Stair Calculator
Calculate riser height, tread depth, stringer length, angle and number of steps. Includes IRC guidelines and live diagram.
Last updated: September 2026 · Reviewed against IRC R311.7 residential stair requirements
Stair Stringer Layout Diagram
This diagram shows the basic layout of a stair stringer with rise, run, and stringer length.
How to Use This Stair Calculator
- Enter the Total Rise (vertical height from finished floor to finished floor)
- Optionally enter a preferred riser height (most comfortable is 6.5" – 7.75"; default is 7.5")
- Enter desired tread depth (usually 10" – 11"; default is 10")
- Leave Number of Steps blank to auto-calculate, or enter a specific count
- Click Calculate Stairs to get number of risers, exact riser height, total run, stringer length, angle, and IRC warnings. A live diagram updates automatically.
Common Stair Examples (10" Tread)
Quick reference for typical floor-to-floor heights using a 10-inch tread and target riser near 7–7.5". Actual riser is adjusted to divide the total rise evenly. Stringer length is approximate.
| Total Rise | Risers | Actual Riser | Total Run | Stringer (approx.) | Angle |
|---|---|---|---|---|---|
| 8 ft (96") | 13 | 7.38" | 120" | 13.3 ft | 38.7° |
| 9 ft (108") | 14 | 7.71" | 130" | 14.5 ft | 39.7° |
| 10 ft (120") | 16 | 7.50" | 150" | 16.2 ft | 38.7° |
| 11 ft (132") | 18 | 7.33" | 170" | 17.9 ft | 37.8° |
| 12 ft (144") | 19 | 7.58" | 180" | 19.0 ft | 38.7° |
Always re-calculate with your exact total rise. These are planning examples only.
IRC Stair Code Guidelines (US)
| Measurement | Recommended / Code Limit |
|---|---|
| Maximum Riser Height | 7.75 inches (197 mm) |
| Minimum Tread Depth | 10 inches (254 mm) |
| Minimum Headroom | 6 ft 8 in (2032 mm) |
| Ideal Riser Height | 6.5" – 7.5" |
| Ideal Tread Depth | 10" – 11" |
| Riser Height Variation | Max ⅜ inch between any two risers |
Always check your local building codes. These are general IRC R311.7 guidelines for residential stairs. For deck area and landing size, try the square footage calculator.
Formulas Used
Number of Risers = Total Rise ÷ Desired Riser Height (rounded to nearest whole number)
Actual Riser Height = Total Rise ÷ Number of Risers
Number of Treads = Number of Risers − 1
Total Run = Number of Treads × Tread Depth
Stringer Length = √(Total Run² + Total Rise²)
Angle = arctan(Total Rise ÷ Total Run)
How to Design Comfortable Stairs
Good stairs feel natural underfoot. The relationship between riser height and tread depth is the key to comfort and safety.
The 7-11 Rule & Comfort Checks
A common rule of thumb is a 7-inch riser with an 11-inch tread. Many codes allow up to 7.75" risers and require at least 10" treads. Two useful comfort checks:
- Rise + Run ≈ 17–18 inches — keeps the stride natural
- 2 × Rise + Run ≈ 24–25 inches — classic safety / comfort formula
Stringers
Stringers are the diagonal boards that support the treads and risers. Most residential stairs use three stringers (two outer + one center). Space them no more than 16 inches on center for ¾-inch treads. Cut them from the calculated stringer length; buy the next standard board length up and leave a few extra inches for the bottom and top cuts. If your landing or deck needs a concrete pad, use the concrete calculator for volume and bags.
Headroom
Maintain at least 6 ft 8 in of clear headroom above the nosing line of the treads for the full width of the stairway.
Tips for Building Stairs
- Keep all risers the same height (variation must be less than ⅜")
- Use a comfortable riser height between 6.5" and 7.75"
- Deeper treads (10–11") feel safer and more comfortable
- Add a landing if the total rise is more than about 12 feet
- Always verify measurements on site before cutting stringers
- Order stringer stock longer than the calculated length to allow for layout and cuts
Frequently Asked Questions
Related measurements
Stairs often connect to decks, landings, and floors. Estimate landing or deck area with the square footage calculator, footing volume with the concrete calculator, and finish materials with the flooring calculator or paint calculator. Browse all construction calculators on EntireCalc.