Building a set of stairs is a tricky endeavor. Using a pair of brass stair gauges and a builder’s square to mark the stringer (the zigzag boards the steps and risers attach to) can make the job a little easier.

Step 1: Sand the outer edge of a 2×12 board to make it as smooth as possible. When using stair gauges, a nick or knothole along the edge could offset the measurements enough to make the stairs uneven.

Step 2: Lay the 2×12 on a solid surface and place the builder’s square on the far right side with both legs of the square hanging over the edge of the board.

Step 3: Attach a stair gauge on each of the outer edges of the square. 

Step 4: Position the square so the measurement on the inside of the right leg of the square corresponds with the desired depth of the stair tread and the measurement on the inside of the left leg corresponds with the desired height of the stair riser.

Step 5: Slide the stair gauges up the square until they butt against the edge of the 2×12. Tighten the gauges into position.

Step 6: Confirm that the inside measurements of the builder’s square correspond exactly with the desired depth and rise of the stairs.

Step 7: With the square firmly positioned, draw a straight line on the square from the inner measurement on the right leg to the opposing measurement on the outer edge. (If the inner measurement is 10” the outer measurement on the square would be 11-1/2”).

Step 8: Trace the two sides of the triangle formed by the inside of the square onto the 2 x 12.

Step 9: Move the square to the left and use a tape measure to confirm that the two edges of the triangle correspond exactly with the desired rise and run of the stairs.

Step 10: Position the square so the inner measurement on the right leg is directly over the end of the left side of the triangle that was just drawn. Confirm the line drawn on top of the right leg of the square is parallel with the left side of the triangle.

Step 11: Trace the inside angles of the square and continue the process, sliding the square to the left, until there are enough riser and tread marks to form the steps on the stringer.