How to measure total rise
Every stair layout starts with one number: the total rise, which is the vertical distance from the finished surface at the bottom to the finished surface at the top. "Finished" matters. If you are adding hardwood upstairs or a tile landing downstairs, include those thicknesses.
- For interior stairs, measure from the lower finished floor to the upper finished floor.
- For deck stairs, measure from the top of the deck boards straight down to where the bottom step will land. If the ground slopes, use a level and a straight board to measure at the actual landing spot, not at the deck edge.
- Measure in inches, to the nearest 1/8 in if you can.
The math behind the calculator
The calculator divides the total rise by your maximum riser height and rounds up to get the number of risers. It then divides the rise evenly so every step is the same: riser = total rise ÷ risers. There is one fewer tread than risers because the top floor acts as the last step. Total run = treads × tread depth, and the stringer length is the diagonal: √(rise² + run²).
Worked example
A basement stair with 108 in of total rise, a 7¾ in maximum riser and 10 in treads:
- 108 ÷ 7.75 = 13.9, rounded up to 14 risers
- 108 ÷ 14 = 7.71 in per riser
- 13 treads × 10 in = 130 in of total run (10 ft 10 in)
- Stringer: √(108² + 130²) ≈ 169 in, about 14.1 ft
- Angle: about 37.6°
That means a 16 ft board for each stringer, giving room for the cuts at the top and bottom. Make sure you have 130 in of floor space plus a landing area at the bottom before you commit.
Code guidance and comfort
The International Residential Code, which many US jurisdictions adopt, typically limits riser height to 7¾ in and requires a minimum tread depth of 10 in for homes. It also typically requires risers within a flight to vary by no more than 3/8 in. Local codes can differ, and handrail, headroom and guard rules also apply, so check with your building department before you build. For comfort, many builders aim for a rise of about 7 in and a tread of about 10–11 in.
Common mistakes
- Forgetting finished flooring. Adding ¾ in hardwood at the top after the stairs are built makes the top riser shorter than the rest, which is a trip hazard.
- Not dropping the stringer. At the bottom, the stringer is usually cut down by the thickness of one tread so the first step comes out the same height as the others.
- Measuring the rise at the wrong spot on sloped ground.
- Using too few stringers. Wide stairs need more stringers. Spacing depends on tread material; composite decking makers often specify closer spacing than wood. Check the product's instructions.
Buying tips
Stringers are usually cut from 2×12 lumber, because a 2×10 often leaves too little wood below the notches. Buy the next standard length longer than the calculator's stringer length (lumber is commonly sold in 2 ft steps such as 12, 14 and 16 ft). Pressure-treated lumber rated for ground contact is a common choice for outdoor stairs. Pre-cut stringers are sold at home centers in common step counts, but check that their rise and run match your numbers.
Lock your square for repeat stringer cuts