Give it the total floor-to-floor rise and it works out an even riser height, the treads, total run, stringer length and stair angle — with a labeled diagram so you can see the flight before you cut. Plus deck and spiral modes and a baluster spacing solver. This covers stair geometry; roof slope lives in the roof pitch calculator.
Units
Stair type
Measure after the finish floor is in — flooring added later changes the total rise.
~7″ is comfortable
~10–11″ typical
Adds to the footprint run. Size each flight’s stringer separately.
Spiral risers run taller, ~8–9.5″
From centre pole to outer edge
¾ turn = 270°, full turn = 360°
Clear distance the balusters fill, post to post.
A 4″ sphere must not pass — keep under 4″
A layout aid. Riser, tread, headroom and guard guidelines shown are general comfort and safety conventions — minimums vary by jurisdiction, so check your local building code before cutting stringers or ordering material.
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Building the stairs?
Pouring concrete steps instead? The Concrete Calculator has a stairs mode for the volume and bags. For deck stringers and treads, the Board Foot Calculator totals the lumber, and the Miter Angle Calculator gives saw angles for skirt and trim cuts.
Start from the total rise, not the step
The single most important measurement in a staircase is the total rise: the vertical distance from the finished floor at the bottom to the finished floor at the top. Everything else follows from it. The mistake that creates wobbly, trip-prone stairs is laying out every step at a target height and letting whatever is left over become an odd last step — uneven risers are the most common cause of stair trips.
The fix is to size the count first. Divide the total rise by a comfortable target riser (around 7″), round to a whole number of risers, then divide the total rise back by that count. Every riser comes out identical:
risers = round(total rise ÷ target riser) riser height = total rise ÷ risers treads = risers − 1 total run = treads × tread depth stringer = √(total rise² + total run²) angle° = atan(total rise ÷ total run)
The number of treads is one fewer than the risers because the top floor itself acts as the final landing.
What makes a staircase comfortable
Dimension
Comfortable range
Notes
Riser height
~7–7.75″ (178–197 mm)
Many codes cap the maximum near 7.75″
Tread depth
~10–11″ (254–279 mm)
Minimum often around 10″
2R + T
~24–25″ (610–635 mm)
Two risers + one tread comfort rule
Stair angle
~30–37°
Under 30° ramp-like; over 42° ladder-like
Riser variation
≤ ~3/8″ within a flight
Keep every riser equal
The calculator checks your layout against these and flags anything outside the comfortable band, so you can nudge the tread depth or riser height before you commit. These are widely used conventions; minimums vary by jurisdiction — check your local building code.
Stringers, decks and concrete
The stringer is the diagonal of the rise-and-run triangle. After you notch it, leave enough uncut depth in the board for strength — commonly at least about 3.5–5″. Deck stairs use the same math; the difference is exterior lumber, a slight tread slope for drainage, and footings at the base. For concrete steps, the geometry is identical but you are pouring solid forms, so size the formwork here and then take the dimensions to the concrete calculator for the volume and bag count.
Spiral stairs and baluster spacing
A spiral stair stacks wedge-shaped treads around a centre pole. The riser layout works the same way — even risers from the total rise — while the rotation per tread comes from your total turn divided by the number of treads. The walkline depth (measured part-way out from the pole) and headroom are what make it usable. For guards and railings, balusters are spaced so a 4″ sphere cannot pass between them; the baluster mode solves the smallest number of spindles that keeps every gap, including the end gaps, equal and under that limit.
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Frequently asked questions
How many steps do I need for a given total rise?
Divide total rise by a target riser (~7″) and round to a whole number for the riser count, then divide total rise back by that count for the even riser height. A 108″ rise ÷ 7 = 15.4 → 15 risers → 7.2″ each. Treads = risers − 1, since the top floor is the last landing.
How do I make the riser heights even?
Don’t cut every step at the target and let the last one absorb the remainder — that odd step is the classic trip. Pick the whole riser count first, then divide total rise by it so all risers match. This tool does that, and an even layout also keeps you within the ~3/8″ riser-variation limit many codes set.
How do I calculate stringer length?
Stringer = √(total rise² + total run²), with total run = tread depth × treads. A 108″ rise with 14 treads at 10.5″ gives a 147″ run and a stringer of √(108² + 147²) ≈ 182.4″ (~15′ 2″). Leave enough uncut depth in the board after notching — commonly ~3.5–5″ for strength.
What is a comfortable stair angle?
About 30–37° for most stairs. Under ~30° feels like a ramp and uses more floor; over ~42° feels ladder-steep. A 7″ riser with a 10.5–11″ tread is ~33–34° — the sweet spot. The tool reports the angle and flags it when the layout drifts out of range.
What is the 2R plus T rule for stairs?
Two riser heights plus one tread should total ~24–25″ (60–64 cm). It captures how far your foot travels up and forward per step. If your layout falls well outside that, the stairs feel cramped or stretched even when each dimension looks fine; adjust riser or tread to bring 2R+T back into range.
How far apart should balusters or spindles be spaced?
Keep the gap under 4″ so a 4″ sphere can’t pass. Take the rail length, set a max gap, and solve the smallest number of balusters that keeps every gap (including the end gaps) equal and under that max. The baluster mode reports the count and exact even gap. Exact limits vary by jurisdiction — check your local code.