How many steps do I need for my floor height?

Divide your floor-to-floor height by your preferred riser height, then round to the nearest whole number. That gives you your step count. Then divide your floor height by that step count to get the exact riser. For example, a 2,700 mm floor height at a preferred 175 mm riser gives 15.4 steps, which rounds to 15. Exact riser = 2,700 / 15 = 180 mm. This calculator does that automatically.

What is a comfortable riser height and tread going?

Most residential stairs feel comfortable with risers between 170 mm and 190 mm (6.5–7.5 in) and a tread going between 250 mm and 300 mm (10–11.5 in). Steeper risers feel tiring to climb; shallow risers with short going feel shuffly and awkward. Local building codes set the legal minimums and maximums, which vary by country and state.

What is Blondel's rule?

Blondel's rule is a traditional comfort formula: 2 × riser + going should equal roughly 600–640 mm (23.6–25.2 in). It captures the natural stride length of an adult walking uphill. A result below 600 mm usually means the stair is too shallow or the going is short; above 640 mm means it's too flat with oversized treads. This calculator reports your 2R+G value so you can check it against the comfort band.

How do I calculate stringer length?

Stringer length is the diagonal distance from the base of the stair to the top. The formula is: square root of (total rise squared + total run squared). For a flight with a 2,700 mm rise and 3,575 mm run, stringer length = sqrt(2700² + 3575²) = approximately 4,480 mm. This calculator computes stringer length per flight based on the risers and treads assigned to each one.

What is the difference between straight, L-shape, and U-shape stairs?

Straight stairs run in a single uninterrupted flight from one floor to the next. L-shape stairs turn 90 degrees with a landing between two flights, useful for fitting stairs into a corner. U-shape stairs (also called switchback stairs) use two 90-degree turns with landings, reversing direction completely. U-shapes reduce the floor footprint but need more wall space on both sides.

Stair Calculator – How Many Steps Do I Need?

Unit system

Stair type

Stair width

metres

Floor-to-floor height

metres (finished floor to finished floor)

Preferred riser height

mm (typical 170–190 mm)

Preferred tread going

mm (typical 250–300 mm)

Riser presets:

Minimum headroom

metres (typical 2.0–2.1 m)

Nosing overhang

mm (typical 15–30 mm)

Baluster max spacing

mm (for baluster count estimate)

How to Calculate Stair Dimensions

The core of any stair calculation is this: divide your floor-to-floor height by a whole number of risers to get the exact riser height, then decide how much horizontal space each tread takes up. Those two numbers determine everything else — angle, stringer length, headroom, and materials.

The process looks simple, but the tricky part is that riser count must be a whole number (you can't have half a step), which means your actual riser height rarely matches your preferred one exactly. This calculator finds the closest whole-number riser count to your preferred height, recalculates the exact riser, and flags if the result falls outside comfortable ranges.

Common Floor Heights — Step Count Reference

Floor-to-floor height	Steps (@ 175 mm riser)	Exact riser	Total run (@ 275 mm going)	Stringer length
2,400 mm (7 ft 10 in)	14	171 mm	3,575 mm	4,211 mm
2,550 mm (8 ft 4 in)	15	170 mm	3,850 mm	4,476 mm
2,700 mm (8 ft 10 in)	15	180 mm	3,850 mm	4,536 mm
2,850 mm (9 ft 4 in)	16	178 mm	4,125 mm	4,814 mm
3,000 mm (9 ft 10 in)	17	176 mm	4,400 mm	5,094 mm
3,300 mm (10 ft 10 in)	18	183 mm	4,675 mm	5,520 mm

Based on 175 mm preferred riser, 275 mm going. Stringer = sqrt(rise² + run²). Verify against your exact floor height.

