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Stair calculator: rise and run, stringer length and headroom

Units

Enter the total rise and the total run available (or the tread depth you want): the tool finds the number of risers that gives a comfortable riser height, then works out tread depth, the 2R + T check, angle, stringer length and headroom.

You can type the unit in any box: 9 ft 2 in, 9' 2", 7 3/4 in, 110 in, 2.7 m, 270 cm. Without a unit, imperial boxes read inches.

Comfort guidelines
Headroom under the stairwell opening

The stairwell opening is the hole in the upper floor, measured back from the top edge of the stairs. Headroom is measured plumb from the line of the tread nosings up to the underside of the floor, at the edge of the opening. Leave the opening blank to get the minimum length for your target headroom.

Examples
Result
    Stair profile drawn to scale
    Profile to scale: steps, upper floor, stairwell opening and headroom (red line).
    Possible layouts Green rows meet the comfort guidelines. "Choose" sets that number of risers.
    RisersRiser RTreadsTread T2R + TAngleTotal runPick
    Calculation steps

      Guidelines only. Required riser heights, tread depths, headroom, widths, handrails and guards depend on the country, the local code and the type of building (house, apartment block, public building). Check the code that applies where you live and have the plans checked by a professional or your building department.

      Your last values stay saved on this device.

      Plan a staircase from the total rise and run

      This stair calculator starts from two measurements: the total rise, from finished floor to finished floor, and the total run you have room for. It finds the number of risers that gives a comfortable riser height, works out the tread depth, checks it against the guideline you choose, then gives the angle, the stringer length and the headroom under the stairwell opening. A scale drawing and a table of possible layouts come with it; switch to metric at the top.

      Stair terms in plain words

      • Riser: the vertical part between two steps; its height is the rise per step.
      • Tread: where your foot lands; the run per step is measured nosing to nosing.
      • Stringer: the sloping board that carries the treads.
      • Stairwell opening: the hole in the upper floor.
      • Headroom: the clear height above the nosings, under the floor above.
      • Total run: the floor length the stairs take up.

      How to use it

      1. Pick the "Stair layout": straight, or two flights with a straight or L-shaped landing.
      2. Type the "Total rise (finished floor to finished floor)" and the "Total run available", or switch "Work from" to "the tread depth you want". Entries such as 9 ft 2 in, 9' 2" or 110 all work.
      3. Choose a rule under "Comfort guidelines" and adjust the ranges if needed.
      4. For headroom, enter the "Upper floor thickness" and the "Stairwell opening length".
      5. In "Possible layouts", "Choose" forces another number of risers.

      Step-by-step example

      Total rise 9 ft 2 in, which is 110 in, with 10 in treads. With 14 risers each one would be 7.857 in, above the 7¾ in limit, so the tool takes 15 risers of 110 ÷ 15 = 7.333 in (about 7 5/16 in). There are only 14 treads, because the last riser steps up onto the upper floor, which acts as the top tread. Total run: 14 × 10 = 140 in, or 11 ft 8 in. The angle is arctan(7.333 ÷ 10) ≈ 36.25°, and the stringer is √(110² + 140²) ≈ 178.04 in, about 14 ft 10 in before cuts.

      In metric, 2.70 m of rise and 3.60 m of run give 15 risers of exactly 18 cm and 14 treads of 25.71 cm, an angle of about 35° and a 4.50 m stringer.

      Headroom under the opening

      At the edge of the opening, headroom equals opening length × rise ÷ run − floor thickness. With a 10 in floor and a 10 ft (120 in) opening: 120 × 7.333 ÷ 10 − 10 ≈ 78 in, that is 6 ft 6 in, short of the 6 ft 8 in usually targeted. The opening would need (80 + 10) × 10 ÷ 7.333 ≈ 122.73 in, about 10 ft 2 3/4 in.

      Rules of thumb and building codes

      The International Residential Code, adopted with local changes by many US jurisdictions, sets among other things a maximum riser of 7¾ in, a minimum tread of 10 in and 6 ft 8 in of headroom. Your local code may differ, and guards, handrails and width have their own rules. In Europe, people use the Blondel formula, credited to a 17th-century French architect: two risers plus one tread should come to about one stride, 60 to 64 cm (24 to 25 in). Germany uses 63 cm. Treat all of these as guidelines and check with your building department or a professional.

      Landings and winding stairs

      With a landing there are two fewer treads than risers: total run = (risers − 2) × tread + landing. For winders, measure along the walking line, often in the middle of the stair width: straight parts + angle ÷ 360 × 2π × radius. Enter that length as the run of a straight stair; tread = length ÷ (risers − 1).

      Frequently asked questions

      How many steps for a 9 ft 2 in rise?

      Fifteen risers of 7.333 in and fourteen treads under the IRC limits, since fourteen risers would be 7.857 in each.

      Why one less tread than risers?

      The upper floor is the top step, so its depth is not counted.

      What is a comfortable riser height?

      Around 7 to 7½ in with a 10 to 11 in tread suits most people; much above 8 in feels steep.

      Does the result meet code?

      The tool compares your numbers with common guidelines, not with the code adopted where you live. Check it locally.