Find how many square yards of carpet your rooms need. Each dimension has its own unit selector (in/ft/yd/m).
Carpet is usually sold by the square yard. Measure each room (length times width, any unit), add them up, then divide by 9 (there are 9 sq ft in a sq yard). Add about 10% for waste, seams and pattern matching. Carpet comes in fixed roll widths, so the purchase may round up to fit the layout.