Dial in saddle height with LeMond, Holmes, or Hamley.

LeMond (0.883 x inseam) is the most quoted starting point and is what most bike shops have used for forty years. Holmes is the upgrade - it subtracts crank length, which actually matters because your foot finishes at a different height depending on whether you are pedalling 165s or 175s. Hamley is what most modern fit jigs show: 1.09 x inseam from the bottom-bracket centre to the top of the saddle. If you are calibrating against a real fit you got somewhere, match the formula to the measurement method that fit used.

Within 5-10mm for most riders, which is usually inside the comfort window. A real fit accounts for hip mobility, leg-length asymmetry, cleat position, and how your knee tracks under load - none of which a formula can see. Use the formula as a starting point, then bracket up and down 3-5mm over a few rides until knee feel and saddle pressure settle.

Front-of-knee pain (patellar) usually means saddle too low - your knee is over-flexing at the top of the stroke and the patella is grinding. Back-of-knee pain (hamstring/popliteal) usually means saddle too high - your knee is hyper-extending at the bottom and the back of the joint is stretching. Adjust 5mm at a time, ride three rides at the new height, reassess. Bigger jumps blow up your whole fit.

Stand barefoot against a wall, feet roughly shoulder width. Press a hardcover book firmly up into your crotch as if you were sitting on a saddle. Measure from the floor to the top edge of the book spine. Do it twice and average. Pants-inseam off a tape from a clothes shop is not the same number and will give you a saddle height that is 1-2 cm too low.

Saddle-to-bottom-bracket distance should stay close to identical across your bikes - that is the whole point of having one formula. Reach and stack will differ, and you might run a few mm lower on a TT bike for hip-angle reasons, but for road/gravel/MTB on the same cranks, match the saddle height to within 2mm and your knees will thank you.

Centre of the saddle, along the line from the bottom-bracket axle through the seat tube extended to the top of the saddle. Most modern saddle shapes have a sit-bone platform a bit behind the nose - measure to that platform centre, not to the very nose, or you will end up too high.

After any major fit change (new shoes, new cleats, new saddle, surgery, big weight change), check it. Otherwise, once per year - tendons and hip mobility shift slowly, and what fit you at 25 may not fit you at 35.

KOPS is a fore-aft fit metric, not a saddle-height metric. Set saddle height first using one of the formulas, then adjust setback so your knee is roughly over the pedal spindle at 3 o'clock. The two adjustments interact a little - if you move the saddle back, the effective height to the pedal increases by a few mm.