Stair Rise and Run: What the Code Allows, and What Your Staircase Actually Needs

The question people ask, and the question they need answered

Search for stair rise and run and you get a limit: 7-3/4 inches. It is the right number and it answers the wrong question, because nobody builds a staircase by picking a riser height.

What you have is a hole in a floor and a distance to climb. What you need is how many risers go in that distance, how tall each one ends up, and how much floor the finished stair is going to eat. The limit is a constraint on that arithmetic, not the answer to it.

The first chart above does the arithmetic for the heights that actually come up. The rest of this page is what the chart cannot say in a cell.

If someone told you 7 and 11, they were reading the wrong code

This is the single most common piece of bad stair advice, and it is bad in an interesting way: the numbers are real, they are just from the book that governs offices and shops.

• IBC 1011.5.2, the general commercial rule: 7 inch maximum riser, 11 inch minimum tread.
• IRC R311.7.5.1 and R311.7.5.2, for houses: 7-3/4 inch maximum riser, 10 inch minimum tread.

Here is the part that almost every summary drops. The IBC does not actually disagree with the IRC about houses. Its own exception 3 to that section says that in Group R-3 occupancies and within dwelling units in Group R-2, the maximum riser is 7-3/4 and the minimum tread is 10 — the residential numbers, written into the commercial code.

So for a house the two codes say the same thing. What conflicts is not the codes but the articles about them, which quote the headline figure and skip the exception. If your inspector is looking at a single-family home, 7-3/4 and 10 is the standard being applied.

How the riser height is actually decided

Three steps, no judgement involved:

1. Measure the total rise, finished floor to finished floor. Not subfloor. If tile or hardwood is going down later, it belongs in this number now.
2. Divide by 7.75 and round up. That gives the fewest risers that stay legal. A 105 inch rise divides to 13.5, so you need 14.
3. Divide the total rise by that riser count. 105 ÷ 14 = 7.5 inches per riser. Done.

Want a gentler stair? Add a riser and divide again — 105 ÷ 15 gives 7 inches. The code only sets a ceiling, so going down is always allowed. It just costs you 10 inches of floor for every riser you add.

Your riser height will not be a round number, and that is fine

Of the twelve floor heights in the chart, only half land on a clean sixteenth of an inch. A 96 inch rise gives 7.385 inches per riser. An 84 inch basement gives 7.636.

People find this unsettling and start rounding, which is exactly the wrong instinct. The code does not care what the number is. It cares that all of them are the same. Riser heights within a flight may vary by no more than 3/8 inch between the tallest and the shortest, and tread depths get the same 3/8 inch limit.

Rounding is not harmless, either. Take the 126 inch rise: 17 risers at 7.412 inches, which reads as 7-7/16. Stack seventeen of those rounded risers and you land at 126.44 — nearly half an inch past your floor. The sixteenths in the chart are there so you can picture the step, not so you can multiply them. Lay the true division out on a story pole and mark all seventeen from it, and the remainder vanishes into the marks instead of accumulating at the top.

That tolerance sounds generous until you see what eats it:

• The bottom riser. Cut the stringer without allowing for the tread thickness and the first step comes out a full tread thicker than the rest. This is the classic failure, and it usually blows the 3/8 on its own.
• Finished floor at one end only. Frame to subfloor at the top and finished floor at the bottom and every riser is off by the thickness of the flooring.
• Carpet. The code says dimensions are measured exclusive of carpets, rugs and runners, so a thick pad does not fix a short riser. It also does not create a violation where there was not one.

A stair that trips people trips them on the odd step, which is why the uniformity rule exists and why it is enforced more keenly than the maximum.

Treads are always one fewer than risers

The last riser lifts you onto the upper floor, and that floor is the final tread. So fourteen risers means thirteen treads.

That subtraction is where staircases stop fitting. Thirteen treads at 10 inches is 130 inches of floor — just under eleven feet, before you add the landing at the bottom. Going to an 11 inch tread for comfort adds another thirteen inches. If the opening in the floor above was framed for something shorter, that is the moment you find out.

Two related limits worth knowing before you draw anything:

• Headroom is 6 feet 8 inches, measured plumb from a line joining the tread nosings. This is what usually forces the floor opening to be longer than people expect.
• A single flight may not rise more than 12 feet 7 inches without a landing. Rare between two storeys, easy to hit in a tall basement.

The comfort formulas, and why the legal minimum is not a good stair

Carpenters check three old rules to see whether a stair will feel right:

• rise + run should land between 17 and 18
• 2 × rise + run should land between 24 and 25
• rise × run should land between 71 and 75

None of them is code. None is enforceable. But run them and something useful falls out.

A stair built exactly to the residential limits — 7-3/4 riser on a 10 inch tread — passes the first rule and fails the other two. The legal minimum staircase is legal, and it is steep. It is what you build when the floor space genuinely is not there.

Now look at what the arithmetic actually handed you a few sections ago. A standard 105 inch floor-to-floor gives 7-1/2 inch risers, and on a 10 inch tread that combination scores 17-1/2, 25 and 75. It passes all three.

That is the quietly reassuring part of this page. The stair you get by dividing properly is not the code minimum and is not a compromise — it is, by the trade's own three-hundred-year-old measures, a good staircase. You get there by measuring the total rise and dividing it honestly, which is the only thing this page has been asking you to do.

The one worth avoiding is the opposite corner: a 7-3/4 riser on an 11 inch tread fails all three, and manages to be both steep and long.

Before you cut a stringer

Measure the total rise in three places across the opening and use the largest. Frame to finished floor at both ends, or write down exactly what is going down later and subtract it. Then check your riser count against the floor opening you actually have, not the one on the drawing.

And do the last check with a tape rather than a calculator: mark out the run on the floor and stand at the bottom of it. Eleven feet of staircase looks very different on a floor than it does in a spreadsheet.