Stair Dimensions0 IN
= 108.00 in
Measure from the finished upper floor to the finished lower floor. If the flooring is not down yet, add its thickness at the top and subtract it at the bottom, or your last riser will be wrong. Type it any way you like: 8ft 6in, 8' 6" and 8 6 all read as 8.5 ft, and 6 1/2 in the inches box reads as 6.5 in.
target 7 in, tread 10 in
The target riser is only a starting point. The calculator divides your real rise into equal risers near that target, because every riser in the flight has to match.
Set the nosing to 0 for a solid tread with no overhang. Nosing changes how wide you cut the tread board, not the total run. See the nosing section below for why.
Lumber & Cut List Options
Tread thickness is used for the stringer drop: the bottom riser cut is reduced by the thickness of the tread material so that the first step ends up the same height as the rest. Miss this and every stair you build is out by an inch at the bottom.
Side Elevation1:SCALE
Drawn to your real rise and run. The dashed orange line is the stringer.
Your StairsLIVE
Actual riser height
0.00 in
Code CheckREAD THIS
Your locally adopted code governs
The numbers below are the values commonly written into the International Residential Code for one and two family dwellings, and they are the figures most inspectors in the US start from. They are not automatically the rule where you are building. Codes are adopted state by state and city by city, editions differ, and local amendments override the model code. Commercial and multi family stairs follow the IBC instead, which uses different numbers again.
Treat this section as a design check, then confirm every figure with the building department that will inspect the work, before you cut anything.
The Rule That Fails Inspections3/8 IN
The same limit applies to tread depth within a flight. This is the single rule that fails more stair inspections than the maximum riser height does, and it is the reason this calculator divides your rise into equal risers instead of letting you pick a round number.
Why it exists. People climb stairs on autopilot. After two steps your body has learned the rhythm and stops looking. A riser that is half an inch different from the others, almost always the first or the last one, is the classic trip and fall. Codes regulate the variation, not just the size, for that reason.
How builders break it. Someone decides risers will be a neat 7 in, divides the rise, gets a fraction, and quietly makes the bottom riser whatever is left over. On a 108 in rise, 15 risers of 7 in only comes to 105 in, so the bottom step ends up 10 in tall: nearly three inches out and comfortably illegal. The fix is the opposite order of operations. Pick the number of risers first, then let the riser height be whatever the division gives you, even if it is 7.2 in or 6.86 in.
The other way it breaks: the stringer drop. Cut all your riser marks equal and then set the stringer on the floor, and your bottom riser is taller than the rest by the thickness of the tread material, because every other step gets a tread sitting on top of it and the bottom one does not. Cut the bottom of the stringer down by exactly the tread thickness. This calculator does that for you in the cut list.
Finished floor matters. Measuring to a bare subfloor and then laying tile at the top or a 3/4 in hardwood at the bottom changes the top and bottom risers only, which is exactly the variation the rule catches. Measure finished to finished, or account for the flooring at both ends.
Comfort Cross-Check#FEEL
Code tells you what is legal. These two carpenter's rules tell you whether the stair will feel right to walk. They come from stride length, so they are guides rather than requirements, and a stair can pass code and still feel wrong.
Nosing#NOSE
Nosing is the part of the tread that overhangs the riser below it. It gives your foot a bit more landing area than the structure alone provides, and it is the reason a stair with a 10 in tread depth can still take a size 12 boot.
It does not change the total run. Tread depth is measured from the front edge of one tread to the front edge of the next, so the overhang is already counted once and cancels out along the flight. Your total run is treads multiplied by tread depth, whatever the nosing is. What the nosing does change is how wide you cut the board: with a closed riser the tread board is tread depth plus nosing.
Codes typically require a nosing, usually in the range of 3/4 in to 1-1/4 in, when the tread depth is under 11 in, and typically allow no nosing once the tread is 11 in or deeper. Open riser stairs have their own rules about the size of the opening. Check the adopted edition, because these details move around between code versions.
Landings#LAND
A flight cannot run forever. Codes set a limit and require a landing beyond it, but they express the limit as a maximum vertical rise between landings, not as a number of risers, and the exact figure has changed between code editions and is frequently amended locally.
