Measure the height of the stairs to calculate how many boxes you need to build. Box stairs are ideal for one to three steps. The minimum tread depth is 10 inches and the maximum riser height is 8 inches.
Cut two 2-by-6-inch boards to the correct width of your stairs. Cut the other two boards to an appropriate length, according to the measurement you took in Step 1. For example, if you have two stairs, the bottom step will require a minimum tread depth of 20 inches. Therefore, you should cut the two side boards to 20 inches each.
Screw the 2-by-6-inch boards together to make a right-angled box. One board makes one side of the box.
Cut the 1 1/4-inch-by-6-inch boards to the width of your stairs.
Fasten the 1 1/4-by-6-inch board to the top of the box to make the treads.
Repeat Steps 1 through 4 for to make a second box. Place the second box in position on top of the first box, then screw the boxes securely together up through the base of the second box. Complete Step 5 for the topmost box.