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Stair calculator

Put in the floor-to-floor height and the going you want. Get the number of risers, each riser's height, the treads, the stringer length, and a check against the National Construction Code limits.

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The answer

Risers 15 risers
Each riser 180.0 mm
Treads (goings) 14 treads
Total going, the stair's run 3,500 mm
2R + G 610.0 mm
Angle 35.8 degrees
Stringer, line length 4,420 mm
Stringer stock length to buy 4,800 mm
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Three stairs, worked out

Risers = the total rise divided by 175 mm, rounded, with one more if that leaves a riser over 190 mm. Treads = risers minus one. Total going = going x treads. Stringer = the square root of total rise squared plus total going squared.

Each answer is checked against NCC 2022 Housing Provisions Table 11.2.2a, read 9 October 2026:

  • Riser 115 to 190 mm.
  • Going 240 to 355 mm.
  • 2R + G between 550 and 700 mm.
  • 2 to 18 risers in a flight.

A house stair

2,700 mm floor to floor, 250 mm going, 900 mm wide
Total rise, floor to floor 2700 mm
Going (tread depth, nosing to nosing) 250 mm
Stair width 900 mm
Each riser 180.0 mm
Treads (goings) 14 treads
Total going, the stair's run 3,500 mm
2R + G 610.0 mm
Angle 35.8 degrees
Stringer, line length 4,420 mm
Stringer stock length to buy 4,800 mm
Risers 15 risers

Steps off a deck

1,050 mm to the deck, 280 mm going, 1,200 mm wide
Total rise, floor to floor 1050 mm
Going (tread depth, nosing to nosing) 280 mm
Stair width 1200 mm
Each riser 175.0 mm
Treads (goings) 5 treads
Total going, the stair's run 1,400 mm
2R + G 630.0 mm
Angle 32.0 degrees
Stringer, line length 1,750 mm
Stringer stock length to buy 2,100 mm
Risers 6 risers

A going that fails

2,400 mm rise with a 220 mm going
Total rise, floor to floor 2400 mm
Going (tread depth, nosing to nosing) 220 mm
Stair width 900 mm
Each riser 171.4 mm
Treads (goings) 13 treads
Total going, the stair's run 2,860 mm
2R + G 562.8 mm
Angle 37.9 degrees
Stringer, line length 3,734 mm
Stringer stock length to buy 4,200 mm
Risers 14 risers

Tight on space is common; the fix is a longer run or a landing, not a shorter going.

A 220 mm going is outside the NCC's 240 to 355 mm.

This checks the riser, going and flight limits only. Handrails, balustrades, landings, headroom and open-riser gaps have their own NCC clauses, and the certifier has the final say.

Stair questions#

What are the NCC limits for stair risers and goings?
NCC 2022 Housing Provisions Table 11.2.2a: riser 115 to 190 mm, going 240 to 355 mm, 2R + G 550 to 700 mm, and 2 to 18 risers a flight, for stairs other than spiral stairs. Read 9 October 2026; check the edition your job is approved under.
How do I work out how many risers I need?
Divide the total rise, floor to floor, by a comfortable riser of about 175 mm and round to a whole number. Divide the total rise by that count to get the exact riser. 2,700 mm / 175 = 15.4, so 15 risers of 180 mm.
Why is there one less tread than risers?
The top step is the floor you arrive on. A flight of 15 risers has 14 treads.
What is 2R + G?
Two risers plus one going, the NCC's check that a stair is neither too steep nor too shallow for a normal stride. 2 x 180 + 250 = 610 mm, comfortably inside 550 to 700.
How long should the stringer be?
The line length is the square root of the total rise squared plus the total going squared. Buy longer for the plumb cut at the top and the level cut at the bottom: the calculator adds 300 mm and rounds up to the next 300 mm length.