Stair Calculator
Stair Dimensions
14 Risers × 7.71"
Total run: 11' 4.5" | Angle: 38.4°
Risers
14
Riser Height
7.71"
Stringer Length
14' 6.1"
Stringers Needed
4
Code Compliant: These dimensions meet IRC residential building code requirements. Riser height ≤ 7¾", tread depth ≥ 10", width ≥ 36".
IRC Standards: Maximum riser height: 7¾". Minimum tread depth: 10". Minimum width: 36". Minimum headroom: 6'8". Maximum riser variation: 3/8" between any two risers.
Disclaimer: Estimates are for budgeting purposes only. Actual costs vary by location, contractor, material availability, and project complexity. Always get professional quotes for exact pricing.
Stair Dimensions Reference
| Total Rise | Risers | Riser Height | Total Run | Angle |
|---|---|---|---|---|
| 36" (3 ft) | 5 | 7.20" | 3' 6" | 40.6° |
| 96" (8 ft) | 13 | 7.38" | 10' 6" | 35.1° |
| 108" (9 ft) | 14 | 7.71" | 11' 4.5" | 36.3° |
| 120" (10 ft) | 16 | 7.50" | 13' 1.5" | 35.5° |
* Based on 10.5" tread depth, 7.5" desired riser height.
IRC Code Quick Reference
| Requirement | Minimum | Maximum |
|---|---|---|
| Riser Height | — | 7¾" |
| Tread Depth | 10" | — |
| Stair Width | 36" | — |
| Headroom | 6' 8" | — |
| Riser Variation | — | 3/8" between any two |
How We Calculate
Our stair calculator computes stair dimensions based on total rise, desired riser height, tread depth, and stair width. It calculates the number of risers, actual riser height, total run, stair angle, stringer length, and number of stringers needed.
How the math works: Number of risers = round(total rise ÷ desired riser height). Actual riser height = total rise ÷ number of risers. Total run = (risers - 1) × tread depth. Stair angle = arctan(total rise ÷ total run). Stringer length = √(rise² + run²). Stringers = max(3, ceil(width ÷ 16) + 1).
IRC Building Code Requirements
Riser Height: Maximum 7¾" (196 mm). Minimum is not explicitly stated but 4" is the practical minimum. All risers must be within 3/8" of each other.
Tread Depth: Minimum 10" (254 mm), measured from nosing to nosing. Nosing projection: ¾" to 1¼" beyond the riser face.
Width: Minimum 36" clear width above the handrail. Handrails may project up to 4.5" into the required width on each side.
Headroom: Minimum 6'8" (80") measured vertically from the stair nosing to the ceiling/header above.
Comfort Guidelines
The most comfortable stairs follow the "rule of 25": riser + tread ≈ 17"–18". For example, 7.5" riser + 10.5" tread = 18". Ideal stair angle is 30°–37°. Steeper than 40° feels uncomfortable for daily use.
Material Notes
Stair stringers should be cut from 2×12 lumber (SPF or Douglas Fir). The minimum remaining wood after notching must be 3.5". Use construction adhesive and screws to secure treads to stringers. For exterior stairs, use pressure-treated lumber or composite materials.
Last updated: 2026-02-02
Frequently Asked Questions
How do you calculate stair dimensions? +
Divide total rise (floor-to-floor height in inches) by desired riser height (7–7.75" typical) to get the number of risers. Total run = (risers - 1) × tread depth. Standard residential: 7.5" risers × 10.5" treads for a comfortable 35° angle.
What is the standard stair riser height? +
IRC code allows a maximum riser height of 7¾" (7.75"). The ideal range is 7"–7.5" for comfortable climbing. All risers must be within 3/8" of each other in height — consistency matters more than exact height.
What is the minimum tread depth for stairs? +
IRC code requires a minimum tread depth of 10". The ideal range is 10"–11" for a comfortable stride. The "rule of 25" says riser + tread should equal approximately 17"–18" for comfort (e.g., 7.5" riser + 10.5" tread = 18").
How many steps for a 9-foot ceiling? +
A 9-foot (108") ceiling typically needs 14–15 risers. With 7.5" risers: 108 ÷ 7.5 = 14.4, round to 14 risers at 7.71" each, or 15 risers at 7.2" each. Both meet code (under 7.75" maximum).
What is the ideal stair angle? +
The most comfortable stair angle is 30°–37°. Under 20° feels like a ramp, over 40° feels like a ladder. At standard 7.5" rise and 10.5" run, the angle is about 35.5° — right in the sweet spot.
How wide should residential stairs be? +
IRC requires a minimum width of 36" (3 feet) for residential stairs. 42"–48" is more comfortable and allows two people to pass. Handrails can project up to 4.5" into the required width on each side.
How many stringers do I need? +
Use a minimum of 3 stringers for 36" wide stairs. Add one stringer for every 16" of additional width. A 48" staircase needs 4 stringers. Stringers should be cut from 2×12 lumber for adequate strength.
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