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Stair Calculator

Calculate the number of risers, treads, total run, and stringer length for any staircase.

Quick answer

14 risers at 6.86 in, 13 treads at 11 in, ~11.9 ft of total run.

Calculator

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How it works

Total rise ÷ Target riser height = Number of risers

The total rise is divided by your target riser height and rounded up to the nearest whole number. This ensures every riser is at or below your target height for comfortable, code-compliant stairs.

Total rise ÷ Number of risers = Actual riser height

The actual riser height is recalculated by distributing the total rise evenly across all risers, so every step is exactly the same height.

Stringer length = √(rise² + run²)

The stringer length is the diagonal distance from the bottom to the top of the stairs, calculated using the Pythagorean theorem. This tells you how long your stringer boards need to be.

Worked example

A staircase with 100 in total rise, 7.5 in target riser height, and 11 in tread depth:

100 ÷ 7.5 = 13.33 → 14 risers

100 ÷ 14 = 7.14 in per riser

14 − 1 = 13 treads

13 × 11 = 143 in total run

√(100² + 143²) = 174.5 in stringer

Build 14 risers, 13 treads, with ~14.54 ft stringers.

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Stairs are the most code-regulated thing you'll ever build with a circular saw — and for good reason. Risers must land between 4 and 7¾ inches, treads need real depth, and the killer rule is consistency: every riser within ⅜ inch of the others, or every step is a trip hazard.

This calculator takes your total rise (floor to floor), divides by your target riser height, and rounds up to whole risers — then recomputes the actual riser height so all steps are identical. Treads are always risers minus one, and the run follows from your tread depth.

How to measure for stairs

  1. Measure total rise: finished floor to finished floor, in inches. Include the finished flooring thickness at both ends — subfloor measurements lie.
  2. Enter a target riser height around 7–7.5 inches (the comfortable zone). The calculator rounds up to whole risers and evens them out.
  3. Set tread depth to 11 inches (the 7-11 rule: ~7-inch risers, 11-inch treads). Deeper is fine; shallower is a code problem.
  4. Check the total run against your available space — stairs need more horizontal room than people expect.

Riser counts by total rise (target ≈ 7.5 in)

Total riseRisersActual riser height
8 ft (96 in)137.38 in
8 ft (96 in)146.86 in
9 ft (108 in)147.71 in
9 ft (108 in)157.20 in
10 ft (120 in)167.50 in

Risers = ceil(total rise ÷ 7.5). All heights shown are within the 4–7¾ in code range.

Worked example: stairs for an 8-ft ceiling

Total rise 96 inches (8-ft floor to floor), 7.5-in target risers, 11-in treads:

  1. Risers: 96 ÷ 7.5 = 12.8 → 13 risers (or 14 for a gentler step).
  2. With 14 risers: 96 ÷ 14 = 6.86 in per riser — even and code-legal.
  3. Treads: 14 − 1 = 13.
  4. Total run: 13 × 11 = 143 in (≈ 11 ft 11 in).

14 risers at 6.86 in, 13 treads at 11 in, ~11.9 ft of total run.

Pro tips for building stairs

  • The ⅜-inch rule is the one inspectors actually measure: the tallest and shortest riser in a flight must be within ⅜ inch. Cut one stringer template and trace it.
  • Headroom needs 6 ft 8 in minimum — measure diagonally from tread nosing to the ceiling above, not straight down.
  • Any flight with more than 12 ft of vertical rise needs a landing. Plan it before you cut stringers.
  • Build the stringers from the template, then test-fit before cutting the rest. One bad stringer is a lesson; six are a lumber bill.

How to use the stair calculator

1. Choose your unit system — Imperial (feet and inches) or Metric (meters and centimeters).

2. Enter the total rise — the vertical distance from the lower floor to the upper floor.

3. Enter your target riser height — typically 7 to 7.75 inches for comfortable stairs.

4. Enter the tread depth — typically 10 to 11 inches for residential stairs.

5. Click Calculate to see the number of risers, treads, total run, and stringer length.

How stair dimensions are calculated

The calculator divides the total rise by the target riser height and rounds up to get the number of risers. The actual riser height is then recalculated by dividing the total rise evenly across all risers, ensuring each step is exactly the same height.

The number of treads is one less than the number of risers, since the top riser lands on the upper floor. The total run is the number of treads multiplied by the tread depth. The stringer length is the diagonal distance calculated using the Pythagorean theorem.

Building code considerations for stairs

Most residential building codes (IRC) limit the maximum riser height to 7.75 inches and require a minimum tread depth of 10 inches. The greatest riser height within a flight of stairs cannot exceed the smallest by more than 3/8 inch.

Always check your local building codes before starting construction, as requirements can vary by jurisdiction. Handrails, headroom clearance, and stair width may also be regulated.

Stair calculator example

Suppose your total rise is 100 inches, your target riser height is 7.5 inches, and your tread depth is 11 inches.

Number of risers: 100 ÷ 7.5 = 13.33 — rounded up to 14 risers.

Actual riser height: 100 ÷ 14 = 7.14 inches per riser.

Number of treads: 14 − 1 = 13 treads.

Total run: 13 × 11 = 143 inches = 11.92 feet.

Stringer length: √(100² + 143²) = √(10,000 + 20,449) = √30,449 = 174.5 inches = 14.54 feet.

You need 14 risers, 13 treads, and a stringer approximately 14.54 feet long.

Frequently Asked Questions

How do I calculate the number of stair risers?+
Divide the total rise (the vertical height from floor to floor) by your target riser height. Round up to the nearest whole number to get the number of risers. For example, a 100-inch total rise with a 7.5-inch target riser height gives 13.33 — rounded up to 14 risers.
What is a comfortable riser height?+
A riser height between 7 and 7.75 inches is generally considered comfortable for most residential stairs. Building codes typically limit the maximum riser height to 7.75 inches (IRC) or 8 inches (some commercial codes). Risers below 4 inches can feel like a trip hazard and are not recommended.
What is the ideal tread depth?+
A tread depth of 10 to 11 inches is standard for residential stairs. Building codes typically require a minimum tread depth of 10 inches (IRC). Deeper treads are more comfortable but require more horizontal space. The calculator uses your tread depth to determine the total run.
What is a stair stringer and how long should it be?+
A stair stringer is the structural board that supports the treads and risers. Its length is the diagonal distance from the bottom of the stairs to the top, calculated using the Pythagorean theorem: the square root of (total rise squared + total run squared). You need at least two stringers for stairs up to 36 inches wide, and additional stringers for wider stairs.
How many treads do I need?+
The number of treads is always one less than the number of risers. The top riser lands on the upper floor, so it does not need a tread. For example, 14 risers means 13 treads. The calculator handles this automatically.

Related Guides

How Many Stair Risers Do I Need for an 8-Foot Ceiling?

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