Youth and league sports sizing · Cycling
Kids bike size by height.
Child height, and an optional inseam, to the wheel size on the Trek kids’ bike chart. Bands overlap, so you may see two sizes.
Inputs
Result
Fill in the form.
How this works
Trek sizes kids’ bikes by wheel diameter, not frame size. Its chart pairs each wheel size with an age, a height and an inseam: 12 inch for ages 2 to 3, 16 inch for 4 to 6, 20 inch for 5 to 8, 24 inch for 8 to 11 and 26 inch for 10 to 12. Your height is read in whole inches against those bands. If an inseam is given, each row is marked as fitting or not. The tool does not use age, because the age ranges overlap more than the heights do.
For fit, Trek says a child should stand over the bike with 1 to 2 inches of clearance above the top tube, and that on a first pedal bike both feet should reach the ground when seated.
Worked example. A child who is 3 ft 11 in (47 in) falls in both the 16 inch band (3 ft 5 in to 4 ft 0 in) and the 20 inch band (3 ft 9 in to 4 ft 6 in) on Trek’s chart. With an inseam of 17 in the 16 inch bike fits (16 to 22 in) and the 20 inch does not (19 to 25 in). A child of 3 ft 4 in is between the 12 and 16 inch bands, so the tool shows both neighbours.
Frequently asked questions
What size bike for a 5 year old?
Trek lists 16 inch wheels for ages 4 to 6 and 20 inch for ages 5 to 8, so a 5 year old can be in either by height. Use height: 3 ft 5 in to 4 ft 0 in is the 16 inch band.
What size bike for a 4 foot child?
Four feet falls in Trek’s 16 inch band (3 ft 5 in to 4 ft 0 in), the 20 inch band (3 ft 9 in to 4 ft 6 in), and just below the 24 inch band, which starts at 4 ft 1 in.
How do I measure inseam?
The tool takes it in inches or centimetres. Trek’s chart gives inseam ranges such as 19 to 25 in for 20 inch wheels. Measure the child’s inside leg and enter it in inches or centimetres.
What if my child is between two wheel sizes?
Trek says the brackets are wide and overlap, and that bikes of the same wheel size fit differently. Test ride, and do not buy a bike that is too big.
When do kids move to an adult bike?
Trek says to start looking at adult bikes if a child is older than 12 or taller than 4 ft 8 in.
Sources
Checked
The wheel sizes, ages, height bands and inseam ranges are Trek’s kids’ bike size chart. The standover and seat-height notes are from the same page. Reading height in whole inches and showing neighbours across a gap are this tool’s own rules. Balance bikes are not on the chart. Runs entirely in your browser. Nothing you type is sent or stored.
Scope
A starting size from a published chart, not a professional fitting. Makers and leagues differ, so try equipment on, and check your league’s rules. Helmets and other protective gear are not covered.