Metalwork · Stairs
Steel stair calculator
A 2.72 m floor-to-floor rise with risers of 180 mm at most takes 16 risers of 170 mm and 15 treads with a 280 mm going: 2R + G = 620 mm, a 4200 mm run and two 5242 mm stringers. In 200 × 10 flat bar with 4 mm folded plate treads it weighs about 352.8 kg. Change the sizes, the stringer and the treads: the calculator draws the stair, checks the step and opens the cut list in the bar optimizer.
Cut list
| Profile or material | Piece | Size (mm) | Qty |
|---|
What the codes say
This page does not know the code where you build: pick the comfortable step and type the riser and the going your code asks for. As an example of what one code says, Spain's CTE DB SUA (SUA 1, section 4) asks, on a stair inside a dwelling, for risers of 20 cm at most and goings of 22 cm at least (4.1); on the other stairs, goings of 28 cm at least on straight flights, risers between 13 and 18.5 cm (17.5 cm at most in public areas or where there is no lift) and 54 cm ≤ 2R + G ≤ 70 cm (4.2.1), with at least 3 steps per flight (4.2.2). The Blondel rule, 2R + G between 600 and 640 mm, is the comfortable step of the handbooks, not a code. The open sides of a stair take a railing: the metal railing calculator counts its balusters. Check the code in your country.
How it is worked out
For the stair above: 2720 / 180 = 15.1, so 16 risers of 2720 / 16 = 170 mm and 15 treads. With a 280 mm going the run is 15 × 280 = 4200 mm, 2 × 170 + 280 = 620 mm, inside 600 to 640, and the pitch is atan(170 / 280) = 31.3°. Each stringer: 16 × √(280² + 170²) = 16 × 327.57 = 5241.1, cut at 5242 mm. The 200 × 10 flat bar is 2000 mm², 15.700 kg/m: 2 × 5.242 m = 10.48 m, 164.6 kg. A 4 mm folded plate tread is 280 + 2 × 40 = 360 mm developed, 1000 × 360 × 4 mm × 7850 kg/m³ = 11.30 kg; 15 treads, 169.6 kg. The 40 × 40 × 4 angle is 304 mm², 2.386 kg/m: 30 cleats of 260 mm, 7.80 m, 18.6 kg. In all, 352.8 kg. The sections are sharp-cornered, as in the metal weight calculator, and the folds are counted flat: a rolled section or a bent plate weighs a little less.
What this page does not do
- It does not check the strength. The stringer section, the treads and the fixings for the load the stair must take are for whoever signs the job.
- It is one straight flight. No landings, winders or headroom.
- It does not count base plates, anchors, welding, the railing or paint. The stringer length is taken on the pitch line: add what the end cuts need.
Questions people ask
- How many steps does a stair need?
- Divide the floor-to-floor rise by the largest riser you want and round up: 2720 mm at 180 mm at most gives 16 risers of 170 mm and 15 treads, because the top step is the upper floor.
- What is the Blondel rule for stairs?
- Twice the riser plus the going should land between 600 and 640 mm, the length of a comfortable step: a 170 mm riser with a 280 mm going gives 620 mm. It is a rule of thumb from the handbooks, not a code; check the code in your country.
- How long is a steel stair stringer?
- On the pitch line, floor to floor, the number of risers times √(going² + riser²): 16 × √(280² + 170²) = 5242 mm for the stair above, plus what the end cuts need.
- How much does a steel stair weigh?
- The stair above, with two 200 × 10 flat bar stringers and 15 folded plate treads 4 mm thick and 1 m wide, weighs about 352.8 kg in steel.