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Stair Calculator

Enter total rise and tread depth to get exact riser height, stringer length, stair angle and IRC code-compliance flags — plus a profile diagram.

Total rise (floor to floor)

Target riser

Tread depth

Tread nosing

Calculated stair

  • Risers: 14
  • Riser height: 7.714 in
  • Treads: 13
  • Total run: 143.00 in
  • Stringer: 179.20 in
  • Angle: 37.1°
!Riser height 7.71 in is close to the 7.75 in code limit. Most builders aim for 7 to 7.5 in for comfort.
!2×riser + tread = 26.4 in. Comfortable stairs land between 24 and 25. Yours feel stretched.
!Stair angle 37.1° is steeper than the typical residential 30–37° range.
14 risers × 7.71 in · tread 11 in + 1 in nose

Side profile — risers vertical, treads horizontal. Dashed line shows the stringer line of run.

You'll need
179.2 in
14 risers × 7.71 in
+ 13 pieces of at 11 in deep

108 in total rise · 14 risers · 11 in tread + 1 in nose.

Materials list

Stair stringers (2×12)3 pieces
Minimum 3 stringers (left, right, center) for treads up to 36 in wide — add one more for wider stairs.
Stair treads13 pieces
13 treads at 11.00 in deep + 1 in nosing — buy pre-cut or rip from 5/4 stock.
Riser boards14 pieces
14 risers at 7.71 in tall — 1×8 primed pine is standard for closed risers.
Stringer brackets42 pieces
Steel angle brackets fasten each tread to each stringer — far stronger than nails alone.
Construction screws1 box
3 in exterior screws for stringer-to-rim and tread-to-stringer connections.

Tools you'll want

Buy-once items — skip any you already own.

Framing square
Lays out stringer cuts directly — stair gauges (small brass clips) lock the rise and run.
Circular sawoptional
Standard tool for cutting stringer notches — finish corner cuts with a hand saw to avoid over-cutting.

Where to buy (optional)

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Estimates only — verify quantities before buying.

How to calculate stairs

Stair design starts with the total rise — the vertical distance from the finished lower floor to the finished upper floor. Everything else is derived from it:

riserCount = round(totalRise ÷ targetRiser)   ← never fewer than 2
riserHeight = totalRise ÷ riserCount           ← every riser must match
treadCount = riserCount − 1                    ← upper floor is the "top tread"
totalRun = treadCount × treadDepth
stringer = √(totalRise² + totalRun²)
angle = arctan(totalRise ÷ totalRun)

The IRC residential limits are 7.75 in max riser, 10 in min tread, 3/8 in max variation between any two risers or any two treads, and 6 ft 8 in minimum headroom. Comfort lives in a narrower band: 7 to 7.5 in risers paired with 10.5 to 11.5 in treads.

Common mistakes

  • Measuring rise to the subfloor. Always measure to the finished floor surface — flooring thickness on the upper or lower level changes the top and bottom riser heights.
  • Letting risers vary. Code allows 3/8 in variation between the largest and smallest riser in the run. Anything more is a trip hazard you will feel every time you walk it.
  • Cutting all three stringers from one layout line. Slight saw drift compounds. Mark each stringer individually with a framing square and stair gauges, then test-fit before installing treads.
  • Forgetting the top tread is the floor. Number-of-treads is always one less than number-of-risers. Buy treads accordingly or you will end up with an extra board.

Frequently asked questions

How do I calculate the number of stair risers I need?+

Divide the total floor-to-floor rise by your target riser height — typically 7 to 7.5 inches for residential — and round to the nearest whole number. Then divide the total rise by that count to get the exact riser height. Every riser in the run must be the same height; building code allows a maximum variation of 3/8 inch between any two risers.

What is the IRC maximum riser height for residential stairs?+

The International Residential Code (IRC R311.7.5) caps residential riser height at 7.75 inches and requires a minimum tread depth (run) of 10 inches. The calculator flags any combination that exceeds the riser limit or falls below the tread minimum so you catch it before cutting stringers.

How do I figure out the stringer length?+

The stringer is the hypotenuse of the right triangle formed by the total rise and total run. Stringer length = √(total rise² + total run²). For a typical 108 in (9 ft) rise with 14 treads at 11 in each (154 in run), the stringer is about 188 in or 15 ft 8 in long — you will need 2×12 stock at minimum.

What is the 2R + T rule for comfortable stairs?+

A long-standing carpenter rule: two times the riser height plus the tread depth should land between 24 and 25 inches. So a 7 in riser pairs nicely with an 11 in tread (2×7 + 11 = 25). Stairs outside the 24-25 range feel cramped (too steep) or stretched (too shallow), even when each measurement is within code.

How wide should an indoor staircase be?+

IRC requires a minimum stair width of 36 inches measured above the handrail, with handrails projecting no more than 4.5 inches into that space. 36 inches is the legal minimum; 42 to 48 inches is more comfortable for moving furniture and feels less tight for two people passing.

What size lumber do I need for stair stringers?+

Stair stringers are almost always 2×12 stock — anything narrower leaves too little material between the notch cuts and weakens the stringer. Use pressure-treated lumber for exterior stairs and any stair in contact with concrete. Plan on a minimum of three stringers for treads up to 36 inches wide and four for wider stairs.

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Reviewed by the RenoSheets team for calculation accuracy. Method: integer riser count from rounded division, exact riser height from total rise ÷ count, IRC R311.7.5 residential limits flagged not enforced. Last updated 2026-06-02. Estimates only — verify dimensions against your local building code and field measurements before cutting stringers.