- Free stair calculator
- Rise, run & angle
- Dynamic stringer geometry
Stair Calculator
Use this stair calculator to calculate stair rise and run, number of risers, actual riser height, tread count, tread depth, total run, stair angle, and geometric stringer length. Enter a total rise, choose either a target riser height or an exact number of risers, and review the stair dimensions with a live side-view diagram.
Measure the total rise, divide it into a practical number of risers, choose the tread depth, then calculate total run, angle, and stringer length from the resulting geometry.
Stair Calculator
Calculate risers, actual riser height, treads, total run, stair angle, and stringer length with precise unit conversion and transparent geometry.
Vertical finished-floor-to-finished-floor height.
Use a target maximum riser height, or enter the exact number of risers.
Horizontal run of each tread used for geometry.
How to Use the Stair Calculator
This online stair calculator converts the main stair measurements into a complete straight-stair geometry estimate.
Measure the total rise
Measure vertically from the finished lower floor to the finished upper floor. Enter the value in inches, feet, centimeters, millimeters, or meters.
Choose the riser setup
Use a target or maximum riser height, or switch to exact riser count mode when you want to test a specific number of risers.
Enter tread depth
Add the horizontal tread depth used for the stair geometry. The calculator uses it to determine total run, angle, and stringer length.
Review dimensions and diagram
Check riser height, tread count, total run, stair angle, stringer length, the 2R + T value, and the dynamic stair diagram.
Stair Rise, Run, Riser, and Tread Formulas
The calculator applies straightforward geometry to the total rise, riser count, tread depth, and total run.
When target-riser mode is used, the calculator rounds the required riser count upward so the actual riser height does not exceed the target value.
- Risers = ceil(total rise ÷ target riser height)
- Actual riser height = total rise ÷ risers
- Treads = risers − 1 for the straight-stair assumption used here
Once total rise and total run are known, stair angle and geometric stringer length can be calculated from the right-triangle geometry.
- Angle = atan(total rise ÷ total run)
- Stringer = √(rise² + run²)
- Rise + run check = 2 × riser + tread
Stair Calculation Examples
These examples show how stair rise and run change with riser count and tread depth.
102 in total rise
Target riser: 7.5 in
Calculated risers: 14
Actual riser: 102 ÷ 14
14 risers with 10 in treads
Treads: 14 − 1 = 13
Total run: 13 × 10 in
102 in rise and 130 in run
Angle = atan(102 ÷ 130)
Stringer = √(102² + 130²)
Stair Rise and Run Calculator
Rise and run are the core measurements used to describe straight-stair geometry. Total rise is the full vertical height between finished floors. Total run is the combined horizontal distance of the treads. A stair rise and run calculator connects those measurements through the riser count and tread depth.
Stair Riser and Tread Calculator
The riser is the vertical height of each step, while tread depth is the horizontal run used for each tread in the geometry. The calculator can determine the actual riser height from a target maximum or from an exact number of risers. It then uses the tread depth to calculate the total horizontal run.
Stair stringer calculator
The calculator reports geometric stringer length from the total rise and total run using the Pythagorean theorem. This is the straight diagonal length of the stair geometry. Actual stringer layout and cutting details can depend on material, nosing, connections, landings, and construction requirements, so a dedicated stair stringer layout page can cover those details separately.
Stair angle, slope, and pitch
Stair angle is based on the relationship between total rise and total run. A steeper stair has more rise relative to run; a shallower stair has more horizontal run. This calculator reports the angle in degrees using the arctangent of total rise divided by total run.
How to measure stairs
Start with the finished-floor-to-finished-floor rise rather than a rough framing height if finished dimensions are available. Measure carefully, keep units consistent, and verify the resulting riser and tread dimensions against the requirements that apply to your project.
Stair Calculation Reference
These relationships summarize the main values produced by the stair dimensions calculator.
| Measurement | Formula | Meaning |
|---|---|---|
| Riser count | ceil(total rise ÷ target riser) | Whole number of risers in target-height mode |
| Actual riser height | Total rise ÷ risers | Vertical height per riser |
| Tread count | Risers − 1 | Straight-stair assumption used by this calculator |
| Total run | Treads × tread depth | Horizontal stair distance |
| Stair angle | atan(rise ÷ run) | Geometric stair slope in degrees |
| Stringer length | √(rise² + run²) | Straight diagonal geometry length |
Frequently Asked Questions
Quick answers about stair rise, run, risers, treads, stringer length, and stair angle.
How do you calculate stairs?
Measure the total rise, choose a target riser height or exact riser count, calculate the actual riser height, and use the tread depth to determine total run, stair angle, and stringer length.
How do you calculate stair rise and run?
Actual riser height equals total rise divided by the number of risers. For the straight-stair assumption used here, treads equal risers minus one, and total run equals tread depth multiplied by the number of treads.
How is stair stringer length calculated?
The geometric stringer length is √(total rise² + total run²). This represents the straight diagonal length of the stair triangle.
How is stair angle calculated?
Stair angle is the arctangent of total rise divided by total run, converted to degrees.
Can I enter an exact number of risers?
Yes. Switch from target riser height mode to exact number of risers, then enter the riser count you want to evaluate.
What is the 2R + T value?
It is a simple relationship calculated as two times the actual riser height plus the tread depth. The tool reports the value for planning reference; it does not determine code compliance.
Does this stair calculator check building codes?
No. The advanced fields can compare results with optional limits that you enter, but building-code requirements vary by location, occupancy, stair type, and project conditions.
Can I use this as a deck stair calculator?
The geometry may be useful for general reference, but deck stairs have project-specific layout and code considerations. A dedicated deck stair calculator is better suited to that search intent.
Useful Construction Calculators
Use related tools when you need area, volume, material, or lumber calculations alongside stair planning.