The Stair Calculator is a tool for calculating the parameters involved in building stairs. Use the Basic Version to see every workable combination of steps for a given rise, or the Comprehensive Version to fix the rise or step count and add tread, headroom, and stringer-mount options. A fraction-to-decimal conversion table for common measurements is provided at the bottom of the page.
The stair calculator works out every key measurement you need to design and build a staircase — the number of steps, the height of each riser, the depth of each tread (run), the length and height of the stringers, and the overall angle of the stairs — from just the total rise and run of the space. It offers two modes. The Basic Version lists every workable combination of steps for your total rise so you can pick the one that feels most comfortable, while the Comprehensive Version lets you fix either the riser height or the number of steps and then fine-tune the design with tread thickness, headroom clearance, and the type of stringer mount. Whether you are building a deck stair, a basement staircase, or a set of porch steps, this tool turns a few measurements into a complete, code-aware cutting plan.
Building stairs looks simple but involves a surprising number of parameters and building-code rules. Getting the rise and run right is essential for both safety and comfort — stairs that are too steep or have inconsistent steps are a serious trip hazard. This calculator handles the geometry precisely so you can focus on building.
Start by measuring your total rise — the vertical distance from the lower finished floor to the upper finished floor — and the space available for the total run, the horizontal distance the stairs will cover. Then choose a mode:
Understanding the parts of a staircase makes the results much clearer.
The rise is the vertical height of a single step, measured from the top of one tread to the top of the next. Consistent riser heights are critical — even small variations between steps cause people to trip. Most building codes cap the maximum riser height at about 7.75 inches (19.7 cm).
The run, or tread depth, is the horizontal depth of a step from the front edge (nosing) to the riser behind it. Deeper treads are more comfortable to walk on. Codes typically require a minimum tread depth of about 10 inches (25.4 cm).
The total rise is the overall vertical height the staircase climbs; the total run is the overall horizontal distance it spans. These two numbers, together with your chosen riser height, determine everything else about the staircase.
A stringer is the structural board (often a 2×12) that runs along each side of the stairs and supports the treads and risers. The stringer length is the diagonal length of that board, and the stringer height is the vertical distance it spans — both important when buying lumber and laying out cuts.
The nosing is the part of the tread that overhangs the riser below it. It adds a little extra foot room without increasing the total run and is required by many codes (typically a projection of about 0.75 to 1.25 inches when treads are less than 11 inches deep).
The tread thickness is the thickness of the material used for the steps. It matters when cutting stringers because the first (bottom) step must be cut shorter by the thickness of one tread so that, once the tread is installed, every finished step is the same height.
Headroom is the vertical clearance measured plumb from the nosing line of the stairs to the ceiling or the underside of the floor opening above. Building codes generally require a minimum headroom of about 6 feet 8 inches (203 cm) so people can use the stairs without ducking.
With a standard mount, the top of the stringer attaches to the face of the upper framing, and the top step is one riser below the upper floor (the upper floor itself acts as the last "step"). With a flush mount, the top of the stringer is level with the upper floor, adding one more tread to the run. The mount type changes the number of steps and the stringer dimensions, which is why the calculator asks for it.
The calculator uses straightforward geometry. With the total rise H, a chosen number of risers N, and a run per step:
Rise per step = H / N
Number of steps (treads) = N − 1 (standard) or N (flush)
Total run = number of steps × run
Stringer height = H − rise (standard) or H (flush)
Stringer length = √(stringer height² + total run²)
Angle = arctan(rise / run)
When you fix the riser height and the total rise is not an exact multiple of it, the first (bottom) step is adjusted to absorb the remainder so all the other steps stay equal. When a tread thickness is specified, the first step is cut shorter by that thickness on the stringer, and the calculator reports both the structural first-step height and the finished height with the tread in place.
Building codes exist to make stairs safe and predictable. While requirements vary by jurisdiction, the most widely used residential values (based on the International Residential Code) include:
Always confirm the exact requirements with your local building department before construction, as codes differ at the local level and are periodically updated.
