Calculate stair risers, tread count, tread depth, total run, stair angle and stringer length from your floor height and stair dimensions.
Calculate Your Stairs
Stair Calculation Results
How the Stair Calculator Works
The calculator starts with the total vertical height between the two finished floors. It divides this height by the target riser height and rounds up to determine a whole number of risers.
The total rise is then divided evenly across those risers. This gives the actual riser height, which is often more useful than simply using the target value.
Actual Riser = Total Rise ÷ Number of Risers
Number of Treads = Number of Risers − 1
Total Run = Number of Treads × Tread Depth
Stringer Length = √(Total Rise² + Total Run²)
Stair Angle = arctan(Total Rise ÷ Total Run)
Riser and Tread Dimensions
Riser height controls how much you climb with each step. Tread depth controls the horizontal space available for each foot. A balanced relationship between the two helps create stairs that are practical to use.
The calculator also provides a 2R + T value. This is a common stair proportion check, where R represents riser height and T represents tread depth.
| Riser Height | Tread Depth | 2R + T | General Result |
|---|---|---|---|
| 15 cm | 30 cm | 60 cm | Moderate proportions |
| 16 cm | 28 cm | 60 cm | Moderate proportions |
| 17 cm | 28 cm | 62 cm | Moderate proportions |
| 17.5 cm | 28 cm | 63 cm | Moderate proportions |
| 18 cm | 27 cm | 63 cm | Moderate proportions |
Stair Calculation Example
Suppose the finished floor-to-floor height is 280 cm and the target riser is 17.5 cm.
280 ÷ 17.5 gives 16 risers. The actual riser height is therefore 17.5 cm. With 16 risers, the calculator uses 15 treads for a typical straight stair arrangement.
If the tread depth is 28 cm, the total horizontal run is 420 cm. The calculator then uses the total rise and total run to determine the approximate stringer length and stair angle.
Staircase Measurement Tips
Measure Finished Floor to Finished Floor
Measure from the finished surface of the lower floor to the finished surface of the upper floor. Floor finishes affect the final stair dimensions.
Keep Units Consistent
Enter the total rise, target riser, tread depth, nosing and stair width using the same selected unit.
Account for Floor Thickness
When a staircase is being built before the final floor finishes are installed, account for the expected finished floor levels. Small height differences affect the final riser calculation.
Check Headroom and Landing Space
A stair calculation does not determine every dimension required for a complete staircase. Headroom, landings, handrails, guards, stair width and structural support also need to be checked.
Important Stair Design Note
Stair Calculator FAQs
How many steps do I need for my staircase?
Divide the total floor-to-floor height by the target riser height, then round up to a whole number of risers. The calculator divides the total height evenly across those risers.
How do I calculate stair riser height?
Divide the total floor-to-floor height by the number of risers. The resulting value is the actual riser height.
How many treads does a staircase need?
For a typical straight staircase that finishes at the upper floor, the number of treads is often one less than the number of risers. The exact arrangement depends on the stair design and landing configuration.
What is the formula for stair stringer length?
For a straight stair, the approximate stringer length is the square root of total rise squared plus total horizontal run squared.
What is the 2R + T stair formula?
The 2R + T formula adds twice the riser height to the tread depth. It provides a common proportional check for stair dimensions.
Does this calculator include stair nosing?
The calculator includes a nosing input for reference, but the total horizontal run is based on the tread depth. Nosing projection does not get added again to the horizontal run.
Can I use this calculator for a deck staircase?
Yes. The same basic rise, riser, tread and run calculations apply to many straight stair projects. Local requirements should still be checked before construction.
Can this calculator design a complete staircase?
No. It provides basic dimensional estimates. A complete staircase design also involves structural support, headroom, landings, handrails, guards, connections and applicable building requirements.