Stair Calculator
Enter the total rise and this tool divides it into equal risers under the common IRC maximum, then reports the exact riser height (snapped to the nearest 1/16 in for the tape), total run, stringer length, and stair angle — with the geometry checked against widely adopted code figures.
Total rise and layout options
Example: a 105 in rise → 14 risers at 7 1/2" over a 130 in run.
Quantity and geometry estimates only — this tool determines no structural adequacy, code compliance, or engineering. Stringer sizing, guards, handrails, and headroom need a licensed professional; verify dimensions and local code before you cut.
How the layout is computed
The riser count is the smallest number of equal risers that keeps each one at or under the
limit: ⌈rise ÷ max riser⌉. The worked flight: a 105 in rise ÷ the common
7.75 in maximum needs 14 risers, and 105 ÷ 14 puts each at exactly 7.5 in (7 1/2"). A flight always has one fewer tread than risers, so 13
treads at 10 in give a total run of 130 in. The stringer hypotenuse is √(rise² + run²) = 167.11 in and
the flight climbs at 38.9°.
When the exact riser height does not land on a tape-measure sixteenth, the tool shows the nearest 1/16 and says so — the small remainder is absorbed across the flight the same way carpenters split an odd sixteenth during layout.
The common IRC figures this tool checks
| Rule | Common IRC figure | Section |
|---|---|---|
| Maximum riser height | 7.75 in (196 mm) | R311.7.5.1 |
| Minimum tread depth | 10 in (254 mm) | R311.7.5.2 |
| Riser variation within a flight | ≤ 0.375 in (3/8 in) | R311.7.5.1 |
| Minimum headroom | 80 in (6 ft 8 in) | R311.7.2 |
These are common IRC values — local codes vary. They come from the 2018 International Residential Code as published by the ICC and quoted verbatim in municipal handouts; jurisdictions amend riser and tread limits regularly, so treat the flags as a heads-up, never as approval. The equal-riser layout this tool produces addresses the variation rule by construction, and headroom must be checked on site against the 6 ft 8 in figure along the entire flight.
Printing the layout
With your numbers on screen, the Print this layout button strips the navigation and sidebar so the riser height, run, stringer length, and angle print on one sheet — tape it to the stringer stock. Mark riser and tread with a framing square set to the riser height and tread run, and step it off once per riser. The Feet & Inches Calculator chains the tape-measure additions when you lay out landings.
Frequently asked questions
How do I measure the total rise?
Measure vertically from the finished floor at the bottom of the flight to the finished floor at the top, keeping the tape plumb. If the upper finish floor is not installed yet, measure to the subfloor and enter the finish thickness in the optional field so the tool works from the finished surface.
Why does the tool divide the rise into equal risers?
Because uneven steps trip people, model codes limit the riser variation within a flight (commonly 3/8 in between the tallest and shortest). Dividing the total rise by the riser count gives every step an identical height, which is how stringers are laid out in practice.
What are the common code limits for stairs?
The 2018 International Residential Code lists a maximum riser of 7 3/4 inches (R311.7.5.1), a minimum tread depth of 10 inches (R311.7.5.2), and a minimum headroom of 6 ft 8 in (R311.7.2). These are widely adopted values, but states and municipalities amend them — some jurisdictions use 7 in or 8 1/4 in risers — so always confirm with your local building department.
Is the stringer length the board length I should buy?
No — it is the geometric hypotenuse from the first rise to the last. Buy stock longer than the stringer figure so there is material for the top and bottom cuts, the attachment at the header, and layout waste. A 14-riser flight with a 167 in hypotenuse is typically cut from a 16 ft 2×12.
Does this tool check code compliance?
No. It flags geometry against commonly adopted IRC figures as a convenience, and it computes no structure at all — stringer sizing, attachment, guards, handrails, landings, and headroom all need a professional and a local permit review.
Related tools: the Board Foot Calculator totals the stringer and tread lumber, the Feet & Inches Calculator handles the fraction arithmetic, and the Construction Unit Converter moves any figure between imperial and metric.
Stair figures are computed locally and never transmitted. Formulas, IRC sources, and the shared pipeline are documented on the methodology page.