Question 1

How do I calculate the number of stairs I need?

Accepted Answer

Divide the total rise (height from lower floor to upper floor) by an ideal riser height of about 7 inches (178 mm), then round to the nearest whole number. That whole number is your count of risers. The calculator does this automatically and back-calculates the exact riser height.

Question 2

What is the ideal riser height and tread depth?

Accepted Answer

Most building codes target a riser between 6.5 and 7.75 inches (165-197 mm) with a tread depth of 10-11 inches (254-279 mm). The Blondel formula 2×riser + tread ≈ 25 inches (635 mm) gives a comfortable stride, which the calculator checks for you.

Question 3

What is the difference between a riser and a tread?

Accepted Answer

The riser is the vertical part of a step (its height), while the tread is the horizontal part you stand on (its depth). A typical residential staircase has 13-16 risers and one fewer tread than risers, because the top floor serves as the final step.

Question 4

How many stringers do I need for my stairs?

Accepted Answer

For stairs up to 36 inches wide you usually need three stringers (one at each end and one in the middle). Add a stringer for every additional 16-24 inches of width. The calculator reports the total stair run so you can buy stringer lumber of the right length.