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Stair Rise and Run Calculator

Mastering Stair Calculations

Have you ever dreamt of designing and building your own stunning staircase but hesitated due to complex calculations? Or maybe you’re building or redoing your staircase and can’t make heads or tails of the stair rise and run that you need? Even if you just want to have an informed conversation with your stair builder, a understanding your stair rise and run with a calculator will reap many benefits. 

This post with help you perform stair rise and run calculations and is your one-stop guide to conquering stair math. 

We’ll break down everything you need to know about calculating stair rise, run, angle, and even stringer length. 

Plus, we’ll delve into determining step height, tread depth, and the magic number – the number of steps required for your specific project.

By the end of this post, you’ll be wielding the power of stair calculations with confidence, ready to tackle your next home improvement project with expertise (and maybe a little pride!). 

So, grab your measuring tape and settle in – it’s time to take your DIY skills to the next level!

Stair Terminology

First let’s start with the basics. If you know your stairs, feel free to skip this part, if you need more details, check out our parts of a staircase glossary of terms.

For everyone else, learn these terms to fully understand your stairs:

  • Tread: The horizontal surface you step on when walking up the stairs.
  • Riser: The vertical part of a step between two treads.
  • Run: The total horizontal distance covered by the entire staircase.
  • Rise: The total vertical distance between the starting and ending points (floor to floor).
  • Stringer: A sloped structural support beam that supports the treads on one or both sides of a staircase.
  • Landing: A platform that creates a turn or separates flights of stairs.
  • Balustrade: The railing system along the open side(s) of a staircase, consisting of a handrail, balusters (spindles), and sometimes a baserail.
  • Handrail: The horizontal part you grasp for support while walking up or down the stairs.
  • Baluster (Spindle): The vertical posts that support the handrail and fill the space between it and the treads.
  • Nosing: The overhanging front edge of a tread.
  • Newel: A large post at the top or bottom of a staircase that supports the handrail and connects it to the floor or landing.

Stairs With Risers

As you now know, risers are the verticals between stair treads. 

Most stairs over 30 inches will need risers. The good news is, if you attach the riser before the tread, they won’t impact the stair calculation.

Here’s how to calculate stair risers:

  • Measure the total rise: This is the vertical distance between your starting and ending points (floor to floor).
  • Choose a comfortable riser height: Consider building codes (typically 6″ to 7.5″) and user comfort.
  • Calculate the number of steps: Divide the total rise by your chosen riser height (rounded up to the nearest whole number).
  • Verify the total run (horizontal distance): Building codes often specify a minimum run based on your riser height. Multiply the number of steps by your chosen tread depth (typically 10″ to 12″) to get the total run.
  • Adjust if necessary: If the total run doesn’t meet code requirements, try a different riser height and recalculate everything.

How To Calculate Stair Stringers

Stair stringers are the vertical timbers that make up the main structure of a stair. They will have notches cut for risers and treads.

Here’s how to calculate stair stringers:

  • Gather your measurements: You’ll need the total rise (vertical distance), total run (horizontal distance), and desired tread depth (horizontal walking surface).
  • Calculate the number of risers: Subtract the thickness of your tread material (usually 1″ to 1.25″) from the total rise. Divide this number by your chosen riser height (rounded down to the nearest whole number).
  • Lay out the stringer: Draw a right triangle on your stringer material. The base of the triangle equals the total run, and the height equals the total rise.
  • Mark the tread notches: Evenly space the desired number of risers (plus one for the top step) along the hypotenuse (diagonal line) of your triangle. Project horizontal lines from these marks to the base to define the width of each tread.
  • Mark the nosing (optional): If you plan for treads to overhang the stringer, add your desired nosing overhang distance to the front of each tread line.
  • Cut and notch your stringer: Use a saw to follow your markings, creating notches for the treads to rest on.

Common Stair Building Codes

If you’re building stairs from scratch and want them to comply with code, you’ll need to know the rules.

While every state and county may be different, the following are common stair building codes you need to know:

Minimum Width:

  • Residential stairs: 36 inches (may allow for some handrail projection)
  • Commercial stairs: Varies depending on occupancy (typically 36-48 inches)

Riser Height:

  • Maximum: 7 ¾ inches (some variations depending on code)
  • Minimum: Varies by code (often 4 inches)
  • Consistency: All risers in a single flight should be within ⅜ inch of each other.

Tread Depth:

  • Minimum: 10 inches with nosing, 11 inches without nosing
  • Maximum nosing projection: 1 ¼ inches

Headroom: 

  • Minimum of 6 feet, 8 inches clear vertical distance between the tread and the ceiling above.

