Stair rise and run calculator

Stair rise and run calculator#

Enter the total floor to floor height. The calculator divides it into equal risers, checks each option against the IRC and Approved Document K limits, and reports the total run and the headroom you will need.

Inches Centimetres

Total floor to floor height in

Preferred going (tread depth) in

Rule setIRC, US residentialApproved Document K, UK privateAccessible, ADA and IBC

Nosing projection in

Enter your measurements above.

Riser heights are measured from the top of one finished tread to the top of the next, so the finished floor thicknesses at both ends have to be in the total height you enter.

Nothing you type leaves your browser: the maths runs on this page, and no values are stored or sent anywhere.

Finished floor to finished floor, and nothing else#

Total floor to floor height is the vertical distance from the finished surface of the lower floor to the finished surface of the upper floor. Not the subfloor, not the joist top, not the ceiling height of the room below. Every riser in the flight is that number divided by a whole number, so an error in it is repeated in every step and shows up as the one riser that trips people.

Take it with a tape held plumb at the position the flight will actually sit, then again at the other end of the opening. If the two differ, the floor is not level and that is a decision to make before you cut anything. Where the finishes are not yet chosen, add the intended build-up at both ends before you divide, and read the warning below for what happens when only one end is counted. Build-ups are in floor transitions and threshold heights, and tread and riser thicknesses in stair tread and riser flooring dimensions.

The going is the second input, and it is a preference rather than a measurement. If you enter a going below the minimum for the rule set you have chosen, the calculator quietly raises it to the minimum and works with that.

IRC, Part K and ADA: 7.75 in, 220 mm and 7 in#

The gap between them is larger than it looks. A 220 mm rise with a 220 mm going passes the calculator's Part K check and fails the IRC on both counts, and Approved Document K separately caps a private stair at a 42 degree pitch, which that combination breaks. An accessible stair at 7 in and 11 in is 32 degrees. Take the same 108 in height at the minimum going each rule set allows: 14 goings of 220 mm is 121 in (3.08 m), 14 goings of 10 in is 140 in (3.56 m), and the accessible rules force 16 risers, so 15 goings of 11 in is 165 in (4.19 m). Nearly 4 ft of floor separates them, for the same climb. The full set of code figures and where they come from is in stair dimensions: rise, run, headroom and handrails and the codes themselves in standards, codes and sources.

108 in divided 14, 15, 16 and 17 ways#

Height 108 in, preferred going 10.5 in, IRC.

1. Minimum number of risers: 108 divided by 7.75 is 13.9, so 14 is the fewest that stay legal.
2. Fourteen risers: 108 divided by 14 is 7.71 in each. Legal, but 0.04 in off the ceiling.
3. Fifteen risers: 7.20 in each. Sixteen: 6.75 in. Seventeen: 6.35 in.
4. Comfort test on each: 2R plus G. Fourteen gives 25.93, fifteen gives 24.90, sixteen gives 24.00, seventeen gives 23.21.
5. Fifteen risers is nearest to 25, so that is the recommendation: 15 risers at 7.20 in, 14 treads at 10.5 in.
6. Total run: 14 x 10.5 = 147 in (12 ft 3 in, 3.73 m).

Note step 6. A flight of 15 risers has only 14 goings, because the last riser lands on the upper floor, which is its tread. Counting 15 is the most common slip in stair setting out, and it puts the bottom step 10.5 in into a room with no space for it.

The six checks the panel runs on a flight#

Alongside the recommendation the calculator returns the checks that decide whether a flight is buildable: riser against maximum, going against minimum, the 2R plus G figure against the 24 to 25.5 in comfort band, the headroom for the rule set, the floor opening needed to keep it, and the reminder that every riser must be within 3/8 in (10 mm) of every other. It then lists the next three ways of dividing the same height.

All of it runs in your browser as you type. Nothing you enter is sent anywhere, and no part of the answer comes back from a server.

Which of the four legal flights to build#

The calculator will tell you that four divisions of the height are legal. It cannot tell you which to build.

• Who uses it. A stair that a child and an older adult use daily wants the shallower option even at the cost of run. The changes in step negotiation with age are covered in child and older adult dimensions.
• What is at the bottom. A flight needs a landing at least as long as the stair is wide, and it must not discharge into a door swing or a route. Widths for the hall it lands in are in hallway widths that work.
• Handrails and guards. Neither appears in the output. Handrail height, guard height and baluster spacing are in stair trim, newel and balustrade dimensions.
• Where the storey height came from. If the height itself is still movable, that is the cheapest variable in the whole problem, and it is examined in ceiling heights and datum lines.

No winders, no handrails, no local amendments#

It sizes a single straight flight. It does not lay one out, and it is a planning tool rather than a shop drawing.

• No winders, landings or tapered treads. A landing resets the flight, so run each flight separately and add the landing depth between them.
• No stringer, carriage or newel sizes, no handrail geometry, no guard heights.
• No structural check on the opening, the trimmer joists or the header.
• No ramps: slopes, runs and landings for those are in ramp slopes, lengths and landing sizes.
• No local amendment: the figures it uses are the base national ones.

For the rest of the set, including the tools that size what goes at the top and bottom of the flight, see the calculators index.