inch is not 700c. Older UK road bikes often use 27-inch (630 mm) rims. They look almost identical, but a 700c tyre will not seat on a 27-inch rim, and a 700c wheel fitted to a 27-inch frame moves the rim 4 mm away from where the brake pads were set.
How to Check Your Wheel Size
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Read the tyre sidewall for the ISO code, such as 32-622 or 40-622. The second number is the rim size.
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Check the rim sticker if the tyre is worn: many rims print their size, for example 622x19 (bead seat diameter x internal width).
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Measure the dropouts: front forks are usually 100 mm; rear frames are usually 130–135 mm for quick-release and 142 mm for thru-axle.
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Note the brake type: rim brakes need a wheel with a braking surface; disc brakes need a rotor mount on the hub.
Our wheel and dropout size guide shows where to measure, and the quick-release vs thru-axle guide covers axle fit.
Choosing a 700c E-Bike Conversion Kit
For a conversion, the motor wheel has to match all of the above: 622 mm rim diameter, the right dropout width, your axle type, your brake type and enough clearance for the tyre you plan to run. Most of our hub kits are offered in 700c as well as 20–29-inch sizes, so the choice is about power and use rather than wheel size.
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Road-legal commuting in the UK — a 250W kit such as the 250W front-wheel kit, with assistance cutting out at 15.5 mph (25 km/h).
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Private-land performance — higher-power rear kits such as the 52V 2000W MTX rim kit, which is outside UK EAPC rules and not for road use.
The 700c conversion kit fit guide goes further into road and gravel frames, and our rim-brake guide explains what to check if your bike has V-brakes or caliper brakes. You can compare sizes across the range in our conversion kits with battery.
FAQs
What does 700c mean on a bike?
It names a rim with a 622 mm bead seat diameter. The "700" is the old nominal outside diameter in millimetres and the "c" is the surviving width class from the French system. It is not 700 mm and not centimetres.
Is 700c the same as 28 inch?
Yes, in the European sense: a 28-inch wheel on a city or trekking bike uses the same 622 mm rim. Check the ISO code on the tyre to be sure, because the old British 27-inch size (630 mm) is different.
Is 700c the same as 29 inch?
Same rim diameter (622 mm), different typical tyre width. A 29-inch tyre fits a 700c rim if the rim width and frame clearance allow it.
Is 700c the same as 27.5 inch?
No. 27.5-inch (650b) rims are 584 mm, so a 700c tyre will not fit a 27.5-inch rim or the other way round.
What tyre widths fit a 700c rim?
It depends on the rim's internal width and your frame clearance, not on the 700c label. Narrow road rims suit roughly 23–32 mm tyres; wider gravel and hybrid rims commonly take 35–50 mm. Follow the tyre and rim makers' compatibility charts.
Can I fit a 700c e-bike conversion kit to my bike?
If your tyres read xx-622, yes in principle. Then check dropout width, axle type, brake type and tyre clearance before ordering the motor wheel.
Sources
About this guide
Author: KirbEbike Editorial. Technical review: KirbEbike conversion-support team. Last reviewed: October 2026. Rim sizes follow ISO 5775 (ETRTO) bead seat diameters; fit advice reflects the motor wheels in our current range.