Stair Type Comparison

Type	Flights	Best for	Space needed	Notes
Straight	1	Narrow corridors, garages, basements	Long floor footprint	Simplest to build; easiest to move furniture
L-shape	2	Corner locations, main floor stairs	Corner of a room	Landing breaks the climb; more complex framing
U-shape	3	Compact floor plans, split-level homes	Two parallel walls	Reduces footprint; hardest to estimate headroom

Formulas Used

All calculations use these standard relationships:

Step count (N): round(floor height / preferred riser), then exact riser = floor height / N
Stair angle: arctan(riser / going), in degrees
Stringer length per flight: sqrt(flight rise² + flight run²)
Blondel comfort check: 2 × riser + going, target 600–640 mm (23.6–25.2 in)
Headroom estimate: floor height minus (riser/going × opening length)

A note on headroom

The headroom estimate here is a straight geometric approximation. It does not account for joist depth, ceiling slope, or landing beam depth. Treat it as a ballpark check, not a construction measurement. For anything close to the minimum, measure on site with a string line along the stair slope.

Frequently Asked Questions

Divide your floor-to-floor height by your preferred riser height and round to the nearest whole number. That's your step count. Then divide floor height by that number to get the exact riser. For a 2,700 mm floor at 175 mm preferred riser: 2,700 / 175 = 15.4, rounds to 15 steps. Exact riser = 2,700 / 15 = 180 mm. The calculator above does this automatically and flags if the result sits outside a typical comfort range.

Most residential stairs feel right with risers between 170 mm and 190 mm (6.5–7.5 in) and tread going between 250 mm and 300 mm (10–11.5 in). Risers much above 190 mm feel tiring to climb; anything below 150 mm feels like shuffling. Going below 220 mm is too short for a comfortable footfall. Local codes set legal limits which vary by country and state, so check your jurisdiction before finalising dimensions.

Blondel's rule is a comfort check from 17th-century French architect François Blondel: 2 × riser + going should equal 600–640 mm (23.6–25.2 in). The logic is that it approximates the natural stride length of a person walking uphill. A result below 600 mm usually means a shallow stair with short going; above 640 mm means a very flat stair. It's a guideline, not a code requirement, but it's a useful sanity check before cutting timber.

Stringer length is the diagonal distance along the slope of the stair. The formula is sqrt(total rise² + total run²). For a flight with a 2,700 mm rise and 3,850 mm run: sqrt(2700² + 3850²) = sqrt(7,290,000 + 14,822,500) = sqrt(22,112,500) = approximately 4,703 mm. You need this to buy the right stringer timber length with enough room for the top and bottom cuts.

The simplified estimate here measures how much rise accumulates over the horizontal length of the floor opening, then subtracts that from the floor-to-floor height. If your opening is 1.2 m long and your riser/going ratio is 0.65, you lose about 780 mm of height at the start of the opening, leaving roughly 1,920 mm of clearance. This doesn't include joist depth or ceiling framing, so for anything tight, always check on site with a plumb bob and tape measure.

Straight stairs run in one unbroken flight. They're the easiest to build and the easiest for moving furniture, but they need a long continuous floor space. L-shape stairs turn 90 degrees with a flat landing between two flights, which suits corner locations and breaks the climb. U-shape stairs reverse direction completely across two landings, reducing the floor footprint at the cost of needing clearance on both sides. Risers and going are the same across all three types — what changes is how the total run is distributed across the available floor plan.

Staircase Planning Checklist

Reviewed by Liam Santos (framing carpenter). Covers floor opening size, joist trimming, stringer layout, tread and riser fixing, handrail height, baluster spacing, and final inspection points before sign-off.

Download Checklist (PDF)

Planning reference only. See Methodology and Data Sources. View all project checklists →

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Accuracy & Review

Reviewed by: Liam Santos

Liam is a framing carpenter with experience across residential stair builds, deck structures, and timber framing. He reviewed the step count logic, riser/going comfort ranges, Blondel check, stringer formula, and headroom estimate methodology used in this calculator.

Last updated: June 4, 2026

See: Methodology · Data Sources · Review Board

Disclaimer: These estimates are for general planning purposes only. Actual stair dimensions depend on local building codes, structural conditions, floor finish thicknesses, and on-site measurements. Always verify against current code requirements and consult a qualified builder or engineer before construction.

See Methodology and Data Sources for calculation assumptions.