Stair Calculator

Measure the "Total Rise"—the vertical height from the lower finished floor to the upper finished floor. Divide this number by a desired riser height (around 7 inches is comfortable). Since you can't have a partial step, round the result up to the nearest whole number. This will be your total number of risers.

Our calculator automates this process to ensure code compliance and optimal comfort.

Rise is the vertical height of each step (from the top of one tread to the top of the next). Run (or "tread depth") is the horizontal depth of each step where you place your foot.

These two dimensions determine the steepness and comfort of the staircase. Together, they affect the stair angle and walking comfort.

This depends on the "mount type." In a "Standard Mount," the top floor acts as the final landing, so there is one less tread than there are risers. In a "Flush Mount," the top tread is one step down from the upper floor, meaning the number of treads equals the number of risers.

The floor itself is a landing, not a riser. Our calculator automatically handles this distinction based on your mount type selection.

This is a common DIY mistake. The bottom riser cut on the stringer must be made shorter than the others by the thickness of the tread material. When the tread is added, this brings the first step up to the same height as all the others.

Our calculator's "Height of First Step Cut" output provides this exact measurement to prevent this error and ensure all steps are uniform.

Individual run mode: Use when you know the depth you want for each step. The calculator will then determine how much total horizontal space the stairs will occupy.

Total run mode: Use when you have a specific horizontal space constraint. The calculator will determine the individual step depth that fits within that space.

Choose based on whether you're starting with step comfort (individual run) or space constraints (total run).

This calculator handles conversions automatically:

• Imperial to Metric: 1 inch = 2.54 cm, 1 foot = 0.3048 meters
• Metric to Imperial: 1 cm = 0.3937 inches, 1 meter = 39.37 inches

You can input measurements in either system and the calculator will display results in your preferred format. All internal calculations are done in inches for precision.

For planning purposes, measurements to the nearest 1/4 inch (0.25") are usually sufficient. However, for actual construction:

• Total rise: Measure carefully as this affects all other calculations
• Step dimensions: Precision to 1/16 inch (0.0625") is recommended
• Stringer length: Cut slightly long and trim to fit

Remember that small errors in rise or run can compound over multiple steps, so accuracy is important.

According to the International Residential Code (IRC), the key dimensions are:

• Minimum width: 36 inches
• Maximum riser height: 7 ¾ inches
• Minimum tread depth: 10 inches
• Minimum headroom: 6 feet 8 inches

Always check with your local building department, as they may have specific amendments to these requirements.

Building codes typically recommend:

• Rise per step: 7-7.75 inches maximum
• Run per step: 10-11 inches minimum
• Blondel formula: 2×rise + run should equal 24-25 inches
• Headroom: At least 6 feet 8 inches (80 inches)

The IRC specifies that a landing is required for any flight of stairs with a vertical rise greater than 12 feet 7 inches. A landing provides a necessary resting point on long staircases and helps prevent falls.

Landings are also required at the top and bottom of every staircase, regardless of height.

Yes, in most cases. The IRC requires a handrail on at least one side of any staircase that has four or more risers. The handrail must be:

• Continuous along the entire length
• Installed at a height between 34 and 38 inches above the stair nosings
• Graspable with a circular cross-section of 1.25 to 2 inches

Handrails provide stability and are especially important for children, elderly, and those with mobility issues.

Yes, when built correctly. The primary code requirement for floating stairs (which have open risers) is that the space between treads must be small enough that a 4-inch diameter sphere cannot pass through.

This rule is in place to prevent small children from falling through. Additionally, floating stairs must still meet all other code requirements for rise, run, and structural integrity.

The Blondel formula (2×rise + run = 24-25 inches) is a centuries-old rule that ensures comfortable stair climbing. It was developed by French architect François Blondel in the 17th century.

This formula creates stairs that feel natural to walk on - not too steep (which would be tiring) and not too shallow (which would feel awkward). Most building codes are based on this principle.

Headroom clearance is the vertical space between a tread and the ceiling above. To calculate it:

1. Measure the distance from the stair start to the floor opening edge
2. Find which step is directly under that point
3. Calculate the height of that step from the bottom
4. Subtract that height from the ceiling height at that point

The result should be at least 6 feet 8 inches (80 inches) for comfortable passage.

Warnings indicate that your stair design may not meet standard building codes or comfort guidelines:

• High rise: Consider adding more steps to reduce the rise per step
• Low run: Increase the total run or reduce the number of steps
• Steep angle: Make the stairs less steep by increasing run or reducing rise
• Blondel formula: Adjust rise and run to get closer to 24-25 inches

While you can still build stairs outside these guidelines, they may be less comfortable or fail building inspections.

For outdoor stairs, resistance to rot and insects is crucial. Common choices include:

• Pressure-Treated (PT) Lumber: The most affordable and structurally strong option, chemically treated to resist moisture and insects.
• Cedar: Naturally resistant to rot and insects, lightweight, and has a beautiful appearance.
• Redwood: Similar to cedar in its natural resistance but is denser, more durable, and generally more expensive.

Always use appropriate fasteners and finishes for outdoor applications.

The industry standard is 2x12 lumber. Using smaller lumber, like 2x10s, often does not leave enough solid wood behind after the notches are cut, which can compromise the structural integrity of the staircase.

2x12s provide adequate strength and allow for proper tread and riser attachment while maintaining structural safety.

Proper attachment is critical for safety. Toe-nailing is not permitted by code. The recommended methods are:

• Metal Hangers: Use galvanized steel stringer connectors (like the Simpson LSCZ) specifically designed for this purpose.
• Structural Fasteners: Attach the stringers directly to a solid header or a doubled-up rim joist using ½-inch diameter lag bolts or structural screws.

Always follow manufacturer specifications and local building codes for proper installation.

For interior wood treads, polyurethane is the most durable choice due to its high resistance to foot traffic. It is available in:

• Oil-based: More durable, amber tone, longer drying time
• Water-based: Dries faster, clear finish, easier cleanup

Applying at least three thin coats is recommended for a long-lasting finish. For outdoor stairs, use exterior-grade finishes designed for UV and moisture resistance.

A stringer is the diagonal supporting beam that runs along the side of the stairs. It's what the treads and risers are attached to.

Stringer length is calculated using the Pythagorean theorem: √(vertical² + horizontal²). The vertical dimension depends on your mount type and whether you have tread boards.

This measurement is crucial for cutting the stringer boards to the correct length during construction.

Standard mount: The stringer is mounted below the top landing. The top step has a separate tread board, and the stringer doesn't reach the full height of the upper floor.

Flush mount: The stringer is cut to be flush with the top floor level. The upper floor itself acts as the last tread, and you typically have one more riser than in standard mount.

Flush mount is often used when you want the stairs to blend seamlessly with the floor above.

Tread boards are separate pieces of material (usually wood) that sit on top of the structural steps to provide the walking surface.

You need tread boards when:

• Building traditional wood stairs
• Wanting a finished walking surface
• Using open risers (no vertical boards between steps)

If you're building solid concrete or metal stairs, you might not need separate tread boards.