Staircase Calculator - Riser & Tread Calculator

Free staircase calculator. Calculate stair dimensions including risers, treads, stringer length, and angle. Ensure building code compliance for safe.

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What the staircase calculator does and when to use it

Laying out a staircase means fitting a whole number of equal steps between two floors. This calculator takes the total rise (the vertical distance from finished floor to finished floor) and, optionally, the total run (the horizontal space available) and works out the number of risers, the exact riser height, the number of treads, the tread depth, the stringer length and the stair angle. It then checks the result against common US residential code limits for riser height, tread depth and width.

Use it during planning, before you cut stringers or order lumber, and when checking whether a design that looks fine on paper can fit the space you have. If you leave the run blank it suggests a tread depth from the comfort rule, so you can see how much floor space the stair will need. Always confirm the final layout with your local building code and inspector, because requirements vary by jurisdiction and stair type.

How the numbers are derived

  • Number of risers = total rise / 7.5 in, rounded to the nearest whole number (at least 1). The 7.5 in target is a comfortable riser height.
  • Riser height = total rise / number of risers, so every riser is identical.
  • Number of treads = risers − 1, because the upper floor acts as the last tread.
  • Tread depth = total run / treads. With no run entered, tread = 25 − 2 × riser (at least 9 in), from the rule that two risers plus one tread should be about 25 in.
  • Stringer length = √(rise² + run²), and angle = arctan(rise / run).

Code checks used: riser at most 7.75 in, tread at least 10 in, width at least 36 in, and an angle between 30 and 35 degrees as a comfort guide. Inputs in feet, metres or centimetres are converted to inches internally.

Worked example: 108 in rise, 130 in run

  • Risers: 108 / 7.5 = 14.4, rounded to 14 risers.
  • Riser height: 108 / 14 = 7.71 in, under the 7.75 in limit.
  • Treads: 14 − 1 = 13; tread depth = 130 / 13 = 10.00 in, exactly meeting the minimum.
  • Stringer: √(108² + 130²) = √28,564 = 169.01 in.
  • Angle: arctan(108 / 130) = 39.7 degrees.

The calculator marks riser and tread as passing but flags the 39.7 degree angle as outside the 30 to 35 degree comfort range. The 2R + T check gives 2 × 7.71 + 10 = 25.4 in, slightly above the 25 in target, so this is a somewhat steep stair. More run would help.

Common mistakes and how to interpret the result

  • Measuring to the wrong surfaces. Total rise must be from finished floor to finished floor, including flooring thickness on both levels.
  • Counting treads and risers alike. A straight flight has one fewer tread than risers.
  • Forgetting that a code pass is not a permit. Headroom, handrails, landings and winder rules are not checked, and local codes may be stricter.
  • Ignoring the angle. A stair can meet the minimum tread and maximum riser and still feel steep, so use the angle as a warning.

Frequently Asked Questions

What is the ideal riser height?
In the US the residential code allows up to 7.75 in, and many builders aim for about 7 to 7.5 in. This calculator targets 7.5 in and adjusts to an equal riser size for your total rise.
Why is there one fewer tread than riser?
The top step is the floor itself, so a flight of 14 risers needs only 13 treads. If a stair has a nosing or platform, count carefully when cutting.
What if I do not know the total run?
Leave it blank. The calculator will suggest a tread depth from the 2R + T rule and report the run the stairs would need.
Does the calculator support metric?
Yes. Choose meters or centimeters from the Units menu and the results are shown in the same unit, although the code thresholds are US inch values converted to that unit.

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