# Stair Calculator

Canonical URL: https://www.simplywise.com/blog/stair-calculator/
Plain text: https://www.simplywise.com/blog/stair-calculator/llms.txt
Publisher: SimplyWise, Inc. (https://www.simplywise.com)
Published: September 15, 2026
Updated: October 27, 2026
Summary: A stair calculator that turns total rise into riser count, riser height, total run, stringer length, a cut list, and a pass or fail against stair code.

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## Stair Calculator: Risers, Run, Stringer, and Code

Stairs start with one number: total rise, floor to floor. Set it below and the risers, run, stringer, and code check update as you type.

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### Rise, run, stringer, and a code check

Total rise, floor to floor (in)

Desired riser height (in) IRC R311.7.5.1 caps a riser at 7 3/4 in

Tread depth (in)

IRC R311.7.5.2 floor is 10 in. Custom depth below.

Stair width (in)

Nosing (in)

Headroom (in)

7.27 in per riser, over 15 risers

Treads14 treads at 10.5 in

Total run147 in (12 ft 3 in)

Stringer length183 in (15 ft 3 in)

Stringers3 at 2×12, 18 in on center max

Cut list15 rise cuts at 7.27 in, 14 run cuts at 9.5 in

Code checkPass on riser, tread, width, headroom, nosing

Riser, tread, width, headroom and nosing check against IRC stair limits in free municipal handouts. The landing flag is the American Wood Council deck guide rule for exterior stairs, stricter than the code limit on vertical rise. Read September 11, 2026. Local amendments vary.

Risers

Labor $ per riser

Materials $ per riser

$0 before markup

Labor$0

Materials$0

Defaults: a SimplyWise Cost Estimator run, October 13, 2026, a 15-riser, 36 in wide pine stair, old stair removed: $2,100.00 labor, $329.08 materials.

At a glance

1. Risers = total rise divided by your target riser, rounded to whole.
2. Riser height = total rise divided by that count.
3. Treads = risers minus one.
4. Run = treads times tread depth. Stringer = square root of rise squared plus run squared.
5. Code: riser 7 3/4 in max, tread 10 in min, 3/8 in variation, 36 in wide, 6 ft 8 in headroom.
6. A 109 in rise at 7.5 in gives 15 risers at 7.27 in, 147 in of run, 183 in of stringer.

## How the stair calculator works

A stair calculator divides total rise by riser height: 109 in gives 15 risers at 7.27 in. Total rise runs finished floor to finished floor and never bends.

Divide total rise by your target riser and round to a whole count. Divide the rise by that count again for the height you cut. Rounding the height instead fails inspection.

## Stair calculator worked example: 109 inches of total rise

At a 7.5 in target, 109 over 7.5 is 14.53, rounding to 15 risers. Divide back: 109 over 15 is 7.27 in per riser, under the 7 3/4 in cap.

Fifteen risers means 14 treads. At 10.5 in each the run is 147 in, or 12 ft 3 in. The stringer is the square root of 109 squared plus 147 squared: 183 in, so a 16 ft 2×12 cuts one.

## Stair calculator results for common floor heights

Target riser 7.5 in, tread 10.5 in.

| Total rise | Risers | Riser height | Total run | Stringer |
| --- | --- | --- | --- | --- |
| 108 in | 14 | 7.71 in | 136.5 in | 174.06 in |
| 109 in | 15 | 7.27 in | 147 in | 183 in |
| 120 in | 16 | 7.5 in | 157.5 in | 198.01 in |

One inch, 108 to 109, adds a whole riser and 10.5 in of run.

## What the stair code actually says

These limits come from the residential code stair sections in free municipal handouts. A riser tops out at 7 3/4 in and a tread runs 10 in minimum, nosing to nosing. Neither may vary by more than 3/8 in.

The stair is 36 in wide minimum, with 6 ft 8 in of headroom above the nosing line. Headroom catches remodels, where the opening above is already framed.

On solid risers, nosing projects 3/4 in to 1-1/4 in; at 11 in treads it is not required. It adds nothing to the run, so subtract it from tread depth when you mark the stringer.

