How to work out stair stringers for deck steps

Why the usual way fails

Stairs look simple until you do the maths. The total rise rarely divides into a neat number of equal steps, so you end up with fractions of an inch to spread across every riser. Tread depth, riser height and the angle all depend on each other, and changing one changes the rest. Many people sketch it on paper, measure off a framing square and hope, then find out the bottom step is taller than the others once it is built. And most guides online explain the theory without doing the numbers for your exact height. Then there is the number of stringers itself. Wide steps need more than two, and if you guess low the treads flex underfoot. Hiring someone to lay out three or four steps can cost more than the wood, which is why many people try it themselves and learn the hard way on the first stringer.

How BuildRuler - Free material calculators helps

BuildRuler is a free set of calculators for home and yard projects, and its stair stringer calculator gives you riser height, tread count and stringer length along with a cut diagram. There is also a general stair calculator for steps, run and angle. Each calculator shows the formula it uses and draws your project to scale, so you can see if the input makes sense before you cut. There is no sign-up and no email, and it works in a mobile browser, which helps when you are measuring outside. Once the stairs are planned, the same site can also price the lumber list.

Step by step

1. Measure the total rise from the top of the deck to the ground where the stairs will land.
2. Open the stair stringer calculator on BuildRuler and enter that rise and the tread depth you want.
3. Read the riser height, tread count and stringer length it gives back.
4. Check the cut diagram against your measurement so the drawing matches what you expect.
5. Use the board foot or lumber calculator to price the boards for the stringers and treads.

Tips

• Measure the rise at the exact spot where the bottom step will land. Ground slopes, and an inch of difference there shows up as an uneven last step.
• Cut one stringer first, test it in place with a level on each tread, and only then use it as a template for the others.
• Treat the numbers as a plan and check your local building code for riser and tread limits before you build.
• If your lumber yard quotes different prices from the defaults, swap in their figures so the cost estimate matches what you will pay.

Questions