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Stairs Calculator

Calculate stair dimensions and building code compliance

Stairs Calculator Guide

A stairs calculator computes riser height, tread depth, number of steps, total run, and stringer length from your total rise and space. It helps you plan a comfortable, code-aware staircase for interior or exterior projects.

What is Stairs Calculator?

The stairs calculator applies ergonomic rules like 2R+T ~ 24-25 in, respects typical maximum risers and minimum treads, and returns layout metrics and cut dimensions for stringers. Always confirm local code requirements.

How to Use the Stairs Calculator

  1. Measure total rise (finished floor to finished floor).
  2. Pick target riser (e.g., 7.5 in) and tread (e.g., 10.5 in).
  3. Calculate steps: risers = ceil(rise/target_riser); recompute exact riser height.
  4. Compute run: run = treads * tread_depth (treads = risers - 1 unless top tread overlaps).
  5. Check headroom & landings; adjust as needed.
  6. Output stringer rise/run increments and stringer length.

Formulas & Methods

  • Steps (risers): n = ceil(R_total / R_target); exact riser R = R_total / n.
  • Treads: typically n - 1 (if top landing acts as final tread).
  • Run: Run_total = T_depth * (n - 1).
  • Stringer length: L = sqrt(R_total^2 + Run_total^2) (per stringer).
  • Comfort: 2R + T ~ 24-25 in.
  • Angle: theta = atan(R / T_depth); typical stair angle 30-37 degrees.

Assumptions & limitations

  • Values above are guidelines; building codes vary by region.
  • Nosing, finish thickness, and flooring add to dimensions—include in rise/run.
  • Outdoor stairs may require larger treads for safety and drainage.

Examples

Example A — Interior stair
Total rise = 112 in. Target riser = 7.5 in -> n = ceil(112/7.5) = 15 risers.
Exact R = 112/15 = 7.47 in. Treads = 14; T = 10.5 in -> Run_total = 147 in.
Stringer L = sqrt(112^2 + 147^2) ~ 184 in (15.3 ft).
Comfort check: 2R + T = 2*7.47 + 10.5 = 25.44 in (within range).

Example B — Exterior with landing
Rise = 72 in, target = 7.25 in -> n = 10 risers, R = 7.2 in.
Treads = 9, T = 11 in -> Run = 99 in. Add a landing after 5 treads as space allows.

| Metric | Value | |---|---:| | Risers | 15 | | Exact riser | 7.47 in | | Treads | 14 | | Total run | 147 in | | Stringer length | ~184 in |

Pro Tips & Best Practices

  • Include finish thickness (treads, flooring) in total rise to avoid last-step mismatch.
  • Keep riser heights within 1/4 in of each other for comfort and code.
  • Pre-cut stringer templates and dry-fit before cutting all.
  • Add handrails at the correct height and ensure baluster spacing meets code.
  • Use non-slip nosings or treads, especially outdoors.

Related Calculators

FAQ

Q: How do I size riser height and tread depth?

A: Divide total rise by the number of risers for riser height and use a comfortable tread depth so the run fits your space. Common guidelines: riser ~7 to 7.75 in, tread ~10 to 11 in.

Q: What is the 2R+T rule?

A: A comfort rule of thumb: 2 x riser height + tread depth ~ 24-25 inches.

Q: How many steps do I need?

A: Steps (risers) = ceil(total rise / target riser height). Recompute exact riser height = total rise / steps.

Q: What headroom do I need?

A: Typical minimum headroom is about 6 ft 8 in (verify local code).

Q: Do I need landings or winders?

A: Long runs or turns require landings or winders; check code for minimum landing size and handrail rules.

Engineering note: Example dimensions use imperial units; convert to metric as needed. Always verify local building codes and safety requirements.

Call to Action

Enter total rise and your target riser/tread to get counts, run, and stringer lengths—tune the layout to meet comfort rules and code in minutes.