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Stair Stringer Calculator: Rise, Run, Risers & Treads

Turn a verified finished-floor-to-finished-floor rise into an auditable straight-stair geometry plan. Choose either a target maximum riser height or a known riser count, enter the horizontal tread depth, and optionally check whether the resulting flight fits an available horizontal run.

Maintained by Home Measure Lab Editorial TeamUpdated Method & corrections

Project measurements

Change the defaults to match your project and the product you plan to buy.

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in
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Project result

Straight-stair rise/run geometry

Check the solved riser count and equal riser height first, then review tread count, total run, flight angle and the geometric stringer line. Use the optional fit check only as a space-planning cross-check.

Planning estimate only. Verify product coverage, package size, supplier specifications and project requirements before purchasing.

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Budget scenario

Add your current local costs

Use a current supplier subtotal or reuse a priced calculator result, then add optional delivery, tax and contingency. Home Measure Lab does not fetch or guess live prices.

This calculator does not currently expose a priced result. Enter a current supplier subtotal manually.
Material subtotal$0.00
Delivery / fees$0.00
Tax$0.00
Contingency$0.00
Planning total$0.00

Enter a current supplier subtotal or reuse a priced calculator result.

Budget values are local planning inputs, not live quotes. Verify tax treatment, delivery, labor and supplier pricing before purchasing.

Methodology

Formula, code boundary & assumptions

Riser count — target mode

ceil(total rise ÷ target maximum riser)

Ceiling keeps the solved equal riser no greater than the target you entered.

Actual equal riser

total rise ÷ riser count

A straight flight should not be laid out by using the target height for every step and leaving a different last riser.

Tread count

riser count − 1

For the simple model, the upper finished floor acts as the final walking surface.

Total horizontal run

tread count × entered tread depth

Tread depth is horizontal run per tread; nosing projection and local definitions remain separate.

Geometric stringer line

√(total rise² + total run²)

This is the overall stair-triangle hypotenuse, not a board cut list or structural stringer length.

How to measure this project

Measure the total vertical rise from the finished lower walking surface to the finished upper walking surface. Record the intended tread run horizontally, not along the stair slope. If finish thickness is not installed yet, work from the project detail and account for the finished elevations before laying out physical risers. Use the optional available-run input only when the horizontal clear planning distance is known from a reliable layout or drawing.

Before you buy materials

Do not buy or cut stringer stock from the geometric hypotenuse alone. Stringer board size, number of stringers, notches, bearing, landing attachment, hanger/hardware, tread/nosing detail and allowable spans depend on the actual assembly and applicable requirements. Verify the adopted local residential/building code and project documents before construction.

Reference

What each stair number means

QuantityDimensionUse
Total riseverticalfixed finished-surface height to overcome
Actual riservertical per stepequal division of total rise
Tread depthhorizontal per treadentered walking/run geometry
Total runhorizontalfootprint of the tread sequence
Stringer linesloped lengthoverall triangle cross-check only

Source evidence

Primary references behind key assumptions

These references document specific assumptions used or discussed on this page. The exact product label, technical data sheet, project drawings and applicable requirements take priority.

International Code Council — 2021 IRC R311.7.5 Stair Treads and Risers

Supports: The cited 2021 IRC provisions state residential stair tread/riser dimensional limits and uniformity rules within their defined scope, including a 7 3/4 inch maximum riser and 10 inch minimum tread depth.

Boundary: Model-code text is reference evidence only. Local adoption, amendments, stair type and the complete code/project requirements must be verified; HomeMeasureLab does not certify compliance.

OSHA — Fall Protection in Residential Construction

Supports: Residential roof work, including installing ridge poles and rafters, presents fall hazards and requires appropriate fall protection planning.

Boundary: This source supports the safety boundary only; it does not provide or validate HomeMeasureLab rafter geometry, lumber sizing or structural design.

Questions

Frequently asked questions

Why does the actual riser differ from my target?

The flight needs a whole number of equal risers. In target mode the calculator rounds the riser count upward, then divides total rise evenly across that count.

Is tread count always one less than riser count?

For the calculator’s simple straight flight where the upper floor is the last walking surface, yes. Landings, split flights and unusual conditions need separate modeling.

Does stringer length include the bottom or top cut details?

No. The reported value is the hypotenuse of the overall stair rise/run triangle. Bearing and attachment details can change the stock and mark-out requirements.

Does this calculator certify IRC compliance?

No. It exposes the geometry and lets you enter your own planning target. Verify the locally adopted code, amendments and complete stair requirements for the actual project.

Can I use this for winders, spiral stairs or multi-flight stairs?

No. Calculate a simple straight flight only; turns, winders, intermediate landings and multi-flight geometry require a different layout.

Next step

Keep this project moving

Follow the measurement into the most useful related reference, calculator or project view.

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Planning guides

Understand the inputs behind this calculator

All guides →

Interior

How to Measure Total Rise for Stairs

Measure finished-floor-to-finished-floor total rise for straight-stair planning and avoid finish-thickness, landing and sloped-measurement errors.

Read guide →

Interior

Stair Riser, Tread, Run & Stringer Geometry Explained

Understand stair risers, treads, total rise/run, angle and stringer-line geometry without confusing planning math with structural or code approval.

Read guide →

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