Handrails: 

  • Required on at least one side of the stairs, with a maximum grip diameter and specific height from the tread.

Check the codes for your specific region before you begin building in case of any variation.

Stair Tread

Stair tread codes focus on providing a safe and comfortable walking surface. 

  • Minimum depth: 10 inches with a nosing overhang (the tread projecting past the riser), or 11 inches without.
  • Maximum nosing overhang: 1.25 inches.
  • Consistency: All treads in a flight must be within 3/8 inch of each other in depth.

These rules ensure a predictable step size for safe and easy climbing.

Stair Riser

Stair riser codes are all about creating a comfortable and secure ascent. 

  • Maximum height: Typically 7 ¾ inches, but can vary slightly depending on the specific code.
  • Minimum height: Usually around 4 inches, but again, consult your local code for specifics.
  • Consistency is key: All risers within a single staircase flight must be within ⅜ inch of each other in height.

Nosing

Stair nosing codes are designed to prevent slips and falls. 

  • If present, maximum overhang is typically 1 ¼ inches.
  • Provides a clear visual definition of the tread edge, especially helpful in low-light conditions.
  • May also improve slip resistance by adding a textured material to the overhang.

Headroom

Stair headroom codes prioritize safety and allow for comfortable movement.

  • Minimum clearance: A minimum of 6 feet, 8 inches (2032 mm) vertically from the leading edge of the tread (nosing or flat front) to the ceiling above.

This ensures ample headroom to avoid bumping your head while navigating the stairs.

Applies throughout the entire stairway, including landings.

Stair Width

Stair width codes are crucial for safe building egress and depend on occupancy:

  • Residential: Minimum 36 inches clear width between handrails. May allow for some handrail projection.
  • Commercial: Varies based on occupant load (typically 36-48 inches). Higher occupancy requires wider stairs for faster evacuation.
  • Accessibility: Wider widths (often 48 inches) are mandated for stairs serving as accessible exits, ensuring safe passage for everyone.

Handrails & Guards/Guardrails

Stair guardrail codes prioritize fall prevention, especially for stairs with a significant drop. 

Required on open sides of stairs exceeding 30 inches in height.

  • Minimum height: Typically 36 inches in residential settings, 42 inches in commercial settings.
  • Handrail must be graspable and continuous along the entire staircase run.
  • Maximum distance between handrail and wall: Around 3.5 inches for comfortable gripping.
  • Load-bearing capacity: Must withstand a 200-pound force applied in any direction.

Stringer

While there aren’t specific size requirements for stair stringers, building codes do address their overall strength and support.

  • Stringer sizing: Must be strong enough to support the anticipated weight load on the stairs (typically 300 pounds concentrated load or 100 psf).
  • Material and construction: Engineered wood, steel, or concrete are common options, and their sizing depends on span and load.
  • Support: Stringers need proper anchoring at the top (floor or landing) and bottom (floor or footing).
  • Span limitations: Generally, unsupported spans for closed stringers shouldn’t exceed 13 feet 3 inches, and cut stringers need additional support around 6 feet.

Height of First Step

There are no specific codes addressing the height of the first step itself. Stair riser codes apply to all risers within a single flight, ensuring consistent and predictable step patterns.

However, general building codes for headroom (minimum 6 feet, 8 inches) indirectly impact the first step.

  • Headroom is measured from the leading edge of the tread (including nosing if present) to the ceiling above.
  • Since all treads (including the first) must comply with headroom requirements, the first step riser height aligns with the overall riser design.

Number of Steps

Building codes don’t dictate the exact number of steps in a staircase. Instead, they focus on riser height and total rise (vertical distance).

  • Riser height: Codes specify a maximum and often a minimum height (e.g., 7 ¾ inches max, 4 inches min).
  • Total rise: Measured from floor to floor.
  • Number of steps: Divide the total rise by your chosen riser height (rounded up to the nearest whole number).

Stairs and Landings

Stair and landing codes promote safety and functionality during stairway use.

  • Landings: Required at the top and bottom of every stairway.
  • Landing size: Minimum width must match the stair width, and minimum depth is either the stair width or 48 inches, whichever is less. This allows for safe maneuvering at turns or exits.
  • Door swing: Doors opening onto landings can’t reduce the usable landing area below half its required width and shouldn’t project more than 7 inches when fully open.
  • Handrails: Landings with open sides over 30 inches deep need to continue the handrail system for uninterrupted support.

Calculating Your Stairs

So there you have it! Your complete guide to calculating stairs with common building code guidelines to help you on your way.

Interested in bespoke custom stair parts or any help with custom millwork for your own staircase? Contact Dutchess Millwork today for a fast, free quotation!