Always allow for an additional length equal to the depth of the bottom stair riser when estimating for stair carpet. Add this length to the combined length of one tread and riser multiplied by the number of stairs. Turn the extra length against the last riser covered and. When wear occurs. Move the carpet and turn the surplus against the riser at the opposite end. This considerably lengthens the life of the carpet.
If the staircase includes winding stairs each winding tread must be measured separately at its widest point to get an accurate estimate.