Beyond meeting code, well-proportioned stairs simply feel right to climb. Carpenters have long used "rules of thumb" that relate rise and run. Two of the most common are the rise-plus-run rule (one rise plus one run should total about 17 to 18 inches) and the 2R + T rule (twice the rise plus the tread should equal about 24 to 25 inches). A riser of around 7 inches paired with an 11-inch tread is often cited as an ideal, comfortable combination. The Basic Version of this calculator helps you find such a balance by showing several step counts at once, so you can choose the option whose rise and run feel most natural for your space.
While this calculator focuses on the geometry of a straight flight, it is worth knowing the common staircase configurations, because the same rise-and-run math underlies all of them. A straight staircase is the simplest and most common: a single, uninterrupted flight from one floor to the next. An L-shaped staircase turns 90 degrees, usually with a landing at the turn, which saves floor space and provides a natural resting point. A U-shaped (or half-turn) staircase doubles back on itself with a landing, fitting a tall rise into a compact footprint. Winder stairs replace a landing with wedge-shaped treads that turn the corner, saving even more space but requiring careful layout. Spiral and curved staircases wrap around a center point or sweep along a curve and are prized for their looks, though they are harder to build and less convenient for moving furniture. For any multi-flight design, you calculate the total rise across the whole staircase, then divide the rise and the steps among the individual flights, keeping every riser in the entire staircase the same height for safety. Landings themselves do not count as steps but must be at least as deep as the stair is wide.
The results from this calculator translate directly into a materials list. The stringer length tells you how long each stringer board must be — typically cut from pressure-treated 2×12 lumber for exterior stairs — and most straight flights need at least two stringers, with a third added down the middle for stairs wider than about 36 inches or for heavier loads. The number of steps tells you how many treads and risers to buy; treads are often 2× lumber or manufactured stair treads, while risers are thinner boards or plywood. When budgeting, remember to add fasteners, joist hangers or stringer connectors, any railing and balusters required by code, and finishing materials such as paint, stain, or anti-slip coating. Interior stairs may also involve skirt boards, nosing trim, and carpet or hardwood, which add to both cost and labor. Getting the rise and run right the first time avoids the single most expensive mistake in stair building — miscut stringers — which is exactly what this calculator is designed to prevent.
Tape measures are marked in fractions of an inch, but calculators work in decimals. Use this table to convert the calculator's decimal results into the nearest fraction when laying out cuts.
| Fraction | Decimal | Fraction | Decimal |
|---|---|---|---|
| 1/16" | 0.0625 | 9/16" | 0.5625 |
| 1/8" | 0.125 | 5/8" | 0.625 |
| 3/16" | 0.1875 | 11/16" | 0.6875 |
| 1/4" | 0.25 | 3/4" | 0.75 |
| 5/16" | 0.3125 | 13/16" | 0.8125 |
| 3/8" | 0.375 | 7/8" | 0.875 |
| 7/16" | 0.4375 | 15/16" | 0.9375 |
| 1/2" | 0.5 | 1" | 1.0 |
The Basic Version shows a table of every workable step count for your total rise, letting you compare options. The Comprehensive Version produces one detailed result for a fixed riser height or step count, and adds tread thickness, headroom clearance, and stringer-mount options.
A riser of about 7 inches (18 cm) with a tread of about 11 inches (28 cm) is widely considered comfortable. Codes generally allow risers up to 7.75 inches and require treads of at least 10 inches. The rise-plus-run rule (one rise plus one run ≈ 17–18 inches) is a good comfort check.
Divide the total rise by your desired riser height and round to a whole number of risers. The number of treads (steps you walk on) is usually one less than the number of risers for a standard mount, because the upper floor serves as the top step.
When the total rise does not divide evenly by the riser height, the remainder is placed in the bottom step so that all the other steps remain exactly equal. The calculator reports this first-step height for you. When a tread is added, the first step is also cut shorter by the tread thickness.
A standard mount attaches the stringer to the face of the upper framing, so the upper floor acts as the last step and there is one fewer tread. A flush mount makes the top of the stringer level with the upper floor, adding one more tread and increasing the total run and stringer length.
The stringer length is the diagonal of a right triangle whose vertical leg is the stringer height and whose horizontal leg is the total run: stringer length = √(stringer height² + total run²).
This Stair Calculator is provided for educational and general informational purposes. Results are computed with standard stair geometry and displayed to high precision, but building codes vary by location and are periodically updated. Always verify measurements and confirm all requirements with your local building authority before constructing stairs.