Stair Calculator

The Stair Calculator takes the guesswork out of planning a staircase by calculating the correct rise, run, and stringer dimensions for a safe, code-compliant build. Enter your total height and step run (tread depth), then choose automatic or manual mode and your stringer attachment type. You'll get the step rise, number of risers, total run, stringer length, stair angle, and a code compliance check.

inches

Total vertical distance from bottom to top of stairs

inches

Horizontal depth of each step

Calculation Method *

Only used in manual mode

inches

Thickness of the step boards

Unit System *

Results

Step Rise (Height)

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Number of Risers

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Total Run

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Stringer Length

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Stair Angle

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Code Compliance

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Results Table

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Frequently Asked Questions

What is the ideal step rise height for stairs?

The ideal step rise height is between 6.5 and 8 inches. Building codes typically require risers to be no more than 7.75 inches high, with a maximum variation of 3/8 inch between the tallest and shortest riser in a flight of stairs.

How do I calculate the number of steps needed?

Divide the total height by your desired step rise height. For example, if you have 84 inches of total height and want 7-inch risers, you need 12 steps (84 ÷ 7 = 12).

What is the minimum tread depth for deck stairs?

Most building codes require a minimum tread depth of 10 inches for exterior stairs. However, 11-12 inches is more comfortable for most people and provides better safety.

How do I calculate stringer length?

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

What's the difference between risers and treads?

Risers are the vertical parts of stairs (step height), while treads are the horizontal parts where you step. A flight of stairs typically has one more riser than treads.

Do my stairs need to meet building codes?

Yes, most jurisdictions have specific building codes for stairs including maximum rise height, minimum tread depth, and handrail requirements. Always check your local codes before building.

What angle should my stairs be?

The ideal stair angle is between 30-40 degrees. Angles steeper than 40 degrees become difficult to climb, while angles less than 30 degrees take up excessive space.

How thick should stair treads be?

For deck stairs, 2-inch thick lumber (actual 1.5 inches) is standard and meets most building codes. Thinner materials may not provide adequate support and durability.