Stair Rise and Run: How to Calculate Stairs Correctly
Understand stair rise and run, the 7-11 rule, IRC code limits, and how to lay out a stringer correctly, with a code reference table and a worked example.
Stairs that feel comfortable and safe are not an accident; they follow a precise relationship between two measurements known as rise and run. Get that relationship right and people climb without thinking about it. Get it wrong, even by half an inch per step, and the staircase feels steep, awkward, or dangerous, and may fail inspection. Whether you are building a deck stair, a basement run, or a full interior staircase, understanding rise and run is the foundation of the whole job. This guide explains what rise and run mean, how to calculate them, the building-code limits you must respect, and how to lay out a stringer correctly.
Rise and run: the two core measurements
Every staircase is defined by two repeating dimensions. The rise is the vertical height of a single step, measured from the top of one tread to the top of the next. The run (also called the tread depth or "going") is the horizontal depth of a single step, the part your foot lands on, measured from the front edge of one tread to the front of the next.
Two more terms describe the staircase as a whole. The total rise is the full vertical distance the staircase climbs, from the lower finished floor to the upper finished floor. The total run is the full horizontal distance the staircase covers from the first riser to the last. Designing a staircase means dividing the total rise into a number of equal individual rises, and the total run into the same number of individual runs.
How to calculate the number of steps
Everything starts with the total rise, the floor-to-floor height. Suppose that distance is 108 inches. To find the number of steps, divide the total rise by a comfortable target rise, usually around 7 inches:
108 ÷ 7 = 15.4. Since you cannot have a fractional step, round to a whole number: 15 steps. Then divide the total rise back by that whole number to get the exact rise per step: 108 ÷ 15 = 7.2 inches per riser. Every riser in the staircase must be this same height. Uneven risers are the leading cause of stair trips, which is why code limits the variation between the tallest and shortest riser to just 3/8 of an inch across the whole flight. Our stair calculator does this division for you and flags any value that falls outside code.
The ideal rise-to-run relationship
Comfortable stairs balance rise against run. A tall rise with a shallow run is steep and tiring; a short rise with a deep run forces an unnatural stride. Carpenters have used rules of thumb for centuries to keep the two in proportion. The most common is:
Rise + Run should equal about 17 to 18 inches.
So if your rise is 7 inches, the run should be about 10 to 11 inches. Another classic formula states that 2 × rise + run should fall between 24 and 25 inches, which captures the way the body moves over a step. Both rules point to the same sweet spot: roughly a 7-inch rise paired with an 11-inch run, often called the "7-11" rule, produces stairs almost everyone finds comfortable.
Building code limits you must follow
The International Residential Code (IRC), which most U.S. jurisdictions adopt, sets hard limits on stair dimensions. These are not suggestions; an inspector will check them. Always confirm your local code, but the common IRC residential values are:
| Dimension | IRC residential limit |
|---|---|
| Maximum riser height | 7 3/4 in |
| Minimum tread depth (run) | 10 in |
| Maximum variation between risers | 3/8 in |
| Maximum variation between treads | 3/8 in |
| Minimum stair width | 36 in |
| Minimum headroom | 6 ft 8 in |
| Handrail height above nosing | 34 – 38 in |
| Nosing projection (where required) | 3/4 – 1 1/4 in |
Note that commercial and public stairs follow different, generally more generous, rules (often a 7-inch max rise and 11-inch min run). The figures above are for typical residential construction. Enter your numbers into the rise and run calculator to confirm each step stays within these limits before you cut anything.
What a stringer is and how to lay it out
The stringer is the sawtooth-cut board, usually a 2x12, that supports the treads and risers along each side of the staircase. Laying out a stringer means marking those sawtooth notches accurately so each step has the correct rise and run. The traditional tool is a framing square fitted with stair gauges (small brass stops) set to your rise on one leg and your run on the other.
- 1. Attach the stair gauges to the framing square at your calculated rise (say 7.2 in) and run (say 10.5 in).
- 2. Place the square near the end of the 2x12 and trace the right-angle formed by the two legs. This marks the first step's rise and tread.
- 3. Slide the square along, lining the gauge up with the previous mark, and trace again. Repeat for every step.
- 4. Mark the bottom cut and the top plumb cut where the stringer meets the floor and the upper landing.
