Stair Rise & Run Calculator

How this is calculated

The number of risers is the total rise divided by your maximum allowable riser height, rounded UP - because every riser has to come in at or under that limit. The actual riser height is then the total rise divided by that number of risers, which is what you build to. ⚠️ EVERY RISER MUST BE THE SAME HEIGHT. This is the single most important thing on the page and it is a safety requirement rather than a preference. People climb stairs by rhythm rather than by looking, so a riser that differs from its neighbours by even a fraction of an inch is a trip hazard - and codes typically limit the variation between the largest and smallest riser in a flight to something like three eighths of an inch across the whole run. That is why you divide the rise by a whole number of risers rather than making the last one fit. There is always one fewer TREAD than riser. The top riser lands on the floor above, which serves as the final tread - so a 14-riser staircase has 13 treads. Getting this wrong by one is the classic error and it shows up as a staircase that is a full tread too long or too short. The total run is the tread count times the tread depth. On the default figures that is 130 inches - nearly eleven feet of floor space, at both the top and bottom. It is very often the constraint that decides where a staircase can go, and it is almost always larger than people expect before they work it out. Total rise means FINISHED floor to FINISHED floor. Measuring to a subfloor and then laying flooring afterwards changes the top and bottom risers by the thickness of the finish, which is exactly the sort of error the equal-riser rule cannot tolerate. ⚠️ THE LIMITS ARE CODE, NOT ARITHMETIC. Maximum riser height, minimum tread depth, minimum headroom, handrail requirements and landing rules all vary by jurisdiction and by whether the stair is in a dwelling, a commercial building or a loft conversion. The defaults here are common residential figures, not permission. Look yours up. The rules of thumb - riser plus tread around 17 to 18 inches, or twice the riser plus the tread around 24 to 25 - describe stairs that feel comfortable underfoot. They are guidance about comfort layered on top of the code limits, not a substitute for them.

Common questions

Why must every riser be identical?

Because people climb stairs by rhythm, not by looking. After the first two steps your body predicts where the next tread will be, and a riser that differs from its neighbours breaks that prediction at the moment your weight is already committed. It is one of the most common causes of falls on stairs, which is why codes typically limit the variation across an entire flight to a fraction of an inch. It is also why you divide the total rise by a whole number of risers rather than letting the last one take up the remainder.

Why is there one fewer tread than riser?

Because the top riser brings you level with the floor above, and that floor is the final surface you step onto - so it does the job of the last tread. A 14-riser staircase has 13 treads. Getting this off by one is the classic stair error, and it produces a staircase a whole tread too long or too short, which is not something you can adjust afterwards.

Why does the total run matter so much?

Because it is usually the constraint that decides whether a staircase fits at all, and it is nearly always bigger than people picture. The default figures here need almost eleven feet of floor, and you need clear space at the top and bottom as well. Working the run out early is what stops a design being drawn twice - it is far more often the run than the rise that forces a rethink.

What counts as the total rise?

FINISHED floor to FINISHED floor. If you measure to a subfloor and then lay flooring afterwards, the top and bottom risers change by the thickness of that finish - and since the whole flight has to be within a fraction of an inch, that is exactly the sort of error the equal-riser rule cannot absorb. Decide your floor finishes before you cut a stringer.

Are the default numbers the code?

No. They are common residential figures and nothing more. Maximum riser height, minimum tread depth, minimum headroom, handrail requirements and landing rules all vary by jurisdiction, and they differ again between a dwelling, a commercial building and a loft conversion. Stairs are one of the most heavily regulated parts of a building precisely because of how people are injured on them. Look your own figures up before building.

What are the rise-and-run rules of thumb for?

Comfort, layered on top of the code limits rather than replacing them. Riser plus tread around 17 to 18 inches, or twice the riser plus the tread around 24 to 25, both describe stairs that feel natural to walk. A staircase can satisfy every code requirement and still feel wrong underfoot, and these are what that difference tends to come down to.

Take it further with AI

Copy this into ChatGPT or Claude with your own numbers filled in. It hands over the figures this calculator worked out, so the answer is built on real arithmetic instead of a guess.

I used the Stair Rise & Run Calculator at https://www.bfcbrilliance.com/tools/stair-calculator.

What I entered:
- Total rise (finished floor to finished floor) (in): ___
- Maximum riser height allowed (in): ___
- Tread depth (in): ___

What it calculated:
- Number of risers: ___
- Actual riser height: ___
- Number of treads: ___
- Total run: ___
- — in feet: ___

Use those figures as given — they are already worked out, so please don't recalculate or estimate your own. Help me turn them into a plan: what to buy or do, in what order, roughly what it should cost, and the mistakes people most often make with this job.

Where the job touches structure, gas, or electrics, tell me to check local building code and whether a permit or a licensed trade is required.

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