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Stair Calculator

Number of steps, riser height, tread depth, stringer length and angle from your total rise.

How this is calculated

Risers = round(total rise ÷ preferred riser). Actual riser = total rise ÷ risers. Treads = risers − 1. Total run = treads × tread depth. Stringer = √(rise² + run²). Comfort rule: 2 × riser + tread ≈ 24–25 in (62–64 cm).

Enter the total vertical rise (floor to floor or deck to ground), your preferred riser height and tread depth. The calculator picks the best step count, checks it against common code limits and comfort rules, and gives stringer length, angle, lumber and cost.

Results are estimates for planning purposes only. Real-world quantities depend on site conditions, materials and workmanship. Always verify measurements, follow local building codes and confirm quantities with your supplier or a qualified professional before ordering or building.

About the Stair Calculator

Stairs feel wrong when the math is off by even half an inch — uneven risers are a trip hazard and a code violation. This calculator takes your total rise (floor to floor, or ground to deck surface) and produces a full cut list: riser count, exact riser height, tread depth, total run and stringer length. It targets the comfortable 7-inch riser and 11-inch tread that building codes are built around.

How to use

  1. Measure the total rise: vertical distance from the finished lower floor to the finished upper surface.
  2. Enter that rise in inches — for example, 105 inches for a deck 8 feet 9 inches high.
  3. Enter a target riser height if you have one; otherwise the calculator aims for about 7 inches.
  4. Choose tread depth: 11 inches is the comfortable standard, 10 inches the code minimum.
  5. Use the cut list: riser count, actual riser height, tread count, total run and stringer board length.

Understanding your results

Riser count is the number of steps; actual riser height divides the total rise evenly so every step is identical — the critical safety number. Treads equal risers minus one. Total run is how far the stairs extend out; stringer length is the diagonal board measurement for cutting.

How the calculation works

Riser count is total rise divided by the target riser height (about 7 inches), rounded up. Actual riser height is total rise divided by that count, and must stay at or under 7.75 inches per the International Residential Code. Total run is treads times tread depth. Stringer length is the hypotenuse: the square root of rise squared plus run squared.

Stair Calculator FAQs

The International Residential Code caps riser height at 7.75 inches, with a minimum tread depth of 10 inches. All risers in a flight must be uniform within 3/8 inch of each other — that variation limit is what inspectors actually measure. For comfort, most builders aim for a 7-inch riser with an 11-inch tread, which feels natural to climb.
Divide the total rise by 7 and round up. For example, a 105-inch rise divided by 7 gives exactly 15 risers at 7 inches each. If the rise were 100 inches, 100 divided by 7 is 14.3, so you round up to 15 risers at 6.67 inches each. Always round up — rounding down would push riser height over the comfortable range.
Multiply the number of treads (risers minus one) by the tread depth. Fifteen risers means 14 treads; at 11 inches per tread the total run is 154 inches, or about 12 feet 10 inches. That run measurement tells you how much floor space the stairs need and where the bottom step lands — critical for deck stairs near property lines.
Code requires at least 6 feet 8 inches of headroom measured vertically from the tread nosing to the ceiling above. In practice, allow more — tall people ducking under a stairwell is a daily annoyance. When cutting a stairwell opening in a floor, the opening usually needs to extend well past the bottom step to maintain clearance.
Use at least three stringers for a standard 36-inch-wide staircase — one on each side and one in the middle. Wider stairs need a stringer roughly every 16 inches, so a 48-inch-wide stair gets four. Cut stringers from 2×12 lumber; the diagonal cut must leave at least 3.5 inches of solid wood at the narrowest point for strength.
Nabil Sharif, founder of CalcDune

Written by

Nabil Sharif

Founder of CalcDune — a free library of 137 online calculators for finance, health and everyday math. Every calculator shows the formula behind its result, so you can see exactly how your numbers are worked out.

More articles by Nabil →

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