Measure the length of each room at the longest point
Measure the width of each room at the widest point
Measure closets, alcoves, and other separate areas
Measure doorways and hallways if carpet will extend into them
Record all measurements in the same unit
Multiply length by width to get square footage for each area
Add all area totals together
Add extra for waste, pattern matching, and trimming
Use a larger allowance for irregular room shapes
Double-check all measurements before ordering carpet