About this calculator
Lay out a straight flight: the number of risers, exact riser height, total run, angle and stringer length, checked against SANS 10400-M, the stairways part of the National Building Regulations.
How it’s calculated
Risers = ceil(total rise ÷ maximum riser). Exact riser = total rise ÷ risers. Treads = risers − 1. Run = treads × tread depth. Stringer ≈ √(rise² + (run + one tread)²).
SANS 10400-M: rise 200 mm max (4.2.5), going 250 mm min (4.2.6), 2R + G between 570 and 650 mm (4.2.8), width at least 750 mm and headroom at least 2.1 m from the pitch line (4.2.1), no more than 3 m of rise between landings (4.2.3), and risers and goings within 6 mm of each other in a flight (4.2.7). Timber stringers for stairs up to 1.2 m wide are at least 48 × 225 mm, grade 5 (4.5.1).
Worked example
With these inputs:
- Total rise (floor to floor)
- 2600 mm
- Maximum riser height
- 200 mm
- Tread depth (going)
- 250 mm
- Nosing overhang
- 20 mm
- Stair width
- 900 mm
the result is:
- Risers
- 13 risers @ 200 mm
- Total run (going)
- 3 m
- Stair angle
- 38.7°
- Stringer length (approx.)
- 4.16 m
- 2R + G
- 650 mm
Tips from the trade
- Measure the total rise to the finished floor at both ends, not to the subfloor.
- Treat this as a layout check. SANS 10400-M, your approved plans and the municipal building inspector have the final say.
- For stairs wider than 900 mm, add a middle stringer.
Common questions
How many steps for a 2.6 m rise?
2600 mm ÷ 200 mm = 13, so 13 risers of exactly 200 mm. With 250 mm goings, 2R + G = 650 mm, right at the top of the SANS 10400-M range of 570–650 mm. Fourteen risers of 186 mm (2R + G = 621 mm) give an easier stair.
Results are estimates for planning and pricing. Check quantities against your drawings, the manufacturer’s data and SANS 10400 (the National Building Regulations) and your local municipality before ordering.