# Stair Calculator

URL: https://speedycalculator.com/calculators/construction/stairs/
Last updated: 2026-10-25

> The stair calculator works out the number of risers and treads, exact riser height, total run, stringer length, stair angle and number of stringers from the floor-to-floor rise, and checks the comfort rule.

## Inputs

- Total rise (floor to floor) (in, cm, mm, ft, m)
- Maximum riser height (in, cm, mm, ft, m)
- Tread depth (run) (in, cm, mm, ft, m)
- Stair width (in, cm, mm, ft, m)
- Maximum stringer spacing (in, cm, mm, ft, m)

## Results

- Risers
- Riser height
- Riser height (fraction)
- Treads
- Total run
- Stringer length
- Stair angle
- Comfort check 2R + T
- Stringers

## Formula

```
Risers = ceil(total rise ÷ maximum riser); riser height = rise ÷ risers
Treads = risers − 1; total run = treads × tread depth
Stringer = √(rise² + run²); angle = atan(rise ÷ run); comfort: 2R + T ≈ 24–25 in
```

## Explanation

Comfortable, code-compliant stairs balance riser height and tread depth. The U.S. International Residential Code allows risers up to 7¾ in and treads of at least 10 in, with no more than ⅜ in variation between steps. A classic comfort rule says twice the riser plus the tread should be about 24–25 in (600–640 mm).

### How to use the Stair Calculator

- **Total rise (floor to floor)**
- **Maximum riser height**
- **Tread depth (run)**
- **Stair width**
- **Maximum stringer spacing**

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Enter the total rise from finished floor to finished floor, the maximum riser height, the tread depth (run), the stair width and stringer spacing. The calculator rounds up the risers, recalculates the exact riser height and gives the run, stringer length, angle and stringers.

### Code limits

CodeMax riserMin treadIRC (US residential)7¾ in10 inIBC (US commercial)7 in11 inUK Part K (private stair)220 mm220 mm goingNBC Canada (dwellings)200 mm255 mm run

### Tips for an accurate estimate

- Take measurements at floor level and at the ceiling – walls and rooms are often slightly out of square.
- Use the manufacturer's coverage, spacing and installation data when it differs from the typical values here.
- Keep a little extra of every finish material for touch-ups and repairs later.
- Check local building codes and permits before structural, electrical, plumbing or gas work.

### Common mistakes to avoid

- Sizing heating or cooling equipment by area alone when insulation, windows and climate make a big difference.
- Buying too little paint, stain or flooring and ending up with mismatched batches.
- Overlooking the extra material for steps, railings, gables and trim.

### Inputs explained

FieldWhat to enterTotal rise (floor to floor)Units: in, cm, mm, ft, mMaximum riser heightUnits: in, cm, mm, ft, mTread depth (run)Units: in, cm, mm, ft, mStair widthUnits: in, cm, mm, ft, mMaximum stringer spacingUnits: in, cm, mm, ft, m

### What each result means

- **Risers** = ceil([Total rise (floor to floor)]÷[Maximum riser height] - 0.000001)
- **Riser height** = [Total rise (floor to floor)]÷[Risers]
- **Riser height (fraction)** = [Riser height]
- **Treads** = [Risers] - 1
- **Total run** = [Treads]×[Tread depth (run)]
- **Stringer length** = sqrt([Total rise (floor to floor)]^2 + [Total run]^2)
- **Stair angle** = deg(atan([Total rise (floor to floor)]÷[Total run]))
- **Comfort check 2R + T** = 2×[Riser height] + [Tread depth (run)]
- **Stringers** = ceil([Stair width]÷[Maximum stringer spacing] - 0.000001) + 1

## Worked example

Inputs — Total rise (floor to floor): 108 in; Maximum riser height: 7.75 in; Tread depth (run): 10 in; Stair width: 36 in; Maximum stringer spacing: 16 in.

Results — **Risers = 14**; Riser height = 7.714 in; Riser height (fraction) = 7 11/16; Treads = 13; Total run = 130 in; Stringer length = 169.01 in; Stair angle = 39.7 °; Comfort check 2R + T = 25.43 in; Stringers = 4.

## Key terms

- **Riser**: The vertical face of a step.
- **Tread**: The horizontal part you step on.
- **Stringer**: The inclined board that supports the treads and risers.

## FAQ

**How many steps for a 9 ft rise?**
108 in ÷ 7¾ in = 13.9, so 14 risers of 7.71 in and 13 treads.

**What is the code for stair risers and treads?**
IRC: risers ≤ 7¾ in, treads ≥ 10 in, headroom ≥ 6 ft 8 in, width ≥ 36 in.

**What is the ideal stair angle?**
30–37°; above about 42° stairs feel like a ladder.

**What formula does the Stair Calculator use?**
Risers = ceil(total rise ÷ maximum riser); riser height = rise ÷ risers.


## Sources

- [International Code Council – IRC R311.7 Stairways](https://codes.iccsafe.org/)