Stair Calculator: Stringer Length, Rise, Run & Code

Q: What is the maximum height for a stair riser?

IRC 2024 caps residential risers at 7.75" (196mm). OSHA allows 9.5" for commercial; ADA accessible stairs max at 7". The calculator checks your design against IRC, OSHA, or ADA—pick your code.

Q: How do you calculate stringer length?

Stringer length uses the Pythagorean theorem: Stringer=Rise2+Run2Stringer = ^2 + Run^2Stringer=Rise2+Run2. Example: 108" rise and 120" run ≈ 161.5" (13.5 ft). Add 6-12" to lumber for cutting waste.

Q: What is the minimum headroom for stairs?

The IRC requires a minimum headroom of 80 inches (6'8") measured vertically from the stair nosing to the ceiling above. This clearance must be maintained for the entire length of the stairway. Commercial OSHA standards require 84 inches minimum.

Q: What is the 7-11 rule for stairs?

The 7-11 Rule: 2×Rise+Run≈24–25 in2 × Rise + Run 24--25 in2×Rise+Run≈24–25 in for optimal ergonomics—roughly 7" rise and 11" run. The calculator checks this against your design.

Q: How do I calculate stairs for a 10-foot rise?

For a 10-ft (120") rise with 7.5" steps: 120 ÷ 7.5 = 16 risers, 15 treads. At 10" per tread, total run = 150" (12.5 ft). The calculator tunes rise and run for code compliance.

Q: What is the difference between IRC and OSHA stair requirements?

IRC (residential): max 7.75" rise, min 10" run. OSHA (commercial): max 9.5" rise, min 9.5" run—steeper because workers use handrails. ADA (accessible): max 7" rise, min 11" run. The calculator supports all three.

Stair Engineering Intelligence: From Blueprint to Build

Professional stair construction requires precise mathematics and code compliance. This tool handles the complex calculations so you can focus on building.

Tool Capabilities

Dual Calculation Modes

•Choose "Fixed Step Height" to set your preferred rise (e.g., 7.5"), or "Fixed Number of Steps" to specify the count and let the tool calculate optimal dimensions.

•Both modes validate against your selected building code in real-time.

Master Carpenter Features

•Toggle to Master Mode for advanced inputs: tread thickness, floor thickness, and headroom clearance.

•Flush mount vs. standard stringer options adjust calculations automatically.

Multi-Code Validation

•Instant compliance checking against IRC 2024 (residential), OSHA (commercial), or ADA (accessible) standards.

•Orange warnings and red errors flag violations before you cut lumber.

Contractor-Ready Output

•Copy a complete blueprint with one click: stringer length, miter saw angle, rise/run, and compliance status.

•Fraction toggle displays measurements as 7 1/4" for direct tape measure transfer.

Stair Calculator: Stringer Length, Rise, Run & Code Compliance

Free professional stair calculator. Calculate stringer length, riser height, tread depth, and angle of inclination. IRC 2024, OSHA, and ADA code validation built-in.

Complete Stair Calculation Guide

Understanding Stair Geometry

Total Rise:

The vertical distance from the lower floor surface to the upper floor surface. This is your starting point for all calculations. Measure precisely—even 1/4" error multiplies across all risers.
Total Run:

The horizontal distance the staircase covers, measured from the face of the first riser to the face of the last riser. This determines how much floor space your stairs consume.
Stringer Length:

The board length for the angled supports. Formula: $\sqrt{\text{Rise}^2 + \text{Run}^2}$ . Buy lumber 12-18" longer for waste.

Every staircase is built on three fundamental measurements that determine safety, comfort, and code compliance.

IRC 2024 vs OSHA vs ADA Requirements

IRC 2024 (Residential):

Maximum riser height: 7.75". Minimum tread depth: 10". Minimum headroom: 80". Applies to single-family homes and townhouses.
OSHA (Commercial/Industrial):

Maximum riser height: 9.5". Minimum tread depth: 9.5". Minimum headroom: 84". Used in factories, warehouses, and commercial buildings.
ADA (Accessible):

Maximum riser height: 7". Minimum tread depth: 11". Required for public buildings and spaces requiring wheelchair accessibility nearby.

Different building codes apply to different construction types. Using the wrong standard can result in failed inspections.

The Mathematics of Safe Stairs

Essential Formulas for Stair Construction

Riser Height:

Rise = Total Rise ÷ Number of Risers
Aim for 7-7.5" for residential stairs. Never exceed 7.75" per IRC code.
Tread Depth:

Run = Total Run ÷ (Number of Risers - 1)
Minimum 10" for residential. Note: You have one fewer tread than risers.
Stringer Length:

Stringer = √(Total Rise² + Total Run²)
Pythagorean theorem. This is the hypotenuse of your stair triangle.
Angle of Inclination:

Angle = arctan(Total Rise ÷ Total Run)
Ideal range: 30°-37°. Steeper than 37° feels uncomfortable; shallower than 30° wastes space.

These formulas have been refined over centuries to create stairs that are safe, comfortable, and code-compliant.

Pro Tips: Stair Construction Best Practices

Contractor-Level Accuracy

Measure Twice, Cut Once:

Verify total rise at both ends of the stair opening. Floors are rarely perfectly level—use the larger measurement and adjust the bottom riser.
Account for Flooring:

If the upper floor has carpet (3/4") and lower floor is hardwood (3/4"), subtract this difference from your first riser. This maintains consistent rise after flooring is installed.
The First Riser Rule:

The first riser is always shorter by the tread thickness (typically 1-1/8"). This compensates for the tread you'll add on top, keeping all rises equal after installation.
Stringer Layout:

Use a framing square with stair gauges. Mark the rise on one leg, run on the other. Trace the pattern consistently, cutting with a circular saw and finishing corners with a jigsaw.

Professional stair builders follow these practices to ensure perfect results every time.

FAQ

? What is the maximum height for a stair riser?

IRC 2024 caps residential risers at 7.75" (196mm). OSHA allows 9.5" for commercial; ADA accessible stairs max at 7". The calculator checks your design against IRC, OSHA, or ADA—pick your code.

? How do you calculate stringer length?

Stringer length uses the Pythagorean theorem:

\text{Stringer} = \sqrt{\text{Rise}^2 + \text{Run}^2}

. Example: 108" rise and 120" run ≈ 161.5" (13.5 ft). Add 6-12" to lumber for cutting waste.

? What is the minimum headroom for stairs?

The IRC requires a minimum headroom of 80 inches (6'8") measured vertically from the stair nosing to the ceiling above. This clearance must be maintained for the entire length of the stairway. Commercial OSHA standards require 84 inches minimum.

? What is the 7-11 rule for stairs?

The 7-11 Rule:

2 \times \text{Rise} + \text{Run} \approx 24\text{--}25\text{ in}

for optimal ergonomics—roughly 7" rise and 11" run. The calculator checks this against your design.

? How do I calculate stairs for a 10-foot rise?

For a 10-ft (120") rise with 7.5" steps: 120 ÷ 7.5 = 16 risers, 15 treads. At 10" per tread, total run = 150" (12.5 ft). The calculator tunes rise and run for code compliance.

? What is the difference between IRC and OSHA stair requirements?

IRC (residential): max 7.75" rise, min 10" run. OSHA (commercial): max 9.5" rise, min 9.5" run—steeper because workers use handrails. ADA (accessible): max 7" rise, min 11" run. The calculator supports all three.

Stair Calculator: Stringer, Rise, Run & Code Compliance

Stair Configuration

Construction Manifest