Spiral staircases deservedly attract the attention of private landlords. This beautiful design will give any home the solidity and attractiveness. The technology of manufacture of spiral stairs is quite simple. Taking into account the availability of various building materials to make a ladder, anyone, who has some knowledge in joinery, can master it. The only subject of difficulty in creating this original element of the interior is determining the correct size of the spiral staircase in the production of drawings. In this article, we will explain how to calculate a spiral staircase for your home quickly and practically.

The main parameters of the ladders: counting steps

One of the first things for calculating helical stairs is the correct calculation of the sizes of steps of design. That’s why you need to focus on the legend of the parameters below:

  • H – the height of the structure. It is determined by the sum of the distance from the floor to ceiling beams about their thickness;
  • H1 – interturn distance;
  • h – the height of the steps;
  • h1 – tread;
  • R is the outer radius of the stage;
  • R1 – the radius point of the main line of descent-ascent.

These symbols will be used later in performing calculations and drawings. It must be remembered that the design of spiral staircases is not an independent activity. Their parameters such as diameter, width or the already mentioned dimensions of the steps must fit into the existing standards and rules. Compliance with all requirements, sizes of levels and other parameters will ensure the safety and durability of stair design. Therefore, the production of drawings of steps always takes into account the following points:

  1. The distance between the turns of the structure (H1) cannot be less than the average height of a person (or preferably not less than 2 m). Otherwise, the person using the ladder will unnaturally stoop to avoid hitting his head on a higher level.
  1. Ascent and descent always occur on conventional lines, attributable to 1/3 of the radius from the outer edge of the step. It  is where the tread should be equal to 20-30 cm, which will provide convenience for the foot.
  2. The width of the stage cannot be less than 10 cm in the area near the front.
  3. During making the drawings of a spiral staircase, you should be aware that its diameter is either equal or not less than 3 meters, or the design shall provide handrails with a height of 90-10 cm.
  4. If there is not a riser in the drawings, then according to the safety regulations the distance between each of the steps should be 12-22 inches.

Design nuances: how to calculate stairs

Calculation of spiral staircases is a procedure that requires perseverance. Only 100% correct computing will turn your idea into a beautiful and safe design. If you want to have an acceptable work on the project of a spiral staircase, it is desirable to make a preliminary scheme with its size and carry out all the calculations. Carrying out such kinds of work, special construction calculators will help you– programs that allow you to make calculations of the spiral staircase even online efficiently. They are easy to use, have intuitive interfaces and turn the project work into a real pleasure.

The program is not available online; you can buy a CD with such licensed software. This bargain will allow using a computer to create quality drawings of building designs based on specified parameters width, height, diameter, etc. indicators, which are entered in a particular window.

The calculation of the flight of stairs should start with calculating the area of the plot allocated for the arrangement of inter-floor construction. This critical resource is essential for the determination of the minimum diameter of spiral stairs, as well as further calculations of the structural dimensions.

After that, you should define the height of the interior element (N). You should measure the distance from the flooring of the first floor to the second one, given the thickness of the slab. It should be defined in terms of input/output, which will allow the drawing to determine the angle at which the stairway will be twisted.

After completing these preliminary measurements, calculate the number of steps. For example, let’s use a conditional calculation spiral staircase with a diameter of 2000 mm (radius — 1000 mm), a height of 3500 mm and a vertical angle of twist of 360 degrees. We get: R = 1000; N = 3500; ω =360°.

It is important to note that all measurements and calculations of parameters for drawings with the use of formulas are made exclusively in millimeters!

The algorithm of calculations is:

  1. Compute L — the length of the march at the lift line with the help of the formula 2π*R1, where R1 is equal to 2/3 of the outer radius of the steps since the main line of rising is 1/3 of the radius:

L =2π*R1 =4/3 NR = 4/3*3,14*1000 = mm. 4190, i.e., the full circumference between the floors is 4 m of 19 mm.

  1. Divide the resulting length by the depth of tread of step(h1), for example, 22 cm:

n (number of steps) = L / h1 = 4190/220 = 19,045

Rounding the result we obtain 19 steps, but given the fact that the top step will coincide with the floor of the top floor, we should deduct one step. So, we need 18 steps.


  1. Knowledge of the number of stages will help to determine their external and internal depth. It is necessary to divide the external or internal length of the circumferences of the stairs on the above number. Tread depth around the central support can be defined with 10 cm, and the external one is computed:

h1 EXT = is essential/n. Here is essential =2nr = 2*3,14*1000 = 6280 mm.

Thus we get:

h1 EXT = 6280/19 = 0,330 m = 330 mm is the tread depth on the outer edge.


  1. Determine the height of the riser (if any), dividing the height of the stair (N) into all the same stages:

h riser = 3500/19 = 184 mm.

Based on the fact that helical designs usually do not use risers, you can adjust the distance between the steps in the direction of increasing intervals. While adjustments, you should check the compliance of the obtained results to the reference size, according to which the double height of a step in the amount of its depth shall be within the range from 60 to 65 cm.

If you want to get precise calculations, we recommend you to view online training videos dedicated to this issue. Verification of the obtained results is carried out by any popular program for calculation of spiral stairs.

Calculate the diameter of the staircase and width of the staircase

At this stage, everything is quite simple. The diameter should always be slightly smaller than the size of the opening of a spiral staircase. The exception is the option when installing the balusters on the outer edge of the steps. In this case, the width of the stair opening may coincide with the diameter of the structure.
For example, the diameter is 220 cm, and we reduce it to 200 cm (220-20 = 200), considering only a part of the tread that is designed for walking. In this case, the length of the step is equal to the radius: 200/2 = 100 cm the width of a spiral staircase is 1/2 less than the thickness of the support beams.

The calculation of the width of the top platform is made by calculating the loss of height when moving up the steps. In the case of our stairs with a turn of the march on 360 degrees, the ascent for one step will decrease the distance to the ground by 22 cm. Going up to the 5th step, the loss of height will be about 110 cm. If we take into account the thickness of the slab (p = 20 cm), the stock remains more than 2 meters. Thus, the width of the top platform may be within the width of 5 steps. If you increase it to the 6th step, the six-foot margin will disappear, and your head will cling to the top of the structure.
The verification of the calculations is carried out with the following formula:

  • H1 = H-5h-p = 350-110-20 = 220 cm (a good result).

Substituting into this formula, we can calculate the most suitable size.
As you can see, the exact calculation of all parameters of spiral staircases for further fabrication drawings is painstaking work, but a simple and interesting one. Using these skills or with the help of online designer of stairs, you will be able to prepare a quality project and bring it to life.


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