ganak.appStair Calculator
Calculate stair dimensions instantly. Get riser height, tread depth, stringer length, stair angle, and building code compliance with an interactive diagram.
Total Rise: 108 in
Stair Profile
Side view with dimensions — updates as you adjust inputs
14 steps (12 shown) · Total Run: 136.5 in
Stair Dimensions
All measurements for your staircase
Comfort Score
Based on the 2R + T rule (Blondel's formula)
25.93
2R + T
good
Good comfort (23–26"). Close to ideal.
2 × 7.71″ + 10.5″ = 25.93"
Building Code Compliance
Partial check — riser, tread
Riser Height
7.71 in · Max 7.75 in (IRC R311.7)
Tread Depth
10.5 in · Min 10 in (IRC R311.7)
Does not check headroom, handrail, or step-to-step variance. Always verify with your local building department — codes vary by jurisdiction.
Calculation Breakdown
Step-by-step calculation details
| Measurement | Value |
|---|---|
| Total Rise | 108 in |
| Number of Steps | 14 |
| Riser Height | 7.71 in |
| Tread Depth | 10.5 in |
| Total Run | 136.5 in |
| Stringer Length | 174.06 in |
| Stair Angle | 36.3° |
| Comfort (2R+T) | 25.93" — good |
What Is a Stair Calculator?
Overview of the tool and what it helps you calculate.
A stair calculator determines the number of steps, riser height, tread depth, stringer length, and stair angle from your total rise measurement — so you can design and build stairs that are comfortable, safe, and code-compliant.
7.5"
ideal riser
Most comfortable
10.5"
ideal tread
Standard depth
30–37°
ideal angle
Safe & comfortable
Stair Calculation Formulas
Core formulas used for stair geometry and comfort.
Step 1.Number of steps
Step 2.Actual riser height
Step 3.Total run
Step 4.Stringer length
Step 5.Stair angle
Step 6.Comfort rule
⌈⌉ means round to the nearest whole number that keeps riser height closest to your ideal.
Building Code Requirements (IRC 2021 R311.7)
Residential stair code limits — always verify with your local authority.
| Requirement | Limit |
|---|---|
| Max Riser Height | 7¾ in (196.9 mm) |
| Min Tread Depth | 10 in (254 mm) |
| Max Step Height Variance | ⅜ in (9.5 mm) |
| Min Headroom Clearance | 6 ft 8 in (2032 mm) |
| Min Stair Width | 36 in (914 mm) |
| Nosing Range | ¾–1¼ in |
| Handrail Height | 34–38 in |
The IRC (International Residential Code) applies to most US residential construction. Local jurisdictions may have stricter requirements.
Stair Calculator Examples
Common stair scenarios with calculated dimensions.
Standard 9 ft Ceiling
36.3°
stair angle
Total rise: 108 in (9 ft)
14 steps · 7.71" rise · 10.5" run
Deck Stairs (3.5 ft)
33.7°
stair angle
Total rise: 42 in (3.5 ft)
6 steps · 7" rise · 10.5" run
Basement (10 ft Ceiling)
35.5°
stair angle
Total rise: 120 in (10 ft)
16 steps · 7.5" rise · 10.5" run
Low Deck (2.5 ft)
35.5°
stair angle
Total rise: 30 in (2.5 ft)
4 steps · 7.5" rise · 10.5" run
Common Mistakes When Building Stairs
Avoid these errors to build safe, comfortable stairs.
Measuring total rise to the subfloor instead of the finished floor — this can throw off every step by the thickness of the flooring material.
Forgetting tread thickness affects the first step — in standard mount, the bottom riser is shorter by the tread thickness.
Uneven riser heights — the IRC allows only ⅜" maximum variance between steps. Measure and mark precisely.
Building too steep — angles above 37° feel uncomfortable and unsafe. Keep treads at 10"+ to maintain a safe angle.
Not checking local codes — the IRC is a baseline, but your city or county may have stricter requirements.
Ignoring the comfort formula — 2R + T should equal 24–25 inches. Outside this range, stairs feel either cramped or stretched.
Pro Tips for Stair Construction
Practical advice for accurate stair building.
Measure total rise in at least 3 spots — floors are rarely perfectly level. Use the largest measurement for your calculation.
Use a 2×12 for stringers up to 13 steps. Beyond that, you may need an intermediate landing or engineered lumber.
Cut a test stringer first and check it before cutting the rest — it's much cheaper to waste one board than three.
Mark your layout line on the stringer with a framing square and stair gauges for consistent, accurate cuts.
For decks, count the ground as the first tread — this means one fewer tread piece to cut than the number of risers.
Use three stringers for stairs wider than 36 inches — this prevents the treads from bouncing under foot traffic.
Frequently Asked Questions
Common questions about stair calculation and building codes