Quick answer
Bike wheels are named in several overlapping systems, so one wheel can carry two or three different labels. The most reliable number is the bead seat diameter in millimeters (the ISO or ETRTO figure; see converting between inch, metric and ETRTO tire sizes), because it describes the rim the tire actually sits on. The chart below connects the common names to that number.
Bike wheel size chart
| Common name | ISO / ETRTO rim diameter | Typically found on |
|---|---|---|
| 12 inch | 203 mm | Small kids’ bikes |
| 14 inch | 254 mm | Kids’ bikes |
| 16 inch | 305 mm | Kids’ bikes |
| 18 inch | 355 mm | Kids’ bikes |
| 20 inch (BMX/kids) | 406 mm | Kids’ bikes, BMX, many folding bikes |
| 24 inch | 507 mm | Larger kids’ and youth bikes |
| 26 inch (mountain) | 559 mm | Older mountain bikes, dirt jump, some youth bikes |
| 27.5 inch / 650b | 584 mm | Mountain bikes, some gravel and touring bikes |
| 700c / 28 inch / 29 inch | 622 mm | Road, hybrid, gravel, city and 29er mountain bikes |
Treat the table as a starting point. A few older or regional sizes share the same inch label but use a different rim, so confirm what is printed on your tire (see how to measure your bike wheel size).
Why one wheel has several names
- Inch names such as 26 or 29 describe a rough overall diameter, and they were never standardized tightly. Two wheels both called “26 inch” can have different rims.
- French names such as 700c and 650b come from older road and touring systems (more in what 700c really means and 650b tires). They are still common on road, gravel and city bikes.
- ISO/ETRTO is the modern standard. A marking like 40-622 means a 40 mm wide tire on a 622 mm rim.
That is why a 29-inch mountain bike wheel and a 700c road wheel use the same 622 mm rim, even though the tires are very different widths.
Wheel size is not frame size
Riders often mix the two up. Wheel size is the diameter of the wheel. Frame size is a separate measurement, usually a number in centimeters or a letter size such as S, M or L. On kids’ bikes the wheel size largely defines the bike, so it works well as the main sizing number. On adult bikes the frame size matters more for fit, and the wheel size follows from the type of bike. See bike wheel sizes by rider height for how this plays out.
Which wheel size suits which bike
- Road, gravel, hybrid and city bikes mostly use 622 mm (700c) wheels, with 584 mm (650b) appearing on some gravel, touring and smaller frames.
- Mountain bikes today are mostly 29-inch or 27.5-inch, with 26-inch found on older bikes and some specialist ones. Our mountain bike wheel sizing guide compares them.
- Kids’ bikes run from 12 inch up to 24 inch or more. The kids bike wheel size by age article has an age and height guide.
- 26-inch bikes still turn up on used bikes and youth models; see who a 26-inch wheel bike is for.
Approximate guide by rider
These ranges are rough and vary by brand and bike type, so use them only as a starting point.
| Rider | Wheel size often considered |
|---|---|
| Toddlers and young children | 12 to 16 inch |
| Children roughly 5 to 9 years old | 20 inch |
| Pre-teens | 24 inch |
| Teens and shorter adults | 26 inch or 27.5 inch |
| Most adults | 27.5 inch, 29 inch or 700c depending on the bike |
Can you swap wheel sizes?
Usually not casually. The frame, fork and brakes are designed around one wheel diameter. A different size can change brake alignment, tire clearance and handling. Some bikes accept two sizes (for example 27.5 or 29 inch) but only when the manufacturer lists it. Check the frame’s documentation or ask a shop before swapping.
FAQ
What size bike should I get based on my height?
For adults, choose the frame size from height and inseam first, using the maker’s chart. The wheel size then comes with the type of bike. See bike wheel sizes by rider height.
Is a 26 inch bike for adults?
It can be. Many shorter adults ride 26-inch bikes comfortably, though most newer adult mountain bikes use larger wheels. Fit depends on the frame, not only the wheel.
Is a 20 inch bike for what age?
A 20-inch bike is generally aimed at children around 5 to 9 years old, depending on height and inseam. More detail is in the kids bike wheel size guide.
What size bike for a 5’5” woman?
There is no single answer, because it depends on bike type, inseam and brand geometry. Many riders of that height look at small or medium frames, and check the manufacturer’s chart and standover clearance before buying.