Quick answer
Measure from the shoulder to the floor while wearing the intended shoes, then subtract the desired hem clearance. A 145 cm measurement and 5 cm of clearance give a 140 cm shoulder-to-hem length.
Formula and assumptions
Length = shoulder-to-floor + effective heel lift − clearance. Height mode approximates shoulder-to-floor as 87.5% of height. Measure in your intended shoes for best results.
Worked example
A 144 cm shoulder-to-floor measurement with 4 cm clearance gives a 140 cm dress length.