rack cable length

This is probably a stupid question, but.... We've got a few racks in a colo. The racks don't have any decent cable management (square metal holes to attach velcro to). We either order cable too long and end up with lots of loops which get in the way (no place to loop lots of excess really) or too short to run along the side (which is worse). It appears others using the same racks have figured this out, but... Do y'all just order 10 of each size per rack in every color you need or is there a better way to figure this out? I'm guessing something like 24 inches + 1.75 inchex x Us) + 24 inches and round up to standard length...?