Bike size calculator
Enter a height and see which bike fits: wheel diameter for a child, frame size for an adult, and an indicative saddle height calculated from the inside leg measurement using the LeMond formula. Works in inches and feet or in centimetres, whichever you switch to.
This is an estimate built on typical size ranges. Geometry differs between models, so the manufacturer's size chart always takes precedence over any calculator.
How does this calculator size a bike?
The ranges come from the sizing charts bike manufacturers publish for their own geometry, cross-checked between several brands. For children it matches wheel diameter to height, because a child's bike is sold by wheel size, not frame size. For adults it matches frame size to height and bike type, since a 54 cm road frame and a 17 inch mountain frame fit very different riders.
Treat the output as a starting point. Two frames with the same nominal size can differ by two centimetres of reach, which matters far more than the label on the seat tube. Always compare the result against the geometry chart for the exact model, and if you are between sizes, let your inside leg and your riding position decide: shorter frame for a racier fit, longer for touring comfort.
Once the frame is settled, set the saddle properly with the saddle height calculator, which shows the LeMond, Hamley and heel methods side by side, and get your tire pressure right before the first ride.
Frequently asked questions
- What size bike do I need for my height?
- For adults, frame size follows height and bike type: a 170 cm (5 ft 7 in) rider is typically on a 52-54 cm road frame or a 17-18 inch mountain frame. For children, size is set by wheel diameter rather than frame: 16 inch wheels at 100-120 cm, 20 inch at 110-135 cm. This calculator gives the range, and the manufacturer's own chart always wins.
- How do I measure my inseam for a bike?
- Stand barefoot against a wall and pull a book up between your legs as if it were a saddle. Measure from the top edge of the book to the floor. That number drives saddle height and helps you choose between two frame sizes when your height falls on the boundary.
- What if I am between two bike sizes?
- For children, size down: being able to put both feet on the ground builds confidence, and a bike bought to grow into is the most expensive mistake in cycling. For adults, let the intended use decide. Racier position and shorter reach point to the smaller frame; touring, commuting and a more upright position point to the larger one.
- How do I calculate saddle height?
- The LeMond method is the usual starting point: multiply your inside leg measurement by 0.883 and set that distance from the centre of the bottom bracket along the seat tube to the top of the saddle. Refine it over the first few rides. Pain at the front of the knee usually means the saddle is too low, pain behind the knee means it is too high.