Wood & Trim

Stair Calculator

Compare a straight-flight riser count, actual rise and horizontal run.

Units

Your measurements

Results update as you type.

Example shown — use your own measurements.

Horizontal advance, excluding nosing overlap; enter your project’s chosen value.

Fractions and number formats

Use decimals (12.5), fractions (12 1/2 or 12-1/2), or explicit lengths (12ft 6in, 12′ 6″, 25 mm). A comma followed by one or two digits is a decimal comma: 12,5 = 12.5. Grouped commas mean thousands: 1,200 = 1200. Use a decimal point for ambiguous values. Scientific notation is not accepted.

Enter your measurements

Results update as you type.

About this calculator

Compare a straight-flight riser count, actual rise and horizontal run. Enter the measurements for the selected mode and compare the worked example below. The result describes geometry only.

How to measure

  • Measure the actual usable surface or internal space, using the field labels for the selected mode.
  • Keep openings and excluded areas separate so they are subtracted once.
  • Recheck units and label coverage before ordering.

How to use this calculator

  1. Enter the total floor-to-floor rise.
  2. Choose a target maximum riser height or an explicit whole riser count.
  3. Enter the horizontal going per tread from the project design.
  4. Compare actual riser height, tread count and run. The upper floor is the final landing; the diagonal is not a cut stringer length.

Formula

Target mode: risers = ceiling(total rise / target maximum rise)

Actual riser height = total rise / risers; treads = risers − 1

Run = treads × going; geometric slope = √(rise² + run²)

Assumptions

  • The flight is straight and has equal riser heights.
  • The upper floor is the final landing, so the model counts one fewer tread than risers.
  • Target height and going are user-supplied geometry inputs, not building-code recommendations.

Common mistakes

  • Applying the same allowance in both measurements and the extra-material field.
  • Entering coverage or yield from a different product or measurement basis.
  • Treating a quantity estimate as an installation or structural approval.

Worked example

Try it: press “Load example” above the form.

A 105 in total rise divided into 15 risers gives 7 in per riser. With the upper floor as landing, 14 goings of 10 in give 140 in run.

Limitations

Geometry only; no code compliance or construction approval. Upper floor is the final landing. The diagonal is not a cut stringer length. Headroom, landings, nosings, guards, accessibility, loads and permitted riser/tread dimensions need a separate design.

Frequently asked questions

Why are there fewer treads than risers?

This straight-flight model treats the upper floor as the final landing. A flight with 15 risers therefore has 14 treads. Different landing or stair configurations require a different geometric plan.

What does the worked example show?

A 105 in total rise divided into 15 risers gives 7 in per riser. With the upper floor as landing, 14 goings of 10 in give 140 in run.

Does the target riser height establish code compliance?

No. The entered target and going are comparison inputs. A project design must separately satisfy the applicable riser, tread, headroom, landing, guard and other requirements.

What needs a separate stair design check?

Geometry only; no code compliance or construction approval. Upper floor is the final landing. The diagonal is not a cut stringer length. Headroom, landings, nosings, guards, accessibility, loads and permitted riser/tread dimensions need a separate design.

Reviewed by Codex AI editorial agent (Editorial, 2026-11-12).

Sources

Sources explain the methods and any named product presets. Check your product label where coverage, yield or density differs.

  • NIST: Revised Unit Conversion Factors
  • Defined geometric and purchase-quantity model

    Formulae on this page define the arithmetic model. Worked examples are illustrative, not product or installation recommendations.

Calculation documentation · Updated 2026-11-11 · Version 1.6.4. Estimates are planning aids. Confirm quantities, coverage and prices with your supplier before purchasing. Found an error? Report it.

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