Stair Calculator

Straight-flight geometry

Plan a straight stair flight

Enter each choice beside the dimension it controls. This geometry estimate does not check structure, headroom, guards, handrails, or local code.

Geometry model 1.2.0

Input dimensions

Four decisions, in order

The active value stays directly below the choice that controls it.

Units

Horizontal runEnter one tread run or the full flight run.

How will you enter the run?

One tread runEntire flight

Run of one step

Horizontal nose-to-nose spacing, not the full board depth.

Total riseMeasure finished lower floor to finished upper floor.

Finished-floor rise

This is the full vertical height of the stair flight.

Riser layoutUse a planning maximum or an exact riser count.

How will you set the risers?

Maximum riseExact count

Maximum rise of one step

Equal risers are calculated at or below this planning limit.

Mount type

Mount typeChoose how the flight meets the upper floor.

Standard mountUpper floor is the final walking surface.R risers · R − 1 tread runsFlush mountTop tread is level with the upper floor.R risers · R tread runs

Enter the flight dimensions, then calculate to replace the guide labels with your values and open the result summary.

Worked starting points

Try a complete example

Simple four-riser check

28 in rise · 7 in maximum · 10 in tread

Typical straight flight

105 in rise · 7.5 in maximum · 10 in tread

Metric flush-mount layout

280 cm rise · 16 risers · 400 cm total run

Straight-flight geometry audit

Resolve risers, tread runs, pitch, and the upper connection coherently

A straight stair must divide one measured floor-to-floor rise into equal risers while fitting a planned horizontal run. Compare a standard upper-floor connection with a flush top tread, and solve from either a planning maximum or a fixed count. This calculator tests geometry; it does not establish the locally legal stair, size a stringer, design a guard, or replace field verification.

Step-by-step guide · Straight-flight geometry audit

Let integer riser count control the recalculation

Worked division: 105 in ÷ 14 = 7.5 in equal risers
Standard-mount run: 13 tread runs × 10 in = 130 in
Pitch and line: 36.87° pitch · 162.5 in idealized line

Choose a candidate count
Divide total rise by the permitted candidate riser, then round upward to a whole number. Re-divide the unchanged total rise by that integer; never round a riser and multiply it back into a different total height.
Compute the walking run
Enter the horizontal nose-to-nose run of one tread, or enter the total available run and let the calculator divide it across the selected mount's run intervals. Do not substitute the physical depth of a board that includes a nosing overhang. Winders, landings, curved stairs, and detailed nosing geometry require additional definitions and are not represented by this straight-flight model.
Audit pitch and the selected mount line
Step pitch is the arctangent of one actual riser divided by one unit run. For a standard connection, the upper finished floor acts as the final walking surface, so the idealized stringer vertical is total rise minus one riser: 97.5 inches in the worked case. Its line is the hypotenuse of 97.5 inches by 130 inches, or 162.5 inches. A flush connection instead uses the full rise and its own total run. Neither line is notch geometry, a bearing detail, a strength check, a cut limit, or a connection design.

Resolve risers, tread runs, pitch, and the upper connection coherently: A straight stair must divide one measured floor-to-floor rise into equal risers while fitting a planned horizontal run. Compare a standard upper-floor connection with a flush top tread, and solve from either a planning maximum or a fixed count. This calculator tests geometry; it does not establish the locally legal stair, size a stringer, design a guard, or replace field verification.

Measure finished floor to finished floor

Total rise is the vertical difference between finished walking surfaces, not rough framing alone. Include the expected lower and upper finish build-ups before dividing it. With 105 inches of total rise and a selected maximum candidate riser of 7.5 inches, the quotient is exactly 14; therefore the flight uses fourteen equal 7.5 inch risers. A later flooring change would require recalculation because one short or tall end riser creates a trip hazard.

Write the available opening and landing positions beside the rise. In the standard connection used by the worked example, the upper finished floor is the final walking surface, so fourteen risers create thirteen horizontal tread runs. At a 10 inch nose-to-nose unit run, the total run is 130 inches. A flush connection adds a top tread at the upper elevation and therefore uses fourteen run intervals. Either result must fit the plan while preserving landings, headroom, door swings, circulation, and guard conditions outside the simple triangle.

Let integer riser count control the recalculation

Choose a candidate count
Divide total rise by the permitted candidate riser, then round upward to a whole number. Re-divide the unchanged total rise by that integer; never round a riser and multiply it back into a different total height.
Compute the walking run
Enter the horizontal nose-to-nose run of one tread, or enter the total available run and let the calculator divide it across the selected mount's run intervals. Do not substitute the physical depth of a board that includes a nosing overhang. Winders, landings, curved stairs, and detailed nosing geometry require additional definitions and are not represented by this straight-flight model.
Audit pitch and the selected mount line
Step pitch is the arctangent of one actual riser divided by one unit run. For a standard connection, the upper finished floor acts as the final walking surface, so the idealized stringer vertical is total rise minus one riser: 97.5 inches in the worked case. Its line is the hypotenuse of 97.5 inches by 130 inches, or 162.5 inches. A flush connection instead uses the full rise and its own total run. Neither line is notch geometry, a bearing detail, a strength check, a cut limit, or a connection design.