Because of that, this calculator will not tell you the number. Ask the building department that will inspect the job what maximum vertical rise their adopted edition allows between landings, and design the flight to it. A landing also has minimum dimensions of its own, usually tied to the width of the stair, and doors swinging over a landing bring further requirements.
Also worth confirming while you have them on the phone: minimum headroom, handrail height and graspability, guard height on the open side, and whether your stair needs a handrail on one side or both.
Per Step Cut List#CUTS
| Step | Riser cut | Height above lower floor | Run from bottom of flight |
|---|
Lumber To Buy#BUY
Waste allowance
10% covers the normal miscut and a bad board. Go to 15% or 20% if you are cutting stringers for the first time, because a stringer laid out wrong is a whole board gone, and if you are buying a grade with knots you will have to cut around.
Materials Ticket#STAIR
Enter the total rise to build the ticket.
The ticket carries the cut numbers as well as the lumber, so it works as a layout sheet at the saw. Board counts already include your waste allowance.
How This Is CalculatedSHOW WORK
The assumptions, stated
Number of risers = total rise divided by your target riser height, rounded to the nearest whole number. Rounding to the nearest, not up or down, is what keeps the result near the height you asked for. A 108 in rise with a 7 in target gives 108 / 7 = 15.43, which rounds to 15 risers.
Actual riser height = total rise divided by that number of risers. 108 / 15 = 7.20 in. This is the number you cut, not the 7 in you typed. Every riser gets the same figure so the flight passes the consistency rule.
Treads = risers minus one, for the standard flight where the top riser lands you on the upper floor and that floor is the top tread. 15 risers gives 14 treads. If your design has a tread at the top, say a landing platform that is part of the stair, you have one more tread and the run grows by one tread depth.
Total run = treads multiplied by tread depth. 14 x 10 in = 140 in, which is 11 ft 8 in of floor space. This is the number that most often kills a design: people have the headroom and forget the run.
Stringer length = the hypotenuse of a right triangle whose legs are the total rise and the total run, so the square root of rise squared plus run squared. With a 108 in rise and a 140 in run that is the square root of 11,664 + 19,600 = 31,264, which is 176.82 in, or 14 ft 9 in. Buy stock longer than that: the stringer needs material past the top and bottom cuts, and a 2x12 with the notches cut out of it has very little wood left at the back.
What this page does not do. It does not size the stringer for structural load, check your headroom against the framing above, lay out winders or a curved flight, or design the handrail and guard. Those depend on your framing, your span and your adopted code. Use the deck calculator for exterior stairs framed into a deck, and the square footage calculator if you need the floor area the run will consume.
Stair Quick ReferenceSCREENSHOT ME
Total rise to risers, treads and run
| Total rise | Risers | Riser height | Treads | Total run at 10 in | Stringer |
|---|---|---|---|---|---|
| 24 in | 3 | 8.00 in | 2 | 20 in | 31.24 in |
| 36 in | 5 | 7.20 in | 4 | 40 in | 53.81 in |
| 48 in | 7 | 6.86 in | 6 | 60 in | 76.84 in |
| 60 in | 9 | 6.67 in | 8 | 80 in | 100.00 in |
| 72 in | 10 | 7.20 in | 9 | 90 in | 115.26 in |
| 84 in | 12 | 7.00 in | 11 | 110 in | 138.41 in |
| 96 in | 14 | 6.86 in | 13 | 130 in | 161.60 in |
| 102 in | 15 | 6.80 in | 14 | 140 in | 173.22 in |
| 108 in (9 ft) | 15 | 7.20 in | 14 | 140 in | 176.82 in |
| 114 in | 16 | 7.13 in | 15 | 150 in | 188.40 in |
| 120 in (10 ft) | 17 | 7.06 in | 16 | 160 in | 200.00 in |
| 132 in (11 ft) | 19 | 6.95 in | 18 | 180 in | 223.21 in |
| 144 in (12 ft) | 21 | 6.86 in | 20 | 200 in | 246.45 in |
Riser and tread combinations against both comfort rules
| Riser | Tread | 2R + T | R + T | Reads as |
|---|---|---|---|---|
| 6.00 in | 12.00 in | 24.00 | 18.00 | Shallow and generous, both rules met |
| 6.50 in | 11.50 in | 24.50 | 18.00 | Very comfortable, both rules met |
| 7.00 in | 11.00 in | 25.00 | 18.00 | The classic comfortable stair |
| 7.20 in | 10.00 in | 24.40 | 17.20 | Both rules met, code legal, a normal house stair |
| 7.50 in | 10.00 in | 25.00 | 17.50 | At the top of the comfort band |
| 7.75 in | 10.00 in | 25.50 | 17.75 | Legal at the maximum riser, but steep to walk |
| 8.00 in | 9.00 in | 25.00 | 17.00 | Passes the rules of thumb, fails the code limits |
Finish The Job
Stair Calculator FAQ
How many stairs for a 9 foot ceiling?
