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Stair calculator

Stairs are a division problem that codes care about. You start with total rise (finished floor to finished floor), pick a target riser height, and back into how many steps and how much horizontal run you need. This page is for planning stringers and rough openings. It is not an engineer stamp and it does not replace your local IRC/local amendments.

in
in
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ORDER ESTIMATESTAIRS
Risers14
Actual riser7.50 in
Treads13
Total run136.5 in
How it calculates
riser count ≈ round(total rise ÷ target riser); actual riser = rise ÷ count; treads ≈ count − 1; total run = treads × tread depth. Confirm local code.

Planning estimate only — not a code stamp. Verify local riser/tread limits.

When to use

Deck stairs shopping; basement stair rebuild planning; checking whether a stair run fits the space before you cut stringers.

When not to

Spiral stairs, winders, and commercial egress — special rules. Final inspection dimensions — measure what you built, do not argue with an inspector using a browser.

Assumptions

You enter total rise and a target riser (or let the tool suggest a count that lands near 7–7.75 in typical residential targets). Tread depth default is a planning value you can edit. Codes vary — confirm locally.

Worked examples

Example 1

total rise 105 in, target riser 7.5 in
→ 14 risers → actual 7.5 in; 13 treads; run depends on tread depth (e.g. 10.5 in → 136.5 in run)

Headroom and landing depth are separate checks.

Example 2

total rise 56 in (short deck), target 7 in
→ 8 risers → 7.0 in; 7 treads

Short flights still need consistent risers — do not fudge the bottom step.

How it calculates

Divide total rise by a target riser, recompute exact riser height, then project run from tread depth.

  1. Measure finished-floor to finished-floor rise in inches.
  2. Enter a target riser near 7–7.75 in (or your local max).
  3. Set tread depth; read riser count, actual riser, treads, and total run.
riser count ≈ round(total_rise ÷ target_riser)
actual riser = total_rise ÷ riser_count
treads ≈ riser_count − 1
total run ≈ treads × tread_depth

Common traps

  1. Finished floor thickness — forget flooring and every riser is short.
  2. Riser count vs tread count — off-by-one is the classic DIY cut mistake.
  3. Codes differ on max riser / min tread — our defaults are planning aids.
  4. Open risers / nosing change comfort, not the basic division.

Next tool

Stringer length focused → stair stringer calculator.

Deck framing around the stair → deck calculator.

FAQ

Divide total rise by a legal riser height and round to a whole number of risers, then recompute exact riser height.

Related

Estimate only — not a contractor bid or engineered takeoff. Confirm bag yields and local codes before you pour or order.