How to Correctly Calculate Riser Height for an Interior Staircase

Why getting riser height right matters

The riser height (the vertical distance between one tread and the next) is the single most important dimension in staircase design. Get it right and the ascent feels effortless and natural. Get it wrong and every climb is either a stretch or a shuffle - uncomfortable, tiring, and potentially dangerous.

The fundamental formula

The standard formula for staircase ergonomics is known as Blondel's Formula:

2R + T = 63 cm

Where:

• R = riser height (the vertical rise per step)
• T = tread depth (the horizontal run per step, from nosing to nosing)
• 63 cm = the average human stride

This formula ensures that the relationship between rise and run mirrors natural human gait - a staircase that feels instinctively comfortable.

Optimal dimensions

• Riser height (R): optimal range 17-19 cm. Maximum permitted under most building regulations: 22 cm.
• Tread depth (T): optimal range 25-30 cm. Minimum: 21 cm (as in compact models such as LUMIA and VELORA).
• Minimum headroom: 200 cm, measured vertically from the tread nosing to any overhead obstruction.

A complete worked example

Let us say your floor-to-floor height is 270 cm.

Step 1: Determine the number of risers

270 / 18 = 15 risers

If the result is not a whole number, round to the nearest whole number and recalculate: e.g. 275 / 16 = 17.2 cm per riser.

Step 2: Verify with Blondel's Formula

With R = 18 cm: T = 63 - (2 x 18) = 63 - 36 = 27 cm

A tread depth of 27 cm is ideal - comfortable and within standard dimensions.

Step 3: Calculate the floor plan footprint

For a straight flight: Number of treads = 15 - 1 = 14 treads
Total run = 14 x 27 cm = 378 cm ~ 3.78 metres

Adjusting for compact staircases

For space-saving models (SCALA, LUMIA, VELORA) with alternating or curved treads, the formula still applies - but the effective tread depth per step is reduced because alternating treads are accessed by alternate feet. This allows a shorter floor run for the same number of risers.

Example: SCALA and LUMIA have a tread depth of 210 mm (21 cm) per step. With a riser height of 19 cm:
2 x 19 + 21 = 59 cm (slightly below the 63 cm ideal, but acceptable for compact configurations).

Adjustable riser systems

Most SCALUX modular models (TORINO, MANHATTAN, LONDON, SCALA, LUMIA, VELORA) feature adjustable riser heights - typically 17-23 cm. This means the kit covers a range of floor heights without cutting or modification. You simply adjust the spacing between treads at installation.

Summary checklist

• Measure floor-to-floor height precisely (include both floor finishes).
• Choose a target riser height between 17 and 19 cm.
• Divide floor height by riser height to get number of risers (round and recalculate).
• Verify with Blondel's Formula: 2R + T = 63 cm.
• Check the resulting floor run fits within your available space.
• Confirm the model you are considering covers your floor height range.

Conclusion

Calculating riser height is simple once you know the formula. The most common mistake is measuring only the structural floor depth and forgetting to add the finished floor covering. Always measure to the finished floor surface - the surface you will actually walk on - both below and above the staircase.

If you are uncertain, our team at SCALUX is available for free technical consultation. We will help you calculate the correct dimensions for your specific situation.