FWIW basic guideline
Green Speed. Multiplier
Take your distance times the multiplier that’s the basic equation. However, some tweaks you will need to apply depending upon a bunch of factors, most of which you will need to work out based upon your style, your putter, elevations, specific greens, etc...
For every factor of elevation change plus or minus 1 for each inch and add to or subtract from your calculated distance.
These percentages work for all green speeds up to a distance of about 15’ Above 15’ you need to reduce the total by a percentage. Start with a 10% reduction and experiment.
Elevation changes greater then +/- 4” you will need to adjust your calculated number.
Inside 10’ add 1’, 1.5’, or 2.0’ (your preference) to your calculated distance to hold the line.
This should give you some basics to work with and you can modify as required. One suggestion for practice. Play practice rounds with putter pal and the green assist bar turned on. When you putt, you calculate the shot and see where your calculated putt distance falls within the green bar’s recommended putt distance. This will help you hone in your putting calculations because as you will see different greens putt differently, the greens at OLY or MER do not respond the same as the greens at BPB or WC.
Just takes some time and practice.