## Turn the layout into a signed quote

The stair calculator gives the framing; the customer wants a number. SimplyWise Cost Estimator (https://www.simplywise.com/cost-estimator) turns a photo into an itemized estimate in about 6 seconds. Pricing is $29.99/mo or $239.99/yr, about $20/mo on annual, with a 7-day trial.

## Cutting the stringer

For exterior stairs the American Wood Council deck guide is prescriptive: stringers are 2×12 minimum, a cut stringer stair needs three, and spacing tops out at 18 in on center. A 60 in stair takes five.

The same guide requires an intermediate landing once stairway height passes 12 ft on an exterior stair. Interior code allows 151 in between floors or landings, 147 in in older editions. The stair calculator holds the stricter 12 ft line, so a 150 in rise reads as a landing job.

## Lay the stairs out in this order

1. Measure total rise on finished surfaces Floor to floor, finish included. Forgotten 3/4 in hardwood spreads across every riser.
2. Set the count, then the height Round to a whole riser, then divide the rise back by it. Never round the height itself.
3. Check the run against the room Run is treads times tread depth. A deeper tread makes a tight run worse.
4. Confirm headroom before you cut Measure 6 ft 8 in down from the sloped line touching each nosing. The opening above is costly to move.

## Keep reading

- Construction Calculators: the full set (https://www.simplywise.com/blog/construction-calculators/)
- Concrete Slab Cost Calculator (https://www.simplywise.com/blog/concrete-slab-cost-calculator/)
- Drywall Sheet and Mud Calculator (https://www.simplywise.com/blog/drywall-sheet-and-mud-calculator/)
- Framing Calculator (https://www.simplywise.com/blog/framing-stud-calculator/)

## Sources

### Stair code limits

- County of Placer, 210 Residential Stairs handout (https://www.placer.ca.gov/DocumentCenter/View/3303/Residential-Stairs-PDF) (R311.7.1 width 36 in; R311.7.2 headroom 6 ft 8 in; R311.7.5.1 riser 7 3/4 in; R311.7.5.2 tread 10 in; 3/8 in variation; R311.7.5.3 nosing 3/4 in to 1-1/4 in; read 2026-09-11).
- City of Spearfish, Residential Deck Handout, 2021 IRC (https://www.spearfish.gov/DocumentCenter/View/5233/Residential-Deck-handout-PDF) (second source, same riser, tread, width and variation limits; read 2026-09-11).

### Stringer and landing rules

- American Wood Council, DCA 6 Prescriptive Residential Wood Deck Construction Guide (https://awc.org/wp-content/uploads/2022/02/AWC-DCA62012-DeckGuide-1405.pdf) (stringers 2×12 minimum; three cut stringers; 18 in on center max; landing above 12 ft; read 2026-09-11).

### Product

- SimplyWise Cost Estimator, App Store (https://apps.apple.com/us/app/simplywise-cost-estimator/id6670619664) (4.8 rating; verified 2026-09-09).

## Common questions on stairs

### Rise and run

**How many stairs do I need?**

Divide total rise by your target riser height and round to the nearest whole number. A 109 in rise at a 7.5 in target is 14.53, so 15 risers.

**How many treads for 15 risers?**

Fourteen. A stair landing on a floor has one fewer tread than risers, because the upper floor serves as the last tread.

**How much space does a staircase need?**

Run is treads times tread depth. Fifteen risers at 10.5 in is 147 in, or 12 ft 3 in, plus landings.

### Stringers and code

**How do I calculate stringer length?**

Square root of total rise squared plus total run squared. For 109 in of rise and 147 in of run that is 183 in, so a 16 ft 2×12 cuts one.

**What is the maximum riser height allowed?**

7 3/4 in, with a 10 in minimum tread, per the code sections published in municipal handouts. The greatest riser cannot beat the smallest by more than 3/8 in.

**Can SimplyWise price a stair build from a photo?**

Yes. SimplyWise Cost Estimator turns a photo into an itemized estimate in about 6 seconds, with material and labor line items. Free to try, $29.99/mo or $239.99/yr.

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## About SimplyWise

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