Measuring your stairs is a very straight forward process. All you will need is good quality metal tape measure.

1 - Overall length of staircase. This should be a straight measurement from the nose of the top step, to the floor at the foot of the stairs, parallel to the sides of the stairway.

2 - Width of Stairs.
You may find that your stairs width varies a little, over the length of the stairway. Measure at its narrowest point.