Bicycle Tire Sizes: ISO Chart, Widths and What Fits Your Rim
Bicycle tires carry two or three different size labels, and several sizes share the same nominal name. The one number that decides fit is the ISO bead seat diameter. This chart maps every common name to it.
A bicycle tire fits a rim only if its ISO bead seat diameter matches: 622 mm for 700c and 29er, 584 mm for 27.5 in (650b), and 559 mm for 26 in mountain bikes. A tire marked 28-622 is the same as 700x28c: 28 mm wide on a 622 mm rim, about 26.7 in (678 mm) in outside diameter.
- 700c / 29er
- 622 mm bead seat
- 27.5 in / 650b
- 584 mm bead seat
- 26 in MTB
- 559 mm bead seat
- 20 in BMX
- 406 mm bead seat
On this page
Bicycle tire size chart (ISO / ETRTO)
The ISO 5775 system (also called ETRTO) gives every tire two numbers: the width in millimeters and the bead seat diameter (BSD) of the rim, also in millimeters. A tire marked 57-559 is 57 mm wide and fits a 559 mm rim. Every traditional name maps to one BSD:
| Common name | ISO bead seat | Typical widths | Used on |
|---|---|---|---|
| 700c, 29 in, 28 in | 622 mm | 23-50 mm; 2.1-2.6 in | Road, gravel, hybrid, 29er MTB, most adult city bikes |
| 28 x 1 1/2 (F10) | 635 mm | 37-40 mm | Traditional Dutch and roadster bikes |
| 27 in (27 x 1 1/4) | 630 mm | 28-32 mm | Road bikes from before about 1990 |
| 650b, 27.5 in | 584 mm | 40-50 mm; 2.2-2.8 in | Mountain bikes, gravel and randonneur bikes |
| 650c | 571 mm | 20-23 mm | Small road and triathlon bikes |
| 26 x 1 3/8 (EA3) | 590 mm | 35-37 mm | Older British-style 3-speed bikes |
| 26 in (decimal widths) | 559 mm | 1.5-2.6 in; fat 3.8-5 in | Older mountain bikes, cruisers, fat bikes, touring |
| 24 in (decimal widths) | 507 mm | 1.75-2.4 in | Kids' mountain bikes, small adults |
| 20 in (decimal widths) | 406 mm | 1.5-2.4 in | BMX, kids' bikes, folding bikes |
| 20 x 1 1/8 or 1 3/8 | 451 mm | 28-37 mm | Some folding bikes and recumbents |
| 16 in | 305 mm | 1.75-2.125 in | Kids' bikes, some folding bikes |
| 16 x 1 3/8 | 349 mm | 35 mm | Brompton and similar folding bikes |
| 14 in | 254 mm | 2.125 in | Kids' bikes |
| 12 in (12 1/2 x 2 1/4) | 203 mm | 2.125-2.4 in | Kids' and balance bikes |
"26 inch" can mean 559, 571 or 590 mm, and "28 inch" can mean 622 or 635 mm. Tires that differ by even a few millimeters of BSD will not seat. A rule of thumb: inch sizes with a decimal width (26 x 2.10) and with a fraction width (26 x 1 3/8) are not interchangeable. Read the ISO number on the old tire's sidewall.
How big is a bicycle wheel? Outside diameters
Outside diameter is roughly the bead seat plus twice the tire width. This matters for frame clearance, bike racks and fitting a wheel into a car or bag.
| Tire | ISO size | Outside diameter |
|---|---|---|
| 700x25c (road) | 25-622 | 26.5 in (672 mm) |
| 700x28c (road) | 28-622 | 26.7 in (678 mm) |
| 700x32c (endurance road, hybrid) | 32-622 | 27.0 in (686 mm) |
| 700x40c (gravel) | 40-622 | 27.6 in (702 mm) |
| 29 x 2.4 (MTB) | 61-622 | 29.3 in (744 mm) |
| 27.5 x 2.4 (MTB) | 61-584 | 27.8 in (706 mm) |
| 27.5 x 2.8 (plus) | 71-584 | 28.6 in (726 mm) |
| 26 x 2.1 (MTB) | 53-559 | 26.2 in (666 mm) |
| 26 x 4.0 (fat bike) | 102-559 | 30.0 in (762 mm) |
| 20 x 1.95 (BMX) | 50-406 | 19.9 in (505 mm) |
Note how close a 27.5 x 2.8 plus tire (28.6 in) is to a 29er. Many frames designed for 29 x 2.4 also accept 27.5 x 2.8, which is the basis of "plus" conversions.
Tire width by type of bike
Road widths are labeled in millimeters, mountain-bike widths in inches. To convert inches to millimeters, multiply by 25.4: 2.2 in = 56 mm, 2.4 in = 61 mm, 2.6 in = 66 mm.
| Bike type | Typical width | Rim inner width (common pairing) |
|---|---|---|
| Road racing | 25-30 mm | 19-23 mm |
| Endurance road, all-road | 30-35 mm | 21-25 mm |
| Gravel | 38-50 mm | 23-27 mm |
| Hybrid, city, commuter | 32-47 mm | 17-23 mm |
| Cross-country MTB | 2.2-2.4 in (56-61 mm) | 25-30 mm |
| Trail and enduro MTB | 2.3-2.6 in (58-66 mm) | 29-35 mm |
| Plus MTB | 2.8-3.0 in (71-76 mm) | 35-45 mm |
| Fat bike | 3.8-5.0 in (97-127 mm) | 65-100 mm |
| BMX | 1.95-2.4 in (50-61 mm) | Varies |
Road tires have grown wider over the past decade because wider tires at lower pressure roll as fast on real roads and grip better. Older rim-brake road frames often clear only 25-28 mm; disc-brake road frames commonly clear 32-35 mm.
