Staircase Dimensions and Designs - What are the Calculations You Need?

Staircase Dimensions and Designs - What are the Calculations You Need?

It may seem like an obvious question with a simple solution, but there are some fundamental calculations that need to be taken into account when considering staircase dimensions and designs.

Renowned architect François Blondel developed a formula that enables you to calculate the optimal dimensions of a staircase, to ensure it is both efficient and comfortable. Whilst the necessary space to optimise a staircase may not always be available - space is often at a premium, particularly in newer properties - the successful application of Blondel’s formula relies on being as close as possible to the optimal dimensions. 

A staircase consists of a series of steps, formed by a tread (the horizontal section where the foot rests) and the riser (the vertical section). Each step also has one or more landings, handrails and a small nosing, which protrudes from the tread, increasing its size of the step without adding to the overall dimensions of the staircase.

The following is a sample calculation of a  2.60 metres high staircase:
1. Calculate the number of steps that will be needed

With an ideal riser of 18 cm, the height of the space is divided by the height of each step. The result should always be rounded up:

260/18 = 14.44 = 15 steps

2. Calculate the height of each riser
The height of the space is divided by the number of steps that we have just obtained:

260/15 = 17.33 cm height for each riser

3. Calculate the width of the tread
Apply the Blondel formula:

(2 x 17.33 cm) + (1 x tread) = 64 

Each tread will measure 29.34 cm
* The resulting staircase will have 15 steps of 29.34 cm of tread and 17.33 cm of riser

Whilst these calculations can be used as an approximate guide, the specific requirements of the project, as well as any local regulations, should always be taken into consideration.

What is the ideal stair width?
A minimum stair width of 80 cm is recommended for stairs in single-family homes, and greater than 1 metre in public buildings, though this is determined by use and regulatory requirements. A staircase within a busy public building, for example, may require a significantly larger stair width. 

As an approximate guide, two people could go up and down a 1.25 metre staircase simultaneously, and three people could go up and down a 1.85 metre staircase, with an approximate distance of 55 cm between the person and the handrail.

What is the optimal step number before a landing should be included?
The optimal number of steps to a landing is 15, after which a landing (ideally measuring at least 3 treads) should be included. 

What is the ideal ceiling height?
The height between the steps and the ceiling must be a minimum of 2.15 metres to comply with building regulations, with the handrail height varying between 80 and 90 cm from each step.

Should the tread and the riser remain consistent? 
Absolutely! The tread and the riser should remain consistent throughout the stair, to avoid causing imbalance to the user.