Staircase Calculator — IRC R311.7

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Enter total rise to calculate

Stair Parameters

Total Rise (inches)

Target Riser Height (in)

Tread Depth (inches)

in (min 10" per IRC)

Stair Width (inches)

Nosing (inches)

Available Headroom (inches)

Number of Stringers

Results

Actual Riser Height

inches per step

Risers

Treads

Total Run

Angle

Stringer Length --

-- Riser Height 4"–7.75"

-- Tread Depth min 10"

-- Nosing 0.75"–1.25"

-- Headroom min 80"

Side Profile

Riser Height Distribution

Shows each riser vs. IRC limits at a glance.

Actual Riser Max (7.75") Min (4")

Stair Geometry Summary

Price Inputs (per linear foot)

2×12 Stringer Lumber ($/LF)

Tread Board ($/LF)

1×8 Riser Board ($/LF)

Handrail ($/LF)

Handrail — Number of Sides

Materials Estimate

Estimated Total $--

Quantities include 10% waste allowance. Prices are estimates — verify with local supplier.

IRC R311.7 — Stairway Requirements

Parameter	Requirement	Notes
Minimum Width	36 inches	Clear width above handrail; 31.5" min with rail one side, 27" with rails both sides
Maximum Riser Height	7¾ inches (7.75")	Measured vertically between tread nosings
Minimum Riser Height	4 inches	Open risers permitted if opening < 4" sphere cannot pass
Riser Uniformity	±3/8" max variation	Greatest vs. smallest riser in any flight
Minimum Tread Depth	10 inches	Measured horizontally from nosing to nosing
Tread Uniformity	±3/8" max variation	Greatest vs. smallest tread in any flight
Nosing Profile	0.75"–1.25" projection	Radius or bevel on leading edge required; ≤9/16" radius or 60° bevel
Headroom Clearance	6 ft 8 in (80")	Measured vertically from tread nosing to any obstruction
Handrail Height	34"–38"	Measured vertically from tread nosing
Handrail Graspability	Type I or II	Type I: 1.25"–2" OD circular; Type II: non-circular with graspable profile
Handrail Continuity	Full flight length	Must run full length of stair flight; returns or extensions at ends
Guard Height	36 inches min	42" required where floor more than 30" above grade or floor below
Guard Opening Limits	4-inch sphere	Openings in guards must not allow passage of a 4" sphere
Landing — Width	= stair width	At top and bottom of each stairway
Landing — Depth	Min 36 inches	In direction of travel; doors may not reduce below 24"
Winders	Min 10" at 12" from narrow edge	6" min at narrow edge; any tread min 6"

Rule of Thumb Checks

Formula	Ideal Range	Your Values
Rise + Run	17" – 18"	--
2× Rise + Run	24" – 25"	--
Rise × Run	70" – 75" sq.	--
Stair Angle	30° – 35°	--
Total Run / Total Rise	≈ 1.3 – 1.6	--

Source: International Residential Code (IRC) 2021, Section R311.7. Always verify with your local jurisdiction — some jurisdictions adopt earlier editions or have local amendments.

How to Use This Staircase Calculator

Enter Total Rise — Measure floor-to-floor height in inches (e.g., 108" for a 9-foot ceiling). This is the most critical measurement.

Set Target Riser Height — The calculator divides total rise by this to find the closest whole-number riser count, then recalculates the exact riser height.

Choose Tread Depth — Use the chips for common sizes or enter a custom value. IRC requires a minimum of 10 inches.

Check the Compliance Badges — All four badges must show a pass (green) before your design meets IRC R311.7.

Review Stair Profile tab — See riser heights charted against IRC limits, and the full geometry summary.

Get a Materials Estimate — Switch to the Materials tab, enter your local lumber prices, and get a cost estimate with quantities.

Glossary

Rise

Vertical distance from one tread to the next. IRC limits: 4"–7.75" per step.

Run / Tread Depth

Horizontal depth of each step measured from nosing to nosing. IRC minimum: 10".

Nosing

Tread overhang beyond the riser face. IRC requires 0.75"–1.25" on closed-riser stairs.

Stringer

The inclined structural member that supports the treads and risers. Typically 2×12 lumber, notched or solid.

Headroom

Vertical clearance from any tread nosing to any overhead obstruction. IRC minimum: 80" (6'8").

Total Rise

Floor-to-floor vertical distance the stairway must span. Measured from finished floor to finished floor.

Total Run

Horizontal distance consumed by the staircase, equal to (number of treads) × (tread depth).

IRC R311.7

Section of the International Residential Code governing stairways in one- and two-family dwellings.

Frequently Asked Questions

Why does the calculator round to a whole number of risers?

Each riser in a flight must be within 3/8" of the others per IRC R311.7.5.1. Having a non-integer number of risers is physically impossible — you can only have complete steps. The calculator finds the nearest integer that keeps the actual riser height within the 4"–7.75" IRC range.

Why are there always one fewer tread than riser?

The top landing acts as the final "tread." When you step off the last riser you land on the upper floor itself, so the count of physical tread boards is always risers minus one.

What is the 2R + T rule?

A classic ergonomic guideline: twice the riser height plus the tread depth should equal 24–25 inches. This range produces the most comfortable stride length for an average adult. It's not an IRC code requirement but is widely used by experienced carpenters.

Do I need a handrail on both sides?

IRC R311.7.8 requires a handrail on at least one side of every stairway with 4 or more risers. Both sides are required when stair width exceeds 44 inches. Local codes may be stricter.

Can I use open risers?

Yes — IRC R311.7.5.1 permits open risers as long as the opening does not allow passage of a 4-inch sphere. This is typically achieved by keeping the opening to 3.75" or less, or by angling solid treads to close the gap visually without a riser board.

How many stringers do I need?

Most residential stairs use 3 stringers for widths of 36"–48": two outer stringers and one centered. Stairs narrower than 30" sometimes use 2. For widths over 48", add a stringer for every additional 16" of width. Always check local structural requirements.