How to measure total rise
The total rise is the height from the finished floor at the bottom to the finished floor at the top. Finished is the word that matters: if the tile, the hardwood or the deck boards are not down yet, add their thickness at the top and take it off at the bottom. A staircase laid out between two subfloors ends with a first or a last riser that is not like the others.
Measure it plumb, not along a wall that leans, and at the place the stairs will stand: floors are rarely level over the length of a staircase.
How the number of steps is worked out
Divide the total rise by the tallest riser you will accept, and round the result up. Rounding up is what keeps every riser at or under the limit; rounding down would make each one taller than it. Then divide the rise by that number of risers: every riser is exactly that, and the last one is as tall as the first.
Worked example. A total rise of 108 in (9 ft), with risers of 7 3/4 in at most and treads 10 in deep.
- Risers: 108 ÷ 7.75 = 13.94, rounded up to 14
- Riser height: 108 ÷ 14 = 7.714 in, which a tape reads as 7 11/16 in
- Treads: 14 − 1 = 13
- Total run: 13 × 10 in = 130 in
- Angle: 37.65°. Stringer line: 169 in
There is one tread fewer than there are risers, because the floor above is the last step. When the rise divides evenly there is nothing to round: 105 in with a limit of 7 1/2 in is 14 risers of 7.5 in exactly.
Comfortable stairs
The limit is not the target. A lower riser and a deeper tread make an easier climb, at the price of a longer staircase. Two old rules of thumb, which Autodesk’s Revit help quotes from the Architectural Graphic Standards, put numbers on it: two risers plus one tread should come to between 24 and 25 in, and one riser plus one tread to about 17.5 in. The example is at 25.43 in: on the steep side.
To try a gentler stair, lower the riser limit and watch the run grow. If the run is what you are short of, choose “I have limited run”: the calculator keeps the fewest risers the limit allows and tells you how deep each tread can be. In 120 in of run, the same rise leaves treads of 9 1/4 in.
Landings, headroom and width
The calculator shows these reference values beside your figures. They are from the 2021 International Residential Code, as the Stairbuilders and Manufacturers Association quotes it; your town may have adopted another edition or changed it.
- Risers 7 3/4 in at most, treads 10 in at least, and within one flight neither may vary by more than 3/8 in.
- Nosing of 3/4 to 1 1/4 in.
- Headroom of 6 ft 8 in, measured up from the line of the nosings. Enter the height of the ceiling over the foot of the stairs and the drawing shows how long the opening above has to be: under an 8 ft ceiling, 119 in for the example.
- Width of 36 in at least, and a handrail 34 to 38 in above the nosings.
A landing breaks a long flight in two. Enter the riser it comes after and its depth: with a landing after riser 7, the example becomes two flights of 7 risers and 6 treads, 60 in of run each, 12 treads in all. Each flight then has a stringer line of its own, 80.7 in here, and the landing is part of the opening above.
From numbers to a stringer
The riser and the tread are the two settings of a framing square. The link under the result opens the stair stringer calculator on the same stairs: the marks along the board, the shorter first riser, what is left of the board under the notches, and the length to buy.
Questions about stairs
How many steps for a 9 ft ceiling?
Measure floor to floor, not floor to ceiling: the joists and the floor above add about a foot. For a total rise of 108 in, 14 risers of 7 11/16 in and 13 treads.
What is a good riser height?
The 2021 IRC allows up to 7 3/4 in. The rule of thumb of two risers plus a tread between 24 and 25 in gives about 7 in with a tread of 10 to 11 in.
Does the top floor count as a step?
It counts as a riser and not as a tread. You climb 14 risers and stand on 13 treads: the fourteenth step lands on the floor.
How much floor space does a staircase take?
Its total run by its width, plus a landing at each end. The example runs 130 in, a little under 11 ft; at 36 in wide that is about 33 sq ft of floor.
Sources
- Stairbuilders and Manufacturers Association, Visual Interpretation of the International Residential Code, 2021: Stair Building Code. IRC 2021 as quoted there. R311.7.1: stairways not less than 36 in in clear width. R311.7.2: headroom not less than 6 ft 8 in, measured from the sloped line adjoining the tread nosings or from the floor of a landing. R311.7.5.1: riser height not more than 7 3/4 in, the greatest within a flight not more than 3/8 in over the smallest. R311.7.5.2: tread depth not less than 10 in. R311.7.5.3: a nosing of 3/4 to 1 1/4 in. R311.7.6: a landing as wide as the flight it serves and, where the stairway has a straight run, not less than 36 in in the direction of travel. R311.7.8.1: handrail height 34 to 38 in. Read on .
- Autodesk, Revit help: Rule-of-Thumb Formulas for Stairs. From the Architectural Graphic Standards: riser + tread = 17.5 in; riser x tread = 75; two risers + one tread between 24 and 25 in. Read on .
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