Knee angle at the bottom of the stroke
The measurement saddle height is usually judged by.
DIY bike fit
The angles a fitter measures, from a clip you record yourself.
A professional fit measures joint angles at specific crank positions. You can estimate the same angles from a phone video — as long as the camera is placed properly, because every number downstream inherits a bad camera position.
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Numbers you can compare against your own clips.
Hip and torso angle
Read your actual riding position rather than the one you think you hold.
Elbow and reach
Check the front end in the hand position you actually ride in.
How you film it decides what the numbers mean.
Film the drive side with the camera at about saddle height — not on the floor — square and level to the bike, with the whole rider and both wheels in frame. Warm up first, hold one hand position, and record about 20 seconds of steady pedalling. Normal video: no slow-motion, no ultra-wide.
Estimates from a single camera are comparable when the setup is comparable. Note where you put the camera so the next clip can be shot the same way.
Straight answers, including the limits.
Why does the camera height matter so much?
Every fit number is measured at a crank position. A camera on the floor or off-square bends the pedal circle in the image, and every angle computed from it inherits that error.
Does this replace a professional fit?
No. It gives you real numbers to work from and to track between changes. A fitter brings judgement, and hands on the bike.
Should I use slow-motion?
No. Record normal video. Slow-motion and ultra-wide modes change the frame rate and the lens geometry the estimates depend on.
Other things you can measure this way.
Record one clip and see what it gives you.
The preview runs without an account. Save an analysis when you want to compare it with the next one.