Field calculator
Stair rise and run calculator (riser height)
A safe, comfortable, code-legal stair starts with dividing the total rise into equal risers. This calculator takes the total rise (finished floor to finished floor), divides it by a target riser height near the comfortable range, rounds to a whole number of risers, then gives the exact riser height so every step is equal, plus the tread count (one fewer than the risers) and the total horizontal run from your tread depth. Enter the total rise in inches, a target riser, and a tread depth. Equal risers are not optional: an odd step out of the pattern is a trip hazard and a code violation. The maximum riser, minimum tread, the allowed variation between risers, headroom, and nosing are all set by the IRC or IBC and the local amendments, so confirm the layout and the rise-plus-run or 2R+T comfort rule against the adopted code and the AHJ before you cut stringers or set forms.
Result
Stair layout from the total rise: the number of risers is the total rise divided by a target riser height (commonly near 7 inches), rounded to a whole number, and the actual riser height is the total rise divided by that count so every riser is equal. The treads are one fewer than the risers, and the run is the tread count times the tread depth. Enter the total rise (finished floor to finished floor) in inches, a target riser, and a tread depth. Code sets the maximum riser, minimum tread, and the allowed variation between risers, so confirm the riser, tread, headroom, and nosing against the IRC or IBC and the AHJ.
Worked example
A stair climbs 108 in floor-to-floor. Size the risers near a 7 in target with 11 in treads.
- Total rise108 in
- Target riser7 in
- Tread depth11 in
- Number of risers = round(108 ÷ 7) = 15 risers.
- Actual riser height = 108 ÷ 15 = 7.2 in each (equal, as code requires).
- Treads = 15 − 1 = 14; total run = 14 × 11 = 154 in (12 ft 10 in).
15 equal risers at 7.2 in and 14 treads at 11 in need 12 ft 10 in of run. Check the riser/tread against your adopted code.
anvilfield.com/calculators/stair-rise-run-calculator · Free field calculators and FieldOS. A planning estimate, verify against the code, the manufacturer, and the engineer of record.
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Stair FAQ
What is concrete formwork?
Concrete formwork is the temporary mold that shapes fresh concrete plus the framing and hardware that hold it in place until the concrete sets. It has to hold the shape, resist the lateral pressure the wet concrete pushes back with, and leave the right finish, then strip clean. ACI 347 governs the design, and a failure is a collapse.
What is a gang form?
A gang form is many form panels joined into one rigid unit, sized so the whole assembly is set, stripped, and flown by crane as a single piece. It suits large, repeating walls and cores because fewer cycles mean fewer picks and faster pours. Gangs usually run reusable taper ties so they strip and fly clean every cycle.
What are form ties?
Form ties are the tension members holding the two faces of a wall form together against the outward pressure of fresh concrete, and they set the wall thickness. Snap ties are light duty, she-bolts and coil ties heavier, and taper ties pull fully out for gang forms. Space them to the pressure, tightest at the bottom of the form.
Why does formwork fail?
Formwork fails when it is loaded harder than it was designed for or stripped too early. A wall blows out from under-spaced ties or a pour rate that ran past the design, a tower buckles from poor bracing or bad bearing, and a slab drops when stripped before strength. Pour rate is the field cause that hides in plain sight.
Which formwork system should I use for a repetitive wall?
For a wall that repeats many times, a modular panel or gang system beats job-built lumber, because the cost spreads across the cycles and each set-and-strip is faster. Job-built wins on low-quantity, odd shapes. The break-even is repetition, so count the cycles honestly before you choose, and match the face material to the finish.