Stair Calculator
This stair calculator finds the number of steps, the riser height, the tread depth, the angle, and the stringer length from the total rise and run. Enter the rise, run, and a target riser and the stair calculator returns a full layout. As a stair stringer calculator it gives the numbers you need to cut the stringers.
Results
The Stair Calculator is part of our Structural collection. Browse more structural to size, convert, and check your work alongside this tool.
What the stair calculator shows
A safe, comfortable stair depends on splitting the total rise into even risers and matching them with a good tread depth. This stair calculator does the whole layout: the number of risers, the exact riser height, the tread depth, the stair angle, and the stringer length. As a stair stringer calculator it gives the diagonal length you cut the stringers to.
How the stair stringer calculator works
The stair stringer calculator divides the rise into even risers, then fits the treads and finds the stringer:
The stringer length is the diagonal, √(rise² + run²), and the angle is the slope of that line. There is always one fewer tread than riser, since the top riser lands on the upper floor.
Stair calculator example
A 2800 mm total rise, 3600 mm run, and a 180 mm target riser. The stair calculator gives:
So 16 risers of 175 mm and 15 treads of 240 mm, on a 4.56 m stringer. Change the rise and the stair calculator updates the layout at once.
How to use the stair calculator
Enter the total rise from finished floor to finished floor, the total run available, and a target riser height, then the stair calculator returns the layout. It rounds the risers to a whole number near your target, then works out the exact riser and tread. An online staircase calculator like this keeps the risers even, which is what makes a stair feel right and pass code.
Reading the stair calculator result
The riser height and tread depth are the comfort numbers: risers around 175 to 190 mm and treads around 240 to 280 mm feel right and meet most codes. The angle should sit near 30 to 37 degrees for a normal stair. The stringer length is what you mark and cut. Always check your local building code for the allowed riser and tread limits, since they vary, and keep every riser equal, which the stair calculator does for you.
When to use the stair calculator
- Laying out an indoor flight with the stair calculator
- Cutting stringers with the stair stringer calculator
- Planning deck steps with a deck stairs calculator
- Setting rise and run with a rise and run for stairs calculator
Common stair calculator mistakes
- Unequal risers. Every riser must be equal, or the stair is a trip hazard; the stair calculator enforces this.
- Measuring rough, not finished. Use finished floor to finished floor for the total rise.
- Ignoring code. Riser and tread limits vary by region, so check your local building code.
Tips for building stairs
- Keep the riser plus tread near 430 to 450 mm for comfort.
- Cut one stringer, test it, then copy it.
- Confirm riser and tread against your local code.
Calculate stringer for steps
To calculate a stringer for steps you treat the whole flight as a right triangle: the total rise is one side, the total run is the other, and the stringer is the hypotenuse, √(rise² + run²). Calculating stringers for stairs then means marking that diagonal board with the riser and tread of each step, usually with a framing square set to the riser and tread the stair calculator found. A deck stringer calculator works the same way outdoors, where the rise is from the ground to the deck. Cut one stringer carefully, check it in place, then use it as the template for the rest so every step matches.
Deck stairs calculator and stair angle
A deck stairs calculator and an indoor staircase calculator use the same math, but decks often have more freedom in the run, which lets you pick a gentler angle. The stair angle calculator part of the result is the slope of the stringer, and it follows straight from the riser and tread: a taller riser or a shorter tread makes the stair steeper. Aim for 30 to 37 degrees for a comfortable climb; much steeper feels like a ladder and much shallower wastes floor space. Keeping the riser plus tread near 430 to 450 mm, a common comfort rule, keeps the angle in that sweet spot, which the rise and run for stairs calculator makes easy to hit.
Stair riser calculator reference
Comfortable riser and tread ranges, a quick guide alongside the stair riser calculator:
| Element | Comfortable range | Note |
|---|---|---|
| Riser height | 175 to 190 mm | Keep every riser equal |
| Tread depth | 240 to 280 mm | Wider is easier to climb |
| Stair angle | 30 to 37° | Steeper is harder and less safe |
| Riser + tread | about 430 to 450 mm | A common comfort rule |
Stair Calculator FAQ
How does the stair calculator find the risers?
It divides the total rise by your target riser and rounds to a whole number, then divides the rise by that count for the exact riser. The stair calculator keeps every riser equal.
How do I calculate a stringer for steps?
The stringer is the diagonal, the square root of rise squared plus run squared. A stair stringer calculator gives that length so you can mark and cut the board.
Why is there one fewer tread than riser?
The top riser lands on the upper floor, so it needs no tread. That is why a stair calculator shows treads equal to risers minus one.
What riser and tread are comfortable?
Risers around 175 to 190 mm and treads around 240 to 280 mm. Check your local code, since the allowed limits vary by region.