Stair Stringer Calculator

A stair stringer is the diagonal support board that runs the length of a staircase — and cutting it correctly requires precise measurements before you touch a saw. Enter your total rise, tread depth, number of steps, tread thickness, stringer width, and stringer attachment type into the Stair Stringer Calculator to get the required stringer length. Secondary outputs include step rise, total run, stringer angle, and a code compliance check.

inches

Vertical height from bottom to top of stairs

inches

Horizontal depth of each step

Total number of steps in the staircase

inches

Thickness of the tread board

inches

Width of the stringer board (2x12 = 11.25")

Results

Stringer Length

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Step Rise (Height)

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Stringer Angle

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Total Run

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Code Compliant

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Results Table

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Frequently Asked Questions

What is the standard rise and run for stairs?

The standard rise (step height) is typically 7-7.75 inches, and the standard run (tread depth) is 10-11 inches. The sum of rise + run should equal 17-18 inches for comfortable stairs.

How do I calculate stringer length?

Stringer length is calculated using the Pythagorean theorem: √(total rise² + total run²). This gives you the diagonal length needed for the stair stringer board.

What angle should my stair stringers be?

Stair stringers typically have an angle between 30-40 degrees from horizontal. Angles between 32-35 degrees are most comfortable for regular use.

How many stringers do I need for my stairs?

For stairs up to 30 inches wide, use 2 stringers. For stairs 30-48 inches wide, use 3 stringers. Add one stringer for every additional 16 inches of width.

Are there building codes for stair dimensions?

Yes, most building codes require: maximum rise of 7.75 inches, minimum run of 10 inches, and consistent rise/run throughout the staircase. Check your local codes for specific requirements.

What's the difference between outside frame and flush frame attachment?

Outside frame attachment mounts stringers to the outside of the frame, while flush frame attachment sits the stringers inside or flush with the frame structure.

Can I use this calculator for deck stairs?

Yes, this calculator works for both interior and exterior stairs including deck stairs. Just ensure your measurements account for any deck height and local building codes.

What size lumber should I use for stringers?

Use 2x12 lumber for most residential stairs as it provides adequate depth for proper notching. For longer spans or heavy loads, consider engineered lumber or consult a structural engineer.