To measure the floor for carpets, the width and the length of the room must be measured, then a margin of excess should be added to all edges. Measure the width of the room and the length of the room, and add four to six inches to each of these measurements. To measure carpet for stairs, measure the width of the stair from balister to skirtboard. The length of the piece of stair carpet depends on the method of carpeting the stairs. The length and the width can each be converted to linear feet, then multiplied together to get the square footage of area of carpet.

Length of Stair Carpet

The length of the stair carpet is measured by first measuring an individual stair tread and riser. The tread is the horizontal face of the stair which is stepped on, and the riser is the vertical face of the stair which connects the front edge of one tread to the back edge of the tread below it. Measure the width of the stair tread from its junction with the bottom of the riser above it over the nosing at the front edge of the tread down the height of the riser below it down to the bottom of the lower riser. Be sure to include the nosing of the tread in its width. Add an inch to this measurement. Multiply this individual measurement by the number of stairs, then add the length of the landing at the bottom.

Winding or Turning Stairs

If any of the stairs are winding or turning stairs, the tread will be wedge shaped. Measure each of these wedge shaped stairs individually. The width of the tread will be measured at the wide end of the tread. Add this width to the height of the stair and add an inch for the length of the individual wedge stair. Add the lengths of the individual wedge stairs to the total length of the straight stairs and add six inches to the total.

Carpeting Stairs Individually

If the stairs are to be carpeted individually, there are three ways that the length of each individual stair can be measured for carpeting. To carpet only the treads, measure from the junction of the tread and the bottom of the riser above it, across the face of the tread, over and around the nosing, to the junction of the underside of the tread to the riser below it, then add an inch. To carpet both the tread and the riser of the stair, add the height of the riser to this measurement.