Online Tool Store
Bike Frame Size Calculator
Estimate the right frame size from inseam and height for road, gravel, and mountain bikes, with the geometry figures that matter more than size labels.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
Health & Fitness
Bike Frame Size Calculator
Frontend preview — no upload or external service.
Suggested size
178 cm with an 84 cm inseam on a road bike: 55-56 cm frame, or a medium. Stack around 570 mm and reach around 385 mm matter more than the label.
How the Bike Frame Size Calculator works
- Measure inseam properly — barefoot, book pressed firmly up against the crotch, floor to top of book.
- Read the suggested size as a starting point for which frames to test ride.
- Compare stack and reach on the actual geometry chart, since two bikes labelled medium can differ by centimetres.
The method
Frame size labels are inconsistent between manufacturers, but stack and reach describe the same thing on every bike.
stack = vertical distance bottom bracket to head tube top; reach = horizontal distance
Two bikes both labelled 56 cm can differ by 20 mm of reach, which is the difference between a comfortable fit and a bike you never enjoy riding.
FAQ
Why are frame sizes so inconsistent?
Because manufacturers measure differently — seat tube length, effective top tube, or an arbitrary label. Stack and reach are measured the same way by everyone, which is why fitters use them.
Between two sizes, which should I choose?
It depends on flexibility and intended use, and it is genuinely a case for a test ride. Sizing down and using a longer stem gives a different handling feel from sizing up, even at the same effective reach.
Is a professional bike fit worth it?
For anything beyond casual riding, usually yes. Sizing gets you the right frame; a fit adjusts saddle height, setback, bar position and cleats, which is where comfort and power actually come from.
How we compare
| Feature | Online Tool Store | A paper log | A subscription health app |
|---|---|---|---|
| Stack and reach explained | ✓ | Size label only | Yes |
| Bike type specific | ✓ | ✓ | ✓ |
| No shop visit needed | ✓ | ✗ | ✗ |
| Replaces a bike fit | ✗ | ✗ | ✗ |
Bike Frame Size Calculator points at stack and reach, because two bikes with the same size label can fit completely differently.