No time for rack space math. Use our rack ruler instead. It's a genuinely handy tape measure incremented in both rack spaces (red) and inches (black) down to 1/32" scale. Measuring 1/2" wide by 96" (8 feet) long, its Mylar-coated retracting steel tape is housed in a tough ABS case with a thumb lock and belt clip. This is a rugged tool, not a toy.
Rack Ruler 96''Tape Measure, Legrand Group ADI, Middle Atlantic