Formula
Risers = round(total rise ÷ preferred riser). Actual riser = total rise ÷ risers. Treads in a straight flight = max(0, risers − 1). Total run = treads × tread going + landing allowance. Comfort check = 2 × actual riser + tread going.
Trade & Construction
Stair Calculator
Estimate stair risers, tread going, total run and a 2R+G comfort check from floor height and preferred riser height.
Calculator
Working calculator
Live result16 risers · 15 treads · 3750 mm run175.0 mm actual riser · 2R+G comfort check 600 mm
Formula used
Risers = round(total rise ÷ preferred riser). Actual riser = total rise ÷ risers. Treads in a straight flight = max(0, risers − 1). Total run = treads × tread going + landing allowance. Comfort check = 2 × actual riser + tread going.
This is the method behind the answer, so the result can be checked rather than simply trusted.What-if check
Nearby riser counts
Changing the whole riser count by one can noticeably change the actual riser height and total run. Use this table before a stair set-out is treated as settled.
| Risers | Actual riser | Total run |
|---|---|---|
| 15 | 186.7 mm | 3500 mm |
| 16 · selected | 175.0 mm | 3750 mm |
| 17 | 164.7 mm | 4000 mm |
Visual proof
Rise ÷ risers, treads × going
The profile is a simplified set-out sketch: total rise is divided into equal risers, while tread going builds the horizontal run.
Printable calculation report
Result: 16 risers · 15 treads · 3750 mm run. Assumption: The calculator treats the stair as a simple straight flight for measurement planning.
- Total rise
- 2800
- Preferred riser
- 175
- Tread going
- 250
- Landing allowance
- 0
- Page/date context
- 2026-05-16 UTC page version
- Page URL
- https://calculationtime.com/calculators/stair-calculator
Worked example
Total rise 2,800 mm ÷ preferred riser 175 mm = 16 risers. Actual riser = 2,800 ÷ 16 = 175.0 mm. Treads = 16 − 1 = 15. With 250 mm going, total run = 15 × 250 = 3,750 mm. The comfort check is 2 × 175 + 250 = 600 mm.
Professional note
Master’s Tip: measure finished-floor to finished-floor after allowing for floor coverings. A few millimetres of tile, screed or timber can change the exact riser height, and stair risers should be consistent across the flight.
Regional and unit assumptions
Standard or basis: transparent millimetre set-out arithmetic plus the common 2R+G comfort rule of thumb. This is a planning calculator only; it does not certify compliance with any national or local building code.
Assumptions and limitations
- The calculator treats the stair as a simple straight flight for measurement planning.
- The number of risers is rounded to a whole number because partial risers are not usable in a built stair.
- A straight flight usually has one fewer tread/going than risers because the upper floor or landing acts as the final step surface.
- Inputs are millimetres. The comfort check shown is the common 2R+G rule of thumb, not a building-code approval.
- Building codes, maximum riser limits, minimum going, headroom, handrails, landings, nosings and local permits must be checked separately before construction.
Methodology & Accuracy
How this calculator is checked
CalculationTime pages are built around visible arithmetic: the formula, assumptions, worked example and practical limitations are shown so the result can be checked rather than simply trusted.
Formula used
Risers = round(total rise ÷ preferred riser). Actual riser = total rise ÷ risers. Treads in a straight flight = max(0, risers − 1). Total run = treads × tread going + landing allowance. Comfort check = 2 × actual riser + tread going.
Standard or basis
Standard or basis: transparent millimetre set-out arithmetic plus the common 2R+G comfort rule of thumb. This is a planning calculator only; it does not certify compliance with any national or local building code.
Where a calculator follows a named legal, trade or industry standard, that standard is cited visibly. Otherwise the page uses transparent general arithmetic and states its limits.Master's Tip
Master’s Tip: measure finished-floor to finished-floor after allowing for floor coverings. A few millimetres of tile, screed or timber can change the exact riser height, and stair risers should be consistent across the flight.
Related calculators
Questions
How do I calculate the number of stair risers?
Divide the total vertical rise by the preferred riser height, then round to a whole number of risers. Divide the total rise by that whole riser count to get the actual riser height.
Why are there usually fewer treads than risers?
In a straight stair, the upper floor or landing acts as the final walking surface, so the flight normally has one fewer tread going than the number of risers.
What does 2R+G mean for stairs?
2R+G means two riser heights plus one going depth. It is a common comfort rule of thumb used to sense-check stair proportions, not a substitute for local code requirements.
Can this stair calculator approve a staircase for building work?
No. It is a measurement and set-out calculator. Check local code rules, permits, headroom, handrails, landing requirements and professional advice before building.
What should I print from a stair calculation?
Print the total rise, riser count, actual riser height, tread going, total run, comfort check, date and notes so a builder, homeowner or teacher can review the set-out later.
Calculation note
Stair calculation turns a vertical height into repeated, buildable steps. The arithmetic is simple, but the result matters because small riser differences are easy to feel underfoot and built stairs are controlled by local safety rules.
A stair is a repeated measurement system
The useful first step is turning the finished floor-to-floor height into a whole number of equal risers. Equal risers are important because people expect a regular rhythm when climbing or descending.
Run is a set-out quantity, not just a comfort number
Once the riser count is known, the horizontal run follows from the number of treads and the chosen going. That run estimate helps with floor planning, quotes, landings and whether the stair can physically fit in the space.
Code checks belong outside the quick formula
Building rules can set limits for riser height, tread depth, headroom, handrails, landings and guarding. This page keeps the arithmetic visible while warning that local code approval is a separate requirement.
Sources and further readingOSHA: Stairways and LaddersUK Government: Approved Document K