Bike Size Calculator
Getting the right frame size is the single biggest factor in whether a bike feels comfortable and rides well, and it comes down mostly to your leg length rather than your overall height. This calculator uses the standard inseam method to suggest a frame size for a road, hybrid or mountain bike. Your inseam is the distance from the floor to your crotch, measured in bare feet, and it drives the calculation because it sets how far the saddle sits above the pedals and how much standover clearance you have over the top tube. Choose the type of bike you are sizing, enter your height and inseam in centimetres, and the calculator returns a recommended frame size, a size band from extra small to extra large based on your height, and a saddle height to set as a starting point. Road frames are measured in centimetres, hybrids in centimetres, and mountain bikes traditionally in inches, so the result is given in the unit that matches the type you pick, with the other unit shown alongside. Treat the figure as a well-informed starting point rather than a precise answer, because frame geometry varies between brands and models, and two bikes with the same labelled size can fit quite differently. Where you can, take a test ride and check the standover clearance and reach, and if you are between sizes think about whether you prefer a more upright or a more stretched-out position.
For a road bike, a rider 175 cm tall with an inseam of 80 cm suits a frame around 53.2 cm (size M).
Frame sizing varies between brands, so use this as a starting point and test ride where you can. Saddle height uses the LeMond method (inseam times 0.883). Estimate only.
How it works
The recommended frame size comes from the inseam method: for a road bike the frame size in centimetres is your inseam times 0.665, for a hybrid it is your inseam times 0.685, and for a mountain bike the frame size in inches is your inseam times 0.226. The size band from extra small to extra large is read off your overall height, which is how most manufacturers label their charts. The saddle height is the LeMond formula, your inseam times 0.883, measured from the centre of the bottom bracket to the top of the saddle, which sets your leg to a good extension at the bottom of the pedal stroke.
Worked example
A rider 175 cm tall with an 80 cm inseam is sizing a road bike. The frame size is 80 × 0.665 = 53.2 cm, which in inches is 53.2 / 2.54 = 20.9. A height of 175 cm falls in the medium band. The saddle height to start from is 80 × 0.883 = 70.6 cm. So this rider should look at a road frame around 53 to 54 cm, in a size medium, and set the saddle near 70.6 cm before fine-tuning. Switch the type to a mountain bike and the same inseam suggests a frame of 80 × 0.226 = 18.1 inches.
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