A critical detail is the bottom step adjustment: you must subtract the thickness of one tread from the bottom rise. Because the bottom stringer sits on the floor but the tread adds thickness on top of every step, leaving the bottom riser uncut would make that first step too tall. Trimming the bottom by the tread thickness keeps every finished step equal. This "dropping the stringer" step trips up many first-time builders, so check it carefully or let the stair stringer calculator account for tread thickness automatically.
A worked example
Say you are building deck stairs with a total rise of 44 inches. Divide by a 7-inch target: 44 ÷ 7 = 6.3, round to 6 steps. Then 44 ÷ 6 = 7.33 inches per riser, which is under the 7 3/4-inch maximum, so it passes. For the run, choose 11 inches; check the rule of thumb: 7.33 + 11 = 18.33, comfortably in the 17 to 18 range. With 6 risers there are 5 treads between the floors (the top "step" is the landing or deck surface itself), so the total run is 5 × 11 = 55 inches. That tells you how far out from the deck the stairs will land, which matters for footing placement.
Why the step count and tread count differ
A frequent point of confusion: a staircase always has one more riser than it has treads. That is because the top riser brings you up to the landing or upper floor, which is not a tread you cut into the stringer. So a flight with 15 risers has 14 treads. Keeping this straight prevents you from ordering one tread too many or, worse, miscalculating the total run.
Common mistakes
The most dangerous error is inconsistent risers, where the first or last step ends up a different height because the floor or landing thickness was not accounted for. Even a 3/4-inch difference causes trips. The second is forgetting headroom; a steep stair in a tight basement can leave a low beam right where someone's head passes. Third is ignoring nosing and tread overhang when calculating run, which changes how deep the usable foot space actually is. Finally, builders sometimes skip the handrail height check, which is a guaranteed inspection failure. Running your design through a calculator and against the code table above catches most of these before they become expensive.
Measuring the total rise correctly before you cut anything
Almost every stair-building error traces back to one number that was measured carelessly: the total rise. The total rise is the vertical distance from the surface of the lower finished floor to the surface of the upper finished floor. The word "finished" is doing a lot of work in that sentence. If you measure from a bare subfloor at the bottom but the top landing already has 18 mm of hardwood and underlay installed, your stair will end up short by exactly that thickness, and the final step will feel wrong underfoot for the rest of the staircase's life.
The safest practice is to account for every finish layer at both levels before you do any arithmetic. Add the thickness of tile, hardwood, laminate, carpet plus its pad, or self-leveling compound to whichever level still needs it, and subtract nothing you cannot see. A laser level or a long straightedge with a spirit level laid across the opening gives you a clean reference line; tape-measuring down from that line in two or three places along the opening reveals whether the floor is level or whether you are dealing with a slope that will quietly distort your rise.
On exterior stairs and deck stairs the same logic applies but the ground rarely cooperates. Soil settles, concrete pads slope for drainage, and the "ground" you measure to today may not be the ground you walk on after the first rain. For deck stairs, measure to the point where the bottom of the stringer will actually land, and if that point is bare earth, plan a concrete pad or a precast block so the bottom step does not sink over time and turn a code-compliant rise into a trip hazard.
Headroom, total run, and the space the staircase will really occupy
Rise and run determine the shape of each step, but two other dimensions decide whether the staircase physically fits the building: headroom and total run. Headroom is the vertical clearance measured from the leading edge (the nosing) of any tread, straight up to the ceiling, soffit, or floor structure above. Building codes in both the US and the UK demand generous headroom because a staircase that forces a tall person to duck is genuinely dangerous when carrying laundry or boxes. As a planning figure, US residential codes commonly require a minimum of 6 feet 8 inches (about 2,030 mm) and UK guidance under Approved Document K targets 2,000 mm over the pitch line, with a reduced allowance for loft conversions.
