Stair Tread & Riser Calculator

How to lay out comfortable stairs

1. Measure total rise from finished floor to finished floor (or landing). Include finished materials in your measurement.
2. Pick a target riser height in the comfort/code range (often 7"–7.75"). The calculator rounds risers to a whole count and recomputes exact height.
3. We apply 2R+T≈25 to propose tread depth, with a 10" minimum. Short treads cause toe-stubbing and code issues.
4. Add landings per code for tall runs or direction changes. Total run here is linear; adjust for winders or layouts with turns.

Check local code for max riser height variance (often ≤3/8" across a flight) and nosing requirements.

Quick stair layout tips

Stair design basics (field guide)

Comfortable stairs are predictable: every riser is the same height, every tread is the same depth, and the 2R+T≈24–25 rule keeps your stride consistent. This guide gives practical context for the calculator results so you can sanity-check a layout before you cut stringers or order materials.

1) Measure total rise correctly

Total rise is finished floor to finished floor (or landing to landing). Add the thickness of floor finishes—tile, hardwood, carpet, subfloor, and nosing trim. Missing even a 3/4" finish can throw riser consistency off and cause a trip hazard at the top or bottom step.

2) Choose a target riser height in the comfort/code band

Most residential codes cap risers around 7-3/4" and require tread depths around 10" minimum (check your jurisdiction). Many builders aim for 7"–7-1/2" risers and 10"–11" treads. The calculator rounds risers to a whole count, recomputes actual height, and then re-derives tread depth.

3) Apply the 2R+T rule thoughtfully

Blondel’s 2R+T ≈ 24–25 inches is a comfort heuristic, not a code substitute. If 2R+T yields a tread under 10", bump the tread up to meet code and revisit riser count if the run becomes too long for your space.

4) Plan for landings, headroom, and clear width

Long runs often need landings by code (e.g., after 12–16 risers) and must maintain headroom (commonly ≥6'8"). Total run from the calculator is linear; add landing length and turning space for L- or U-shaped stairs. Minimum clear width is also prescribed—don’t forget handrail projections.

5) Stringer layout and finish thickness

Lay out stringers with a framing square and stair gauges to keep cuts consistent. If treads or finish flooring add thickness, subtract it from the stringer layout so finished risers stay uniform. Test-fit with a scrap tread before cutting all stringers.

6) Nosing, overhangs, and anti-slip

Many codes require a nosing projection (e.g., 3/4" to 1-1/4") when tread depth is under a certain value. Add anti-slip nosing or tape for safety—especially on exterior stairs where rain or frost increases slip risk.

7) Guardrails and handrails

Handrails typically become mandatory after a small number of risers (often 3 or 4). Guards are required when the drop exceeds a certain height (commonly 30"). Plan blocking early so you can anchor rails securely without ugly retrofits.

8) Accessibility and ramps

If accessibility is a concern, consider a ramp (often 1:12 slope or gentler) or a platform lift. Mixing accessible routes with traditional stairs ensures inclusivity for all users.

Quick check: after calculating, verify riser variance (keep it tight), tread depth (meet or exceed code), headroom, and landing spacing. Re-run the calculator if finish materials change.