ToolFeather

Stair Calculator

Plan a staircase from your total rise — get the number of steps, the exact riser height, the total run and the stringer length, with a note on code limits.

Stair Calculator

Total rise is the vertical distance from the lower floor to the upper floor. The tool picks a whole number of even risers close to your target.

A common building-code guide (IRC) is a maximum 7¾″ riser and a minimum 10″ tread — check your local code. 🔒 Calculated in your browser.

🔒 Nothing you enter is sent anywhere or stored. All processing happens in your browser.

Features

Even risers, every time

Enter the total rise and the tool divides it into a whole number of equal risers close to your target height — the key to a safe, comfortable stair.

Full step geometry

Get the riser height, number of treads, total run and the diagonal stringer length in one calculation.

Stringer length included

The stringer (the angled support board) is worked out with the Pythagorean theorem, so you know the board length to buy.

Code check built in

The result flags whether your riser and tread fall within the common 7¾″ / 10″ building-code guide.

How it works — in four simple steps

No signup, nothing to install — it all runs in your browser.

Step 01

Measure the total rise

Measure the vertical distance from the lower floor to the upper floor, in inches, and enter it.

Step 02

Set your targets

Enter a comfortable target riser height (around 7 inches) and your tread depth (10–11 inches is typical).

Step 03

Calculate

See the number of steps, exact riser height, total run and stringer length.

Step 04

Check the code note

Confirm the riser and tread are within your local building code before you build.

How it works

Designing a staircase starts from the total rise — the vertical distance from one finished floor to the next. You divide that rise into a whole number of equal risers (the vertical face of each step), because every step must be the same height for the stair to be safe and comfortable.

This calculator takes your total rise and a target riser height (7 inches is a comfortable default), finds the nearest whole number of even risers, and works out the exact riser height. From there it derives the number of treads (always one fewer than the risers), the total run (treads × tread depth), and the stringer length — the diagonal board that carries the steps, found with the Pythagorean theorem: √(rise² + run²).

It also flags whether your design falls within a common building-code guide — a maximum 7¾-inch riser and a minimum 10-inch tread (US IRC) — though you should always confirm your local code. Everything is calculated in your browser.

Examples

40″ total rise, 7″ target → 6 risers of 6.67″, 5 treads, 50″ run, 64″ stringer
108″ rise (9 ft), 7″ target → 15 risers of 7.2″, 14 treads, 140″ run

Frequently asked questions

How do you calculate stairs?
Divide the total rise by a comfortable riser height (about 7 inches) and round to a whole number of risers, then divide the total rise by that number for the exact riser height. Treads are one fewer than risers; total run is treads × tread depth. The calculator does all of this.
How is stringer length calculated?
The stringer is the diagonal, so it's the hypotenuse of a right triangle: stringer = √(total rise² + total run²). For a 40-inch rise and 50-inch run that's √(1600 + 2500) ≈ 64 inches.
What is a comfortable riser height?
Around 7 inches is comfortable for most people. Building codes (US IRC) commonly cap risers at 7¾ inches and require treads of at least 10 inches; the tool flags if you fall outside that.
Why is there one fewer tread than risers?
The top riser lands on the upper floor, which acts as the final step, so a staircase always has one more riser than it has treads.
Do I need to follow building code?
Yes — riser and tread limits exist for safety and vary by location. This tool uses a common US guide as a check, but always confirm your local building code before building.