Start with your height to find a frame size range, then use your inseam and a standover check to choose within it. Frame sizes are not standardized, so any general bike size chart is a first guess. The chart the maker publishes for that exact model should make the final call.
A general height to frame size chart for adult bikes
Most adult bikes come in a handful of sizes, and height is the quickest way to narrow them down. The ranges below come from the general guide that Retrospec publishes for its adult bikes, with frame size given as seat tube length in inches alongside the matching letter size.
| Rider height | Frame size | Letter size |
|---|---|---|
| 4 ft 10 in to 5 ft 2 in | 13 to 15 in | XS to S |
| 5 ft 3 in to 5 ft 6 in | 15 to 17 in | S to M |
| 5 ft 7 in to 5 ft 10 in | 17 to 19 in | M to L |
| 5 ft 11 in to 6 ft 2 in | 19 to 21 in | L to XL |
| 6 ft 3 in and up | 21 in and up | XL and up |
A rider near the edge of a range could fit either neighboring size depending on leg length and the style of bike. Mountain, road, hybrid, cruiser and electric bikes are built around different riding positions, so the same person can end up on a different size for each.
Measuring your inseam with a book against the wall
Two riders who stand equally tall can still need different frames, and inseam is the measurement that tells them apart. The inseam on your jeans is not it, because pants stop well short of where a saddle sits.
- Take off your shoes and stand with your back against a wall, feet roughly hip width apart.
- Slide a hardcover book between your legs, spine up, and lift it firmly the way a saddle would press.
- Keep the book level and mark the wall at the top of the spine.
- Measure from the floor to the mark, then repeat once and use the average.
Many makers print a standover height for every frame size in the geometry table on the product page, and comparing it with your inseam tells you how much room you will have when you stop.
Why a medium from one brand can ride like a small from another
No industry rulebook says what a medium must measure. Some makers label frames by seat tube length in inches, some in centimeters, and many now use letters. Trek, for example, has moved its road bikes from numbered sizes to letter sizes.
So use the chart above to know roughly where to look, then open the size chart for the exact model and year you are considering. If it lists a height and inseam range for each size, trust those numbers over any general table, this one included. A maker’s online size finder works from its own frame geometry, which a generic chart cannot know.
Standover clearance and reach on a test ride
Straddle the frame just in front of the saddle with both feet flat on the ground. Retrospec suggests roughly 1 to 2 inches of space between you and the top tube on most bikes, and notes that mountain bikes often allow a little more because of rougher terrain. On a step through frame there is no top tube in the way, so reach becomes the better test.
Reach is how far forward you stretch to the grips. Slightly bent elbows and relaxed shoulders are a good sign. Locked arms or a cramped, folded feeling usually mean the frame is too long or too short. If the seatpost is already raised to its limit and your legs still feel bunched up, you probably need the next size.
When you land between two frame sizes
Falling on the line between two sizes is common. Retrospec says most riders in that spot prefer the smaller frame for control and easier handling. Trek describes the choice for mountain bikes as a matter of riding style and body proportions, so a rider with long legs and a short torso may lean one way while someone with a long torso leans the other.
A shop can fine tune the fit afterward by swapping the stem or sliding the saddle on its rails, and a professional bike fit helps if rides leave you sore. Anyone shopping for a commuter bike can use the same measurements, since frame sizing works the same way whatever the bike is for.
Frequently asked questions
What size bike frame fits someone who is 5 ft 6 in tall?
On the general chart above, 5 ft 6 in sits at the top of the small to medium band, roughly a 15 to 17 inch frame. Because that height is near the edge of a range, measure your inseam and check the maker's chart for the exact model before you buy.
Is frame size the same thing as wheel size?
No. Frame size describes the length of the frame, usually measured along the seat tube, while wheel size is the diameter of the wheel. Adult bikes are chosen mainly by frame size. Kids' bikes are the exception, since they are usually sold and sized by wheel diameter instead.
Can my current bike help me pick the next size?
Yes, as a starting point. Look for a size printed on the frame, then compare that bike's geometry numbers with the new model's chart. If the old bike felt cramped or stretched, move one size in the direction that would have fixed it, and confirm with a test ride.
What size person is a 26 inch bike for?
Riders over about 5 feet tall. Schwinn treats 26 inch bikes as an adult size that also suits some tweens and teens, and says they fit riders over 60 inches tall regardless of age. The number describes the wheels, not the frame, so adults should still pick a frame size that matches their height and inseam.
What size bike does a child need?
Kids' bikes are sized by wheel diameter, not frame size. Retrospec's general chart pairs 12 inch wheels with ages 2 to 3, 16 inch with 4 to 6, 20 inch with 6 to 8 and 24 inch with 8 to 12. Age is only a starting point, so check the child's height and inseam against the maker's chart.
