Pick the bike type, enter your height and, if you have it, your inseam. The calculator suggests a frame size range and a starting saddle height. Nothing you type leaves your browser.
How This Calculator Works
The size letter comes from a height chart that matches the ranges most large brands publish for road, mountain and hybrid frames. Brands do not agree exactly, so treat the size as a range to look at rather than a single answer.
When you add an inseam, two common rules of thumb are applied:
- Road frame size: inseam in centimeters x 0.665. This approximates a traditional seat tube length.
- Mountain and hybrid frame size: inseam in inches x 0.685, minus about 4 inches for mountain bikes to leave room over the top tube.
- Saddle height: inseam x 0.883, measured from the center of the crank axle to the top of the saddle along the seat tube. This is often called the LeMond method.
How to Measure Your Inseam
Stand barefoot with your back against a wall and your feet about 6 inches apart. Pull a hardcover book snugly up between your legs, spine up, as a saddle would sit. Mark the top of the spine on the wall and measure from the floor to the mark. Repeat twice and use the average.
Limitations
Seat tube length is only one part of fit. Reach and stack, which describe how far forward and how high the handlebars sit, matter just as much and vary a lot between models with the same size label. Long arms, a short torso or flexibility limits can move you up or down a size. If you are between sizes, the smaller frame is usually easier to adjust with a longer stem or seatpost, while the larger frame is harder to shrink.
For a pricey bike, a professional fit or a test ride in the shop is worth more than any chart.
Frequently Asked Questions
Should I trust height or inseam more?
Inseam is a better guide for standover and saddle height, while height is closer to how most brands label their sizes. When the two disagree, check the specific bike geometry chart for standover height and reach.
What if I am between two sizes?
Riders with longer legs for their height often fit the larger size, and riders with a longer torso the smaller one with a longer stem. A test ride settles it faster than any formula.
Do kids bikes use the same chart?
No. Kids bikes are sized by wheel diameter, from 12 to 24 inches, and the maker’s chart based on inseam is the best guide.
Why do some brands use S, M, L and others use numbers?
Road frames were traditionally sized by seat tube length in centimeters and mountain frames in inches. Many brands now use letter sizes, but the numbers still appear on geometry charts.