Total run is the horizontal floor distance the staircase consumes from the face of the bottom riser to the face of the top riser. It is simply the number of treads multiplied by the going (the horizontal depth of each tread). People routinely underestimate this. A flight that climbs a normal 9-foot story can easily eat 10 to 13 feet of floor, and that footprint has to land somewhere sensible at the bottom, clear of doors that swing into the path and clear of the walking route through the room.
| Dimension | What it controls | Typical US guide | Typical UK guide |
|---|---|---|---|
| Total rise | Number of steps | Floor-to-floor, finished | Floor-to-floor, finished |
| Headroom | Clearance overhead | ≈ 6 ft 8 in (2,030 mm) | ≈ 2,000 mm over pitch line |
| Going (tread depth) | Comfort of footing | ≥ 10 in nominal | ≥ 220 mm typical |
| Pitch / angle | Steepness | ≈ 30–37° | ≤ 42° max |
Before committing to a design, sketch the total run on the actual floor plan with a tape measure or chalk line. Seeing the footprint at full scale on the floor catches conflicts that never show up on paper, such as a stair that ends a few inches into a doorway or blocks a window.
Landings, winders, and breaking up a long flight
A single straight flight is the simplest stair to build, but tall stories and tight footprints often force you to turn the stair or split it. A landing is a flat platform inserted into the run. It serves two purposes: it changes direction (an L-shaped or U-shaped stair) and it provides a rest and a safety break so that a fall cannot carry a person down the entire height of the building in one uninterrupted tumble. Many codes limit the vertical rise allowed between landings, so on a very tall climb a mid-flight landing is not optional.
When a landing replaces several treads, remember that the landing itself counts as one giant tread in your rise calculation. Its surface must sit exactly one riser height above the tread below it and one riser height below the tread above it. Get that wrong and you create the single most dangerous defect in stair building: an inconsistent riser right where people change direction and are least likely to be looking down.
Winders are pie-shaped treads that turn a corner without a flat landing, saving space at the cost of complexity and a degree of risk. They are popular in older UK homes and in cottages where floor area is precious. The hazard with winders is that the going narrows toward the inside of the turn; codes therefore specify a minimum going measured at a defined distance from the narrow end (often the centerline or a set distance such as 270 mm in from the inside). If you are planning winders, model them carefully and confirm the minimum going at the walk line before cutting anything.
Nosing, tread overhang, and why it changes the numbers
The nosing is the lip of the tread that projects out beyond the face of the riser below it. It exists to give your foot a little more landing area than the structural going alone provides, which makes descent feel safer. This introduces a subtle distinction that trips up beginners: the going (the horizontal advance per step, used for run and pitch calculations) is measured nosing-to-nosing, whereas the tread depth a person's foot actually rests on includes the overhang.
Codes set both a recommended nosing projection and a maximum, because too large an overhang becomes a toe-catcher on the way up. A projection in the region of 20–25 mm (about three quarters of an inch to one inch) is common. On open-riser stairs there is no riser face, so the rules about the gap between treads come into play instead, typically requiring that a sphere of a defined diameter cannot pass through, to protect small children.
Open risers, closed risers, and material choices
Whether your stair has solid riser boards (closed) or open gaps (open-riser) affects more than appearance. Closed risers are stronger against racking, hide the structure, and stop objects and small feet slipping through. Open risers feel lighter and more contemporary and let light pass through, but they demand attention to the gap rule and tend to feel less reassuring underfoot to nervous or elderly users.
Material also influences your rise-and-run tolerances. Solid timber treads can be planed and sanded slightly, giving you a small margin to correct a minor error. Concrete and steel stairs offer no such forgiveness; the layout must be exact before fabrication. Carpeted stairs hide a multitude of small inconsistencies but can also disguise a dangerous variation that a bare timber stair would have revealed. Whatever the material, the cardinal rule is unchanged: every riser the same height, every going the same depth, across the entire flight.
The 3-4-5 method and squaring your stringer layout
When you transfer rise and going onto a stringer, you are effectively drawing a series of right-angled triangles down a board. Any error in squareness compounds with each step, so the bottom of a long stringer can drift badly out of position even if each individual mark looked fine. The classic carpenter's check is the 3-4-5 rule: a triangle with sides of 3, 4, and 5 units (any consistent unit) is guaranteed to contain a perfect right angle. Mark 3 units along one line and 4 along the perpendicular; if the diagonal between those marks measures exactly 5, your corner is square.
A framing square with stair gauges (small brass fixtures that clamp to the square at your rise and going figures) is the traditional tool for marking stringers, letting you step off identical triangles down the board quickly. Whichever method you use, verify the first and last steps against the total rise and total run before you cut. It is far cheaper to re-check a pencil line than to discover an error after the saw has done its work. If you would rather let software handle the triangle math and the riser-spacing, our stair calculator takes your total rise and target step dimensions and returns the exact riser height, going, number of steps, and stringer length to mark out.