For a 108 in total rise with a 7 in target you get 15 risers at 7.20 in each and 14 treads. At a 10 in tread depth the total run is 140 in, which is 11 ft 8 in of floor space, and the stringer works out to 176.82 in, or about 14 ft 9 in.
Be careful with the phrase "9 foot ceiling", though. The total rise is finished floor to finished floor, which is the ceiling height plus the depth of the floor structure above it, so a house with 9 ft ceilings usually has a total rise well over 108 in. Measure the real distance rather than assuming.
What is the maximum riser height and minimum tread depth?
The values commonly written into the International Residential Code are a maximum riser of 7.75 in and a minimum tread depth of 10 in, with a minimum headroom of 6 ft 8 in measured vertically from the nosing line. Those are the figures most US residential inspectors work from.
They are not universal. Your state or city adopts a particular edition and can amend it, commercial and multi family stairs follow the IBC with different numbers, and some jurisdictions are noticeably stricter. Confirm with the building department before you cut, not after.
Why do all the risers have to be the same height?
Because people climb stairs without looking. After two steps your body has the rhythm and stops checking, so a single odd riser is a trip hazard in a way that a uniformly steep stair is not. Codes limit the variation: the largest riser in a flight must not exceed the smallest by more than 3/8 in, and the same applies to tread depth.
It is the rule that fails the most stair inspections, and it is almost always broken the same way. Someone decides on a round 7 in riser, divides the total rise, and lets the leftover fall into the bottom step. Do it the other way round: choose the number of risers first, then accept whatever height the division gives you.
How do I calculate stringer length?
Pythagoras on the total rise and the total run. Stringer length is the square root of rise squared plus run squared. For a 108 in rise and a 140 in run: 108 squared is 11,664, 140 squared is 19,600, the sum is 31,264, and the square root of that is 176.82 in, which is 14 ft 9 in.
Buy longer stock than the bare number. You need material beyond the top and bottom cuts, the layout rarely lands neatly on the end of a board, and once the notches are cut a 2x12 has surprisingly little wood left along the back edge. Many builders use a 2x12 and check that at least 3.5 in of solid material remains behind every notch.
Does the nosing change the total run?
No. Tread depth is measured from the front edge of one tread to the front edge of the next, so the overhang appears at every step and cancels out along the flight. Total run stays treads multiplied by tread depth regardless of the nosing.
What the nosing changes is the board. With a closed riser, the tread board you cut is tread depth plus nosing, so a 10 in tread with a 1 in nosing needs an 11 in board. Codes typically require a nosing, commonly 3/4 in to 1-1/4 in, whenever the tread depth is under 11 in, and typically allow none once the tread reaches 11 in.
How many stairs before I need a landing?
The limit is not written as a number of steps. Codes express it as a maximum vertical rise between landings, the figure has moved between code editions, and it is one of the provisions local jurisdictions amend most often.
That is why this calculator does not print a number for it. Call the building department that will inspect the job, ask what maximum vertical rise their adopted edition allows between landings, and design to that. While you have them, ask about the minimum landing dimensions too, because a landing is usually required to be at least as deep as the stair is wide, and a door swinging onto it adds further rules.
What is the stringer drop and why does my bottom step come out wrong?
Because every step except the bottom one gets a tread laid on top of it. If you mark all the risers equal and set the stringer straight on the floor, the bottom riser finishes taller than the rest by exactly the thickness of the tread material, and you have broken the 3/8 in consistency rule on the very first step.
The fix is to drop the stringer: cut the bottom of the stringer down by the tread thickness, so a 1 in tread means the bottom riser cut is 1 in shorter than the layout mark. The cut list on this page shows the dropped figure. If the stair lands on a concrete slab that will later get tile, account for that finish too.