The floor-to-floor height is 2,750mm and the architect wants a stair that complies with AS 1657. You need the number of risers, actual riser height and total stair run before the builder frames the opening.
Stair Calculator
Stairs
Code: 115–190mm
Typically 240–355mm
Riser: 115–190mm · Going: 240–355mm · 2R + G = 550–700mm (comfort formula)
Results are estimates for planning purposes. Verify with current standards and a qualified professional.
1 What this calculator does
Calculates the number of risers, actual riser height, going (tread depth), total horizontal run and 2R+G check for a staircase. Verifies compliance with AS 1657 (Australian) or IBC (US) riser and going ranges. Supports millimetre and inch inputs.
2 Formula & professional reasoning
Number of risers = Round(Floor-to-floor height / Preferred riser)
Actual riser = Floor-to-floor height / Number of risers
Total run = (Number of risers - 1) x Going
2R+G check: 2 x Riser + Going (should be 550-700mm for comfort)
AS 1657 limits: Riser 115-190mm | Going 240-355mm
Risers are always equal -- every riser must be identical to prevent trip hazards. The number of risers is rounded to give an actual riser height as close as possible to the preferred height (typically 175mm) while dividing evenly into the floor-to-floor height. The 2R+G formula is the universal ergonomic check: sum of twice the riser plus the going should fall between 550mm and 700mm for comfortable stair geometry. Australian Standard AS 1657 sets the code limits.
3 Worked examples
⚠️ Illustrative example only — not clinical or professional instruction.
Basic
Residential stair -- 2,750mm floor-to-floor
Given: Floor height: 2,750mm | Preferred riser: 175mm | Going: 280mm
Working:
Risers: round(2750/175) = round(15.71) = 16 | Actual riser: 2750/16 = 171.9mm | Total run: (16-1) x 280 = 4,200mm | 2R+G: 2x171.9+280Answer: 16 risers at 171.9mm | Total run: 4.2m | 2R+G = 623.8mm -- comfortable
💡 2R+G of 624mm sits nicely within the 550-700mm comfort range. 16 risers is standard for a 2.75m residential floor height.
Standard
Commercial stair -- steeper preferred riser
Given: Floor height: 3,200mm | Preferred riser: 165mm | Going: 300mm
Working:
Risers: round(3200/165) = round(19.4) = 19 | Actual riser: 3200/19 = 168.4mm | Total run: (19-1) x 300 = 5,400mm | 2R+G: 2x168.4+300Answer: 19 risers at 168.4mm | Total run: 5.4m | 2R+G = 636.8mm
💡 5.4m total run requires significant floor space -- check that landing configuration fits within the building footprint.
Advanced
Tight stair -- checking minimum riser count
Given: Floor height: 2,400mm | Preferred riser: 190mm (maximum code limit) | Going: 240mm (minimum)
Working:
Risers: round(2400/190) = round(12.6) = 13 | Actual riser: 2400/13 = 184.6mm | 2R+G: 2x184.6+240 = 609.2mmAnswer: 13 risers at 184.6mm | Run: 2.88m | 2R+G = 609mm -- within range
💡 184.6mm is under 190mm maximum. 2R+G is 609mm -- comfortable. In tight spaces, maximum riser and minimum going can reduce the stair footprint significantly while staying code-compliant.
4 Sanity check
AS 1657 stair limits (Australia)
Riser: 115-190mm | Going: 240-355mm | 2R+G: 550-700mm | Maximum pitch: 45 degrees
IBC residential limits (US)
Riser: 152-216mm (4-7/8" minimum, 8-1/4" maximum) | Tread depth minimum: 279mm (11")
Comfort zones
Ideal riser: 165-175mm | Ideal going: 275-300mm | 2R+G of 600-640mm is optimal
All risers must be equal
Variation in riser height is a trip hazard and a building code violation
Always divide the total height evenly -- even if it means an actual riser slightly different from the preferred height.
5 Common errors
| Error | Cause | Consequence | Fix |
|---|---|---|---|
| Not checking that actual riser height falls within code limits | Rounding to a convenient number of risers without verifying the result | Non-compliant stair -- fails inspection, must be rebuilt | After calculating the actual riser, verify it is between 115mm and 190mm (AS 1657) or 4" to 8-1/4" (IBC). If it falls outside, adjust to the next number of risers and recalculate. |
| Forgetting the stair structure needs an extra riser compared to the treads | Counting treads instead of risers | Stair one riser too short or too long | For a stair with N risers, there are N-1 treads. The first riser is from the floor to the first tread; the last riser is from the top tread to the upper floor level. Number of treads = number of risers minus 1. |
| Using the finished floor-to-floor height without checking where final finishes are accounted for | Measuring before floor coverings are installed | Riser heights wrong after tiles or carpet are installed -- first or last riser wrong height | Account for floor finishes on both the lower and upper floor. If lower floor gets 15mm tiles and upper floor gets 12mm carpet, the structural frame height must be adjusted by the difference. |
| Not allowing for the landing or trimmer opening in the floor | Only calculating the stair geometry without checking the building structure | Stair opening not framed correctly -- structural work required on completion | Calculate the total horizontal run first. Then confirm that the floor opening (trimmer position) is in the right location to match the top of the stair. |
6 Reference & regulatory links
🇦🇺 Australia
7 Professional workflow
Common tools used alongside this one: