Stair Calculator
Calculate stair riser height, tread depth, and stringer angle.
This stair calculator computes stair rise and run, riser height, tread depth, and stringer length from your total vertical rise and available horizontal run - the stair stringer calculator math needed to keep steps code-compliant and comfortable to climb.
Enter your total rise (floor-to-floor height) and desired number of steps, and the calculator returns riser height, tread depth, and stringer angle.
Worked Calculation Examples
| Scenario | Result | Calculation Step |
|---|---|---|
| 108 in total rise over 15 steps, 150 in run over 15 treads | Riser 7.2 in · Tread 10 in · Angle ≈ 35.8° | Riser = 108 ÷ 15 = 7.2 in. Tread = 150 ÷ 15 = 10 in (7.2 + 10 = 17.2, within the comfortable 17-18 in range). Angle = arctan(108 ÷ 150) ≈ 35.8°. |
| 96 in total rise over 13 steps, 130 in run over 13 treads | Riser ≈ 7.38 in · Tread 10 in · Angle ≈ 36.4° | Riser = 96 ÷ 13 ≈ 7.38 in. Tread = 130 ÷ 13 = 10 in (7.38 + 10 ≈ 17.38, still within range). Angle = arctan(96 ÷ 130) ≈ 36.4°. |
How to Calculate Stair Rise and Run
Divide the total vertical rise by the number of steps to get riser height (commonly targeted around 7-7.75 inches per code), and divide the total horizontal run by the number of treads to get tread depth (commonly 10-11 inches). Building codes typically require consistent riser heights throughout a staircase, since uneven steps are a common trip hazard. Most residential building codes cap riser height around 7-7.75 inches and require a minimum tread depth around 10 inches, limits derived from decades of accident research showing that steps outside this comfortable range - particularly inconsistent ones within the same staircase - significantly increase the likelihood of a misstep.
The 7-11 Rule of Thumb
A widely used comfort guideline for stairs is that riser height plus tread depth should total roughly 17-18 inches - a common example is a 7-inch riser with an 11-inch tread. Steeper stairs (taller risers, shallower treads) feel harder to climb, while shallower stairs (shorter risers, deeper treads) take up more horizontal floor space.
How to Use the Stair Calculator
- Open the Stair Calculator and enter the values requested in the input fields.
- Check the units, percentages, dates, or time periods before reading the answer.
- Review the instant result and adjust any value to compare another scenario.
- Use the formula, example, and FAQs below to understand how the stair calculator works.
Frequently Asked Questions
How do I calculate stair rise and run?
Divide the total vertical rise by the number of steps for riser height, and divide the total horizontal run by the number of treads for tread depth.
What is a standard stair riser height?
Most building codes cap riser height around 7-7.75 inches, with a common design target near 7 inches for comfortable, code-compliant stairs.
What is the 7-11 rule for stairs?
It is a comfort guideline suggesting riser height plus tread depth should total around 17-18 inches - a common combination is a 7-inch riser paired with an 11-inch tread.
How do I use this stair calculator?
Enter the known values, review the units or settings, and the calculator updates the result instantly. The formula and example on this page show how the answer is produced.
What does the Stair Calculator calculate?
Calculate stair riser height, tread depth, and stringer angle. It is designed for fast browser-based calculations without sign-up, downloads, or manual spreadsheet setup.
What formula does this stair use?
The formula is: Riser Height = Total Rise ÷ Steps; Tread Depth = Total Run ÷ Treads; Stringer Angle = arctan(Total Rise ÷ Total Run). Total Rise is the full floor-to-floor height the staircase climbs, and Steps is how many risers you divide it into. Total Run is the horizontal distance the staircase covers, and Treads is how many tread surfaces you divide it into. The stringer angle comes from basic trigonometry, treating the staircase as the hypotenuse of a right triangle formed by the total rise and total run.
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Last updated: September 29, 2026.