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Stair calculator

Lay out equal stair risers and the required run

Enter the finished-floor rise and tread depth to calculate a straight flight, visualize its geometry, compare the available space, and review common residential stair criteria.

1 · Measure the stair space

Straight stair dimensions

Measure vertically from the lower finished floor to the upper finished floor. Tread depth is measured horizontally from nosing to nosing—not the loose board width.

Measurement display
Primary measurements
in
Measure straight up from the top of the lower finished floor to the top of the upper finished floor.
in
Horizontal distance between the foremost projections of adjacent treads.
in
Enter 0 to skip the space comparison. Do not include a landing in this measurement.
Clearances
in
in
Measure vertically above the sloped line connecting tread nosings and above landings.
Options
Which IRC edition applies to me?

Building-code adoption varies by state and local jurisdiction. Contact your local building department or permit office to confirm the adopted edition and amendments.

2 · Review the layout

Your stair result

Using 2021 IRC reference criteria. Your local jurisdiction may use a different edition or amendments.
Calculated layoutEqual risers147 11/16 in each
Treads
13
Total run
130 in
Stair angle
39.7°
Sloped line
169 in
Straight stair rise-and-run diagram14 equal risers at 7 11/16 in, 13 treads at 10 in, 130 in total run, and 39.7 degree stair angle.Total run: 130 inTotal rise: 108 in14 risers
14 equal risers at 7 11/16 in, 13 treads at 10 in, 130 in total run, and 39.7 degree stair angle. Diagram is proportional; construction and connection details are not shown.

Layout measurements

Total rise
108 in
Riser count
14
Actual riser height
7 11/16 in
Tread count
13
Tread depth
10 in
Total run
130 in
Sloped stringer line
169 in
Stair angle
39.7°

Reference review

ItemComparison
Riser height7.714 in calculated; 7.75 in reference maximum
Tread depth10.00 in entered; 10 in reference minimum
Clear width36.00 in entered; 36 in general reference minimum
Headroom80.00 in entered; 80 in reference minimum
Single-flight rise108.00 in entered; 151 in reference maximum between landings
Available run20.00 in remains

Calculation basis

2021 IRC, IRC R311.7 reference criteria for straight residential stairs.

risers = ceiling(total rise ÷ maximum riser)
actual riser = total rise ÷ riser count
treads = risers − 1
total run = tread count × tread depth
sloped line = √(total rise² + total run²)
  • A handrail is generally required because this layout has 14 risers.
  • Top and bottom landing, door-swing, guard, illumination, and walking-surface requirements still need project-specific review.
  • The sloped length is geometry only. It does not size stringers or include top/bottom connection cuts, tread-thickness adjustment, bearing, species, grade, loads, or fasteners.
  • All risers and treads within a flight must remain uniform; field layout and finish materials can change the first or last riser.
Measure Plan BuildGenerated https://measureplanbuild.com/calculators/stairs

Planning geometry only. Verify all dimensions, structural design, connections, safety features, permits, and current local requirements.

What this stair calculator covers

This tool models one straight flight between two finished floor levels. It divides the total rise into equal risers, uses one fewer tread than risers, and calculates the horizontal run, stair angle, and diagonal line through the flight.

Planning scope: The diagonal result is not a stringer-size recommendation or a cut length. Stair framing and fall protection are safety-critical and often require permits and inspection.

How to measure for stairs

  1. Measure vertically from the lower finished floor to the upper finished floor.
  2. Choose a nosing-to-nosing tread depth, not merely a tread-board width.
  3. Measure the unobstructed horizontal space available before any landing.
  4. Measure clear stair width and the lowest vertical headroom above the nosing line.
  5. Confirm the adopted code edition and amendments with the permit office.
  6. Review the full layout after finish-floor and tread materials are known.

Residential stair reference criteria

The versioned reference sets use the model IRC values for a 7 3/4-inch maximum riser, 10-inch minimum tread depth, 36-inch general clear width, 6-foot-8-inch minimum headroom, and 12-foot-7-inch maximum rise between floor levels or landings. The 2024 IRC reorganizes these provisions under Section R318.7; earlier editions use R311.7.

These comparisons do not cover every stair provision. Nosing, landings, doors, handrails, guards, openings, illumination, walking-surface slope, exterior exposure, accessibility, and structural details need separate review.

Worked example

A 108-inch finished-floor rise requires 14 equal risers under a 7 3/4-inch reference maximum. Each calculated rise is about 7.714 inches. With 13 treads at 10 inches, the straight flight uses 130 inches of horizontal run and has an angle of about 39.7 degrees.

Frequently asked questions

How many stair risers do I need?

Divide the finished-floor rise into equal risers without exceeding the selected reference maximum. The calculator rounds the count up, then divides the full rise equally.

Why is there one fewer tread than risers?

For a straight flight between finished floors, the upper floor acts as the final walking surface. Fourteen rises therefore normally have thirteen stair treads.

What is tread depth?

Tread depth is the horizontal distance between the foremost projections of adjacent treads, measured nosing to nosing. It is not automatically the same as the physical tread-board depth.

Does the sloped length tell me what stringer to buy?

No. It is only the geometric line between floor levels. Stringer material, cuts, bearing, connections, species, grade, loads, and permitted construction require separate design and local review.

Does an IRC reference mean my stairs meet local code?

No. Jurisdictions adopt different editions and amendments, and a complete review includes many requirements this geometry tool cannot evaluate.

Continue planning

Return to all DIY calculators to plan related deck, joist, roof, and material measurements.

Code and safety disclaimer

This calculator provides planning geometry and limited model-code comparisons, not engineering, a permit determination, a complete code review, or construction approval. Verify every measurement and requirement with qualified professionals and the authority having jurisdiction. Review the full measurement disclaimer.