Your body
Measure barefoot, in mm. Unsure? Enter height and press Estimate, then refine what you can measure.
Riding
How to measure
- Inseam — stand against a wall, feet 15–20 cm apart, pull a hardback book firmly up into the crotch, measure floor → top of the book spine.
- Torso — with the book still in place, measure book spine → sternal notch (the V at the base of your neck).
- Arm — arm hanging straight, from the bony tip of the shoulder (acromion) to the centre of your closed fist.
- Shoulder width — acromion to acromion (bony tips), measured across the back.
- Sit-bone width — sit on corrugated cardboard on a hard step, lean forward, measure centre-to-centre of the two dents.
Your bike
Copy these numbers from the manufacturer's geometry chart for your exact size. Stack and reach matter most.
Parts that matter for fit
Adjust your current setup
Enter how your bike is set up now, then drag the sliders and watch the joint angles react. Saddle height = BB centre → top of saddle where you sit. Setback = saddle nose horizontally behind BB.
Camera analysis
Put the bike on a trainer, camera at hip height, exactly side-on, 2.5–3 m away, whole body in frame. Tight clothing & good light help. Pedal steadily for 20 s. Everything runs on your device.
How it works
Bike Fit Lab builds a side-view skeleton of you from your measurements, places it on your bike's real geometry, and solves every joint through a full pedal stroke with inverse kinematics. It then searches saddle height, setback and cockpit (stem length, angle, spacers) to land your joints inside evidence-based target ranges for your riding style.
What it combines
- Holmes / dynamic knee-angle method — saddle height is solved for ~30–37° knee flexion at the bottom of the stroke (Holmes et al., 1994; Bini et al., 2011 review). Shown alongside the LeMond (0.883 × inseam) and Hamley & Thomas (109 % inseam, 1967) formulas for reference.
- KOPS — knee over pedal spindle at 3 o'clock as the starting point for saddle setback, shifted per style (forward for TT, slightly forward for MTB).
- Anthropometric segment ratios (Winter, Biomechanics and Motor Control of Human Movement) to split leg, torso and arm into segments.
- Stack / reach cockpit trigonometry — the same maths behind tools like Slowtwitch's F.I.S.T. calculator, XY Bike Calc and bike-size.com's stem comparison, including the head-angle effect on spacers.
- Google MediaPipe Pose Landmarker (open source, Apache-2.0) for markerless video analysis in the browser, as used in open-source bike-fitting research projects. Published validation puts MediaPipe knee angles within roughly ±6° of marker-based tools, so treat video numbers as a guide and average over many strokes.
Calibrating
No model knows exactly where your hip joint sits on the saddle. In the Camera tab, after measuring your real knee angle on your current setup, press Calibrate model: the hip offset is adjusted so the model matches reality, and every recommendation becomes personal.
Limits
This is a self-fit tool, not medical advice. Make changes in small steps (≤ 5 mm saddle height at a time), ride a few days between changes, and see a professional fitter or physio if you have pain, injury, leg-length difference or numbness.
Data
Everything is saved in your browser only.