Stair Rise & Run Calculator

Calculate riser height, tread depth, total run, stair angle, and stringer length from your total rise. Includes an IBC code check to flag non-compliant riser heights before you build.

Need stair stringers, framing tools, or levels for layout? Find them at Express Tools.

Shop Express Tools →

Quick Answer

Number of risers = round(Total Rise ÷ Target riser height). Actual riser = Total Rise ÷ Riser count. Total run = (Riser count − 1) × Tread depth. Stringer length = √(Total Rise² + Total Run²). IBC maximum riser height is 7"; minimum tread depth is 11" for commercial, 10" for residential.

How to Use the Stair Rise & Run Calculator

1. Measure total rise — Measure the total vertical distance from finished floor to finished floor in inches. This is the most important measurement — errors here cascade through every riser. Account for finished floor materials (hardwood, tile, carpet) that will be added after framing.
2. Set target riser height — Enter a target riser height (7" is the most comfortable for most people). The calculator rounds the riser count to a whole number and recalculates the exact riser height to eliminate the fractional remainder. All risers must be equal — a ‟short” or ‟tall” bottom riser is a tripping hazard and a code violation.
3. Enter tread depth — Input the tread depth (run) in inches. This is the horizontal depth of each step, measured from nosing to nosing. IBC requires 11" minimum for commercial; IRC allows 10" for residential.
4. Check the code flag — The calculator checks your riser height against IBC limits and flags it if out of range. Fix the riser count or tread depth until the result is compliant before cutting stringers.

Understanding Stair Geometry

Riser count = round(Total Rise ÷ Target Riser)
Actual Riser = Total Rise ÷ Riser Count
Total Run = (Riser Count − 1) × Tread Depth
Stringer Length = √(Total Rise² + Total Run²)
Stair Angle = atan(Total Rise ÷ Total Run)

Comfort rule (7-11): Riser ≤ 7", Tread ≥ 11"
Riser + Tread comfort target: 17–18"

The stringer is the diagonal structural board that supports the treads. It’s cut from 2×12 stock using a framing square set to the rise and run. The stringer length formula gives you the minimum board length needed — always add 12–18 inches for the top and bottom connections. Note: there are always one fewer tread than risers — the top landing is the last “tread,” so a 12-riser staircase has 11 treads.

IBC and IRC Stair Code Requirements

Requirement	IBC (Commercial)	IRC (Residential)
Max riser height	7"	7-3/4"
Min riser height	4"	4"
Min tread depth	11"	10"
Max riser variation	´3/16"	´3/8"
Min headroom clearance	6'8"	6'8"
Min stair width (1 side handrail)	44"	36"
Handrail height	34–38" above nosing	34–38" above nosing

Always verify with your local AHJ (Authority Having Jurisdiction) — local amendments may be stricter than IBC or IRC minimums.

When to Use This Calculator

▸

Permit drawings and submittals — Calculate all stair geometry before drawing the stair section. Confirm riser height and tread depth are code-compliant. Building departments commonly reject stairs drawn with non-compliant risers even if the contractor “just adjusts it in the field.”

▸

Stringer layout and cutting — Use the calculated riser height and tread depth to set your framing square. Mark the stringer, cut the top and bottom, and confirm the stringer fits before cutting all three. Use a stair gauge to keep the square set consistently.

▸

Retrofit and remodel stairs — When replacing or adding to an existing stair, measure the actual total rise carefully — floors settle, slabs heave, and finish floor materials change the rise. Recalculate the stringer each time rather than assuming the old geometry is still correct.

Document stair inspections with Sitemark →

Log riser measurements, handrail heights, and inspector sign-off with photos. Required by most building departments for certificate of occupancy.

Start free trial

Frequently Asked Questions

What is the standard riser height for stairs?

The International Building Code (IBC) requires risers to be between 4" and 7" for commercial occupancies, and residential codes (IRC) allow up to 7-3/4". Most comfortable stairs use 7" risers. This calculator checks your riser against IBC limits.

What is the minimum tread depth for stairs?

The IBC requires a minimum tread depth of 11" (measured horizontally, nosing to nosing) for commercial stairs. The IRC allows 10" for residential stairs. This calculator uses 10" as the default but lets you adjust.

How do you calculate the number of risers for stairs?

Divide the total rise (floor-to-floor height in inches) by your target riser height. Round to the nearest whole number. Then recalculate the actual riser by dividing total rise by that whole number. This calculator does it automatically.

What is a stringer on a staircase?

A stringer is the diagonal structural board that supports the treads and risers on the sides of a staircase. Stringer length is calculated as the hypotenuse of a right triangle with legs equal to total rise and total run.

What is the 7-11 rule for stairs?

The "7-11 rule" is a common comfort guideline: riser height should not exceed 7" and tread depth should not be less than 11". Many designers target a riser + tread sum of 17–18" for the most comfortable stair geometry.

Related Calculators

Concrete Bag Calculator →Square Footage Calculator →Linear Feet Calculator →Board Feet Calculator →