Do not combine rules written for different stair scopes

Residential model code

The 2024 IRC publishes residential stair dimensions and uniformity provisions, but a jurisdiction may still enforce an earlier or amended edition. Confirm the permit set and local official before treating any numeric limit as controlling.

Construction-site stairways

OSHA 29 CFR 1926.1052 governs occupational stairways used during construction and includes temporary-stair requirements. Its 30-to-50-degree provision should not be presented as the finished-home design rule.

Accessibility standards

The 2010 ADA Standards include stair criteria for facilities within federal accessibility scope. Applicability depends on facility and route; accessibility review does not disappear because a residential calculator returns equal risers.

Carry approved geometry into materials and adjacent work

Once a designer or official confirms the flight, prepare member and finish takeoffs. Treads, risers, stringers, landings, posts, rails, fasteners, and finish flooring need their own material specifications. Review solid-stock volume with the board-foot calculator, or quantify a poured stair separately with the concrete shape calculator. Do not convert the idealized standard-mount line directly into a stock stringer order without accounting for bearing, cuts, member size, and the approved connection detail.

The ratio-and-angle arithmetic can be checked independently in the roof slope calculator, while an exterior landing surface may use the deck board planner. Before construction, field-check the actual elevations and opening, then coordinate headroom, landing size, handrails, guards, lighting, fire separation, and structural details under the locally adopted code and stamped plans. Equal arithmetic is necessary, but it is not complete stair design.

Important limitations

This is straight-flight geometry only. It does not approve local-code compliance, model nosing details or headroom, size or notch a stringer, check loads and connections, or design winders, spiral stairs, landings, guards, or handrails.

Review the stated scope, calculation method, assumptions, supported inputs, and effective dates, and obtain qualified advice before using a high-stakes result.

This formula passed its registered engineering tests and is published under an explicit site-owner policy authorization. No independent expert, QA, editorial, legal, or third-party review is claimed. Verify consequential results with a qualified professional.

This subject may affect health, finance, tax, legal, or other consequential decisions. It has not received an independent domain-expert review; consult a qualified professional before relying on it.

Straight-flight geometry audit

Resolve risers, tread runs, pitch, and the upper connection coherently

Step-by-step guide · Straight-flight geometry audit

Let integer riser count control the recalculation

Worked division: 105 in ÷ 14 = 7.5 in equal risers
Standard-mount run: 13 tread runs × 10 in = 130 in
Pitch and line: 36.87° pitch · 162.5 in idealized line

Choose a candidate count
Divide total rise by the permitted candidate riser, then round upward to a whole number. Re-divide the unchanged total rise by that integer; never round a riser and multiply it back into a different total height.
Compute the walking run
Enter the horizontal nose-to-nose run of one tread, or enter the total available run and let the calculator divide it across the selected mount's run intervals. Do not substitute the physical depth of a board that includes a nosing overhang. Winders, landings, curved stairs, and detailed nosing geometry require additional definitions and are not represented by this straight-flight model.
Audit pitch and the selected mount line
Step pitch is the arctangent of one actual riser divided by one unit run. For a standard connection, the upper finished floor acts as the final walking surface, so the idealized stringer vertical is total rise minus one riser: 97.5 inches in the worked case. Its line is the hypotenuse of 97.5 inches by 130 inches, or 162.5 inches. A flush connection instead uses the full rise and its own total run. Neither line is notch geometry, a bearing detail, a strength check, a cut limit, or a connection design.

Measure finished floor to finished floor

Let integer riser count control the recalculation

Choose a candidate count
Divide total rise by the permitted candidate riser, then round upward to a whole number. Re-divide the unchanged total rise by that integer; never round a riser and multiply it back into a different total height.
Compute the walking run
Enter the horizontal nose-to-nose run of one tread, or enter the total available run and let the calculator divide it across the selected mount's run intervals. Do not substitute the physical depth of a board that includes a nosing overhang. Winders, landings, curved stairs, and detailed nosing geometry require additional definitions and are not represented by this straight-flight model.
Audit pitch and the selected mount line
Step pitch is the arctangent of one actual riser divided by one unit run. For a standard connection, the upper finished floor acts as the final walking surface, so the idealized stringer vertical is total rise minus one riser: 97.5 inches in the worked case. Its line is the hypotenuse of 97.5 inches by 130 inches, or 162.5 inches. A flush connection instead uses the full rise and its own total run. Neither line is notch geometry, a bearing detail, a strength check, a cut limit, or a connection design.

Four decisions, in order

Simple four-riser check

Typical straight flight

Metric flush-mount layout

Choose a candidate count

Compute the walking run

Audit pitch and the selected mount line

Measure finished floor to finished floor

Let integer riser count control the recalculation

Do not combine rules written for different stair scopes

Residential model code

Construction-site stairways

Accessibility standards

Carry approved geometry into materials and adjacent work

Important limitations

Four decisions, in order

Simple four-riser check

Typical straight flight

Metric flush-mount layout

Choose a candidate count

Compute the walking run

Audit pitch and the selected mount line

Measure finished floor to finished floor

Let integer riser count control the recalculation

Do not combine rules written for different stair scopes

Residential model code

Construction-site stairways

Accessibility standards

Carry approved geometry into materials and adjacent work