Stair stringer, tread, and riser calculator
Calculate the number of steps, riser height, tread depth, and stringer length for your stair project.
Stairs calculator
Choosing Stair Materials
Stair material affects safety, durability, and appearance. Building code requirements (typically 7–7.75 inch risers, 10–11 inch treads) should be your primary guide for dimensions.
Treated Lumber: The most economical choice for exterior stairs, deck stairs, and utility stairs. Pressure-treated pine resists rot and insects. Treads are typically 2x6 or 2x12 boards, and stringers are cut from 2x12 treated lumber.
Hardwood: Oak, maple, or walnut for interior stairs where appearance matters. Hardwood treads and risers provide a premium look and excellent durability. More expensive and requires finishing (stain and polyurethane).
Concrete: Poured concrete stairs are common for front entrances and commercial applications. Extremely durable and low-maintenance but expensive to form and pour. Can be finished with broom texture, exposed aggregate, or tile.
Metal Stair Stringers: Steel or aluminum stringers paired with wood, concrete, or metal treads. Metal stringers eliminate rot concerns for exterior stairs and can span longer distances than wood stringers. Often used for modern and industrial designs.
Stair Material Cheat Sheet
Use this reference to choose stair materials:
| Material | Best For | Durability |
|---|---|---|
| Treated Lumber | Exterior stairs, deck stairs, utility stairs | Moderate (needs sealing) |
| Hardwood | Interior stairs, entryways, high-end homes | High (with proper finish) |
| Concrete | Front entrances, commercial, exterior landings | Very high |
| Metal Stringers | Modern homes, exterior stairs, long spans | High (rot-proof) |
Building code requirements
- Maximum riser height: 7-3/4 inches (IRC)
- Minimum tread depth: 10 inches (IRC)
- Minimum tread width: 36 inches for main stairs
- Handrail required: 4 or more steps
- Headroom: Minimum 6 feet 8 inches
The calculator aims for riser heights close to 7 inches, which is the most comfortable and code-compliant standard for most stairs.
Worked example
For example, for a 8-ft total rise over 10-ft total run, with 7-in riser height:
- Steps = 8 ÷ (7 ÷ 12) = 13.7 → 14 steps
- Actual riser height = 8 ÷ 14 = 0.571 ft = 6.86 in
- Tread depth = (10 × 12) ÷ 14 = 8.57 in
- Stringer length = √(8² + 10²) = 12.81 ft
- Building code typically requires risers 4-7.75 in and treads at least 10 in
Common mistakes
| Mistake | Why it matters |
|---|---|
| Not following local building codes | Most codes require risers between 4 and 7.75 inches and treads at least 10 inches deep |
| Making inconsistent riser heights | All risers must be within ⅜ in of each other — uneven steps are a tripping hazard |
| Forgetting to account for tread thickness | The actual tread cuts on the stringer need to subtract the tread material thickness |