A tire's real width depends on the rim. On a wider rim it measures wider, roughly 1 mm more for each 2-3 mm of extra inner rim width. A 28 mm road tire can measure 30 mm on a modern 23 mm inner-width rim, which matters for frame clearance.
Reading all the markings on a bike tire
- ISO / ETRTO:
28-622. The definitive fit size. - French:
700x28c. The letter (a, b, c) originally described tire widths on different rims; only 700c and 650b/650c remain in use. - Inch:
29 x 2.40or28 x 1 5/8 x 1 3/8. Approximate outside diameter and width. - Pressure range: printed in psi and bar, for example 50-80 psi (3.5-5.5 bar). Never exceed the maximum, or the rim's maximum if lower.
- TLR / TR / Tubeless Ready: designed to run sealant without a tube on a tubeless rim.
- Rotation arrow: fit with the arrow pointing forward at the top of the wheel.
Hookless rims have straight inner walls and no bead hook. The ETRTO and ISO rules limit them to 5 bar (73 psi) and require tubeless-compatible tires approved for hookless use. Check the tire maker's hookless compatibility list before fitting a narrow road tire.
Inner tubes and valves
Tubes are sold for a BSD and a width range, for example 700 x 25-32c or 29 x 2.1-2.5. Any tube labeled for your BSD and a range that includes your tire width will fit.
- Presta (French) valve: slim, needs a 6.5 mm rim hole. Standard on road and most performance bikes. Valve lengths run 32-80 mm; deep rims (40 mm or more) need 60 mm or longer.
- Schrader (car) valve: needs an 8.5 mm hole. Common on kids' bikes, BMX and budget bikes. A gas-station pump fits it.
- Dunlop (Woods) valve: uses the Schrader-size hole but inflates with a Presta pump head. Common on European city bikes.
Kids' bike wheel sizes by age
Children's bikes are sized by wheel diameter. These ranges are typical; brands vary, and leg length (inseam) is the better guide.
| Wheel size | Typical age | Inseam | ISO bead seat |
|---|---|---|---|
| 12 in | 2-4 years | 14-17 in (36-43 cm) | 203 mm |
| 14 in | 3-5 years | 16-20 in (41-51 cm) | 254 mm |
| 16 in | 4-6 years | 18-22 in (46-56 cm) | 305 mm |
| 20 in | 6-9 years | 20-25 in (51-64 cm) | 406 mm |
| 24 in | 8-11 years | 24-28 in (61-71 cm) | 507 mm |
| 26 in / 27.5 in | 11+ years | 26 in+ (66 cm+) | 559 / 584 mm |
Frame size for adults is a separate measurement covered in the bicycle size guide, with sport-specific frames in the bike sizing chart. For motorized two-wheelers, see the motorcycle tire size guide; car tire codes are decoded in the tire size chart.
Frequently asked questions
Is 700c the same as 29 inch?
Yes, for fit. Both use a 622 mm bead seat diameter, so any 700c tire fits a 29er rim and vice versa, as long as the width suits the rim and frame. The names differ because 29er tires are wide mountain-bike tires that measure about 29 in across, while a 700x25c road tire is about 26.5 in.
Will a 27-inch tire fit a 700c rim?
No. A 27 in (27 x 1 1/4) tire has a 630 mm bead seat, 8 mm larger than 700c (622 mm). It will not seat on a 700c rim, and a 700c tire is too small for a 27 in rim. Older road bikes often need a brake adjustment to switch.
What does 26 x 2.125 mean?
It means a nominal 26 in diameter and a width of 2.125 in (54 mm). Inch sizes written with a decimal width use the 559 mm mountain-bike rim. Sizes written with a fraction (26 x 1 3/8) use different rims, so always check the ISO number.
What size bike tire for a child?
Typical wheel sizes are 12 in for ages 2-4, 14 in for ages 3-5, 16 in for ages 4-6, 20 in for ages 6-9 and 24 in for ages 8-11. Inseam matters more than age: the child should reach the ground with the balls of both feet when seated.
Can I put wider tires on my bike?
Usually one size up works if the frame and fork leave at least 4-6 mm of clearance on each side and above the tire. Rim brakes limit width most; disc-brake road bikes often take 32-35 mm and gravel bikes 45-50 mm. The rim's inner width must also suit the tire.
Are Presta and Schrader inner tubes interchangeable?
Only in one direction without changes. A Presta tube fits a Schrader rim with an adapter or grommet, but a Schrader valve needs a rim hole of about 8.5 mm versus 6.5 mm for Presta, so it will not fit a Presta-drilled rim unless the hole is enlarged.