Step 5: Determine the number of stair stringers

The quantity of stair stringers is based on how wide the stairs will be and what type of surface boards you are using. If you're using 2"x6" wood, the maximum distance between stringers should not exceed 24 inches on center. If you are using 5/4"x6" wood or composite lumber, the maximum distance between stingers should not exceed 16 inches on center.

Divide the width by 16" or 24" (based on decking material) and then add 1.

For example:
48" / 24" = 2
2 + 1 = 3 stringers