Does anybody know the strut length to ride height conversion?
 

I just bought a set of coilover but I don't how long I should set it to. I just want to lower my car for like 1.5 inches. Thanks alot !!!

adjust all coilovers to the same length
install ur coilovers
then adjust afterward

I set mine so that they fit in easily and then lowered the car down from there after they were installed. Its not hard to adjust the height.

There is no universal measurement you are looking for. All are different and will compress differently. The only way to set it is to put it on and work from there. Best way to measure is from the center of the wheel to the highest point of the fender arch to compare amount lowered and side to side. Front to back, you can check the frame rail or just look at it. Beyond that, you would have to have it cornerweighted to get it any better