Comfort formulas beyond the basic ratio
The familiar "rise plus run" comfort rules exist because the human stride is remarkably consistent, and a staircase that ignores it feels tiring or treacherous even when it passes code. Three formulas are worth knowing because they each capture a different aspect of comfort.
| Formula | Target | What it captures |
|---|---|---|
| 2R + G | ≈ 24–25 in (610–635 mm) | Natural stride length on stairs |
| R + G | ≈ 17–18 in (430–460 mm) | Overall step proportion |
| R × G | ≈ 71–74 in² (≈ 45,000 mm²) | Balance of steepness and depth |
If a proposed rise and going satisfy all three, the staircase will feel natural to almost everyone. If it satisfies only one, treat that as a warning that the steps may be uncomfortably tall and shallow, or low and deep. These checks are especially valuable when you are squeezed for space and tempted to push the rise higher than ideal just to save a step or two of run.
US and UK code differences worth flagging
Builders who work from American tutorials and then apply them in Britain (or vice versa) can land in trouble because the two regimes express limits differently and pick different priorities. US codes (rooted in the IRC) often cap maximum riser height around 7 ¾ inches and set a minimum tread depth near 10 inches, and they place a strict 3/8-inch limit on the variation between the largest and smallest riser in a flight. UK guidance under Approved Document K speaks in millimetres, caps the pitch of a private stair at 42 degrees, and constrains the combination of rise and going rather than dictating each in isolation, with private, utility, and general-access stairs each having their own band.
The practical takeaway is to design to whichever code governs the building, confirm the current local amendments (jurisdictions frequently tweak the national baseline), and never assume a staircase that is legal on one side of the Atlantic automatically complies on the other. When in doubt, the more conservative limit is the safer one to build to.
Pre-cut checklist to avoid an expensive mistake
- Re-measure total rise to finished floor levels at both top and bottom, in at least two places.
- Confirm headroom along the full pitch line, not just at one point.
- Divide the rise into equal risers and check each riser falls within code.
- Verify the total run physically fits the floor plan, clear of doors and traffic.
- Check rise and going against the 2R+G comfort formula.
- Square the stringer layout with the 3-4-5 method before cutting.
- Plan landings or winders where the flight is too tall for a single straight run.
- Allow for nosing projection and the open-riser gap rule if relevant.
Treat the first stringer as a template only after it has passed every item above. Cut it, set it in place, and test it against the opening before mass-producing the rest. The hour spent checking is trivial against the cost and danger of a staircase with a rogue riser.
Frequently asked questions
What is the ideal stair rise and run?
A rise of about 7 inches paired with a run of about 11 inches, the "7-11" rule, is widely considered ideal because it suits the natural human stride. A good check is that rise plus run totals 17 to 18 inches. Staying near these figures produces stairs that feel comfortable to almost everyone.
What is the maximum riser height by code?
Under the International Residential Code, the maximum riser height for residential stairs is 7 3/4 inches, and the minimum tread depth is 10 inches. The variation between the tallest and shortest riser in a flight cannot exceed 3/8 of an inch. Always confirm your local code, which may be stricter.
How do I calculate the number of stairs I need?
Divide the total floor-to-floor rise by a comfortable target rise of about 7 inches, then round to the nearest whole number to get the number of steps. Divide the total rise back by that whole number to find the exact, equal rise per step. Every riser must be this same height.
Why is the bottom step of a stringer cut shorter?
Because the tread material adds thickness on top of every step. If the bottom riser were left full height, the finished first step would be too tall once the tread sits on it. Subtracting one tread thickness from the bottom, known as dropping the stringer, keeps all finished steps equal.
How many treads are in a staircase with 14 risers?
Thirteen. A staircase always has one fewer tread than risers, because the top riser delivers you onto the landing or upper floor, which is not a cut tread. So 14 risers means 13 treads. Remembering this prevents miscounting materials and the total run.
What is total run and why does it matter?
Total run is the full horizontal distance the staircase covers, equal to the number of treads multiplied by the run per step. It matters because it tells you how far the stairs project from the upper level, which determines where the bottom landing or footings go and whether the stairs fit the available space.