We want to put rubber down under our squat rack in the basement. Would you use 1/4 inch or 3/8 inch over top of a Berber carpet?

Our 1/4" Regrind Rolls are plenty under a squat rack. Since plates diffuse more of the weight, a 1/4" roll typically is good enough for a home gym. If you are really concerned about the plates damaging your subfloor, you can use our 3/8" thick rubber, but it's not necessary. 3/8" thick rubber is the most common thickness used in commercial gyms.