# Stair Calculator

> Work out the number of steps, the exact riser height, total run, stair angle and stringer length from the floor-to-floor rise and your step sizes.

Category: Construction · Applies to: Worldwide · Last updated: 2026-10-29
Interactive calculator: https://calculators.geekmidst.com/calculators/stair-calculator

Divide the total rise by the tallest riser you will accept, round up to whole steps, and every riser becomes equal. The treads, run, pitch and stringer follow from that.

Also called: Stair stringer calculator, Stair rise and run calculator.

## Inputs
- Units (options: Millimetres, Inches; default mm)
- Total rise (finished floor to finished floor) (default 2700)
- Maximum riser height allowed (default 180)
- Tread depth (going), nosing excluded (default 270)

## Results
- Number of risers (steps)
- Each riser
- Number of treads
- Total run (horizontal length)
- Stair angle
- Stringer length along the slope (approx.)
- 2 × riser + going (comfort check)

## Formula

```
Risers = ⌈Total rise ÷ Max riser⌉;  Riser = Total rise ÷ Risers;  Treads = Risers − 1;  Run = Treads × Going;  Angle = arctan(Riser ÷ Going);  Stringer ≈ √(Rise² + Run²)
```

Where:
- Going: horizontal depth of each step, measured from nosing to nosing
- 2R + G: Blondel’s stride rule of thumb for comfortable stairs

## Worked example
1. 2,700 ÷ 180 = 15, so 15 risers of exactly 180 mm.
2. Treads = 15 − 1 = 14; run = 14 × 270 = 3,780 mm.
3. Angle = arctan(180 ÷ 270) = 33.7°; 2R + G = 2 × 180 + 270 = 630 mm.

**Result:** A 2,700 mm rise needs 15 risers of 180 mm and 14 treads of 270 mm, a 3.78 m run at 33.7°.

## What the result means

Every riser in a flight should be the same height, because people notice even small differences and trip. Stairs where 2R + G is roughly 600–650 mm (about 24–25.5 in) tend to feel natural; steeper or shallower stairs feel awkward.

## Assumptions and limits
- The top floor counts as the last step, so there is one tread fewer than risers.
- Nosings, landings and winders are not included.
- Maximum riser, minimum going, headroom, handrail and width rules come from your local building code; this calculator does not check them.
- The stringer length is the slope line only; add material for the cuts at top and bottom.

## Questions

### Why is there one fewer tread than risers?

The last “step” is the upper floor itself, so a flight with 15 risers has 14 treads.

### Should the total rise include floor finishes?

Yes. Measure between finished floor levels, including carpet, tile or boards, or the first and last steps will differ from the rest.

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_Quantities are estimates. Confirm requirements with your engineer or supplier before ordering materials._

Source: GM¹X CalcVerse — https://calculators.geekmidst.com/calculators/stair-calculator