Use the free Stair Calculator to estimate risers, treads, total run, stringer length, lumber allowances, and basic material cost.
Comfortable stairs depend on consistent geometry. Because stairs are life-safety construction, use calculator results only for early planning and verify the final layout against approved plans and the locally adopted code.
Measure total rise at finished elevations
Measure vertically from the lower finished floor to the upper finished floor. Include planned flooring, decking, landings, and tread thickness. Changes at either end can make the first or last step inconsistent.
Calculate equal riser heights
Divide the total rise by an allowable number of risers. Every finished riser should be equal within the permitted tolerance. A calculator can suggest a count, but the maximum riser height and measurement method come from local requirements.
Determine treads and total run
A typical straight stair has one fewer tread than risers because the upper floor acts as the final walking surface. Multiply tread depth by the tread count for a preliminary run. Nosing rules and landing details can affect the final geometry.
Check available space
Confirm total run, stair width, headroom, landings, doors, hallway clearance, and the path of travel. Turning stairs, winders, and landings require a more detailed layout than a single straight-run estimate.
Plan stringers and framing
Stringer size, spacing, remaining wood at notches, bearing, attachment, species, grade, and loads determine structural capacity. Manufactured stringers and engineered stairs must follow their approved instructions.
Include guards and handrails
Required handrails, guard height, baluster spacing, graspability, returns, lighting, and fastening are not included in the material estimate. Exterior stairs also need weather-resistant materials, drainage, and suitable footings.
Make a full-scale check
Before cutting lumber, draw the complete stair or test a full-size layout. Confirm finished dimensions at the top and bottom and have structural or code questions reviewed by the appropriate professional or local authority.
Worked straight-stair example
Assume the finished floor-to-floor rise is 105 inches. If the applicable maximum riser height were 7.75 inches, dividing 105 by 7.75 gives 13.55, so the preliminary layout needs 14 equal risers. The actual riser height becomes 105 divided by 14, or 7.5 inches. A conventional straight flight ending at the upper floor would have 13 treads.
Using a 10-inch tread depth produces a preliminary run of 130 inches. The simple diagonal between the total rise and run is about 167 inches, or 13 feet 11 inches, before allowances for bearing, cuts, landings, and connection details. This math checks whether the idea fits; it does not approve a stringer or replace a full-scale layout.
Pre-cut verification checklist
- Measure from finished lower floor to finished upper floor.
- Confirm the locally permitted riser height, tread depth, width, and variation tolerance.
- Check headroom, landings, doors, guards, handrails, and the full travel path.
- Verify stringer material, spacing, remaining wood at notches, bearing, and attachment.
- Include finished tread and flooring thickness at the top and bottom.
- Draw or test the entire flight at full scale before cutting all stringers.
What the calculator cannot approve
Stairs are life-safety construction. The tool does not evaluate loads, species and grade, notched-stringer capacity, winder geometry, guard fastening, exterior foundations, accessibility requirements, or permit details. Use approved plans and the rules adopted by the local authority.
Review notes
This guide was reviewed on September 20, 2026. The example demonstrates equal-riser arithmetic and basic right-triangle geometry only. Read how our calculators work for our formula, rounding, and update practices.
Continue planning this project
Stair geometry should be coordinated with deck surfaces, framing members, and the lumber purchase list.