Learn How to Measure Stair Stringers Correctly

Understanding Stair Stringer Basics

A stair stringer is the sloped structural board that supports the steps of a staircase. Think of it as the backbone of the stairs—it holds the weight of every person walking up or down. Most staircases use either one central stringer or two side stringers, depending on the width and design. The stringer contains cutouts or notches where the treads (the part you step on) and risers (the vertical boards between steps) attach.

Stringers come in different styles. Cut stringers have notches carved into them to hold the treads. Housed stringers have grooves routed into them where the treads slide in. Some staircases use cleated stringers, which have small supports called cleats underneath to hold the treads from below. Understanding which type you're working with matters because each one requires different measurement techniques.

Building codes in most areas require stringers to meet specific safety standards. These standards address how much weight they can hold, the angle of the stairs, and the spacing of the steps. The rise (height of each step) and run (depth of each step) must be consistent throughout the staircase. Most residential building codes require a maximum rise of 7.75 inches and a minimum run of 10 inches, though these numbers can vary by location.

The angle of your stairs affects how you'll measure the stringer. Stairs that are too steep (more than 50 degrees) feel unsafe, while stairs that are too shallow (less than 30 degrees) take up too much horizontal space. The ideal stair angle falls between 30 and 38 degrees for residential use.

Practical takeaway: Before measuring, identify what type of stringer you have and check your local building codes. This information shapes how you'll approach your measurements and ensures your work will meet safety standards.

Measuring Total Rise and Run

Total rise is the vertical distance from the bottom floor to the top floor. This is your first critical measurement. To measure it accurately, find the highest point of the finished floor at the bottom and the highest point of the finished floor at the top. Use a long level or a laser level to establish a straight horizontal line. The vertical distance between these two points is your total rise.

Many people make mistakes by measuring from the rough flooring instead of the finished flooring height. This causes problems because finished floors can vary in thickness. For example, if you're adding tile or carpet, the finished height will be different from the subfloor height. Always measure from where people will actually be walking.

Total run is the horizontal distance your staircase will cover from bottom to top. Imagine a bird's eye view looking down at your stairs—the run is how far forward the entire staircase extends. Measure this distance horizontally from the point directly below where the top of the staircase begins to where the staircase meets the lower floor.

If you have a total rise of 120 inches (10 feet), you'll need to divide this into individual steps. Building codes typically limit each step's rise to 7.75 inches. So 120 inches divided by 7.75 inches equals approximately 15.5 steps. Since you can't have half steps, you'd need 15 or 16 steps. With 16 steps, each rise would be 120 ÷ 16 = 7.5 inches. With 15 steps, each rise would be 120 ÷ 15 = 8 inches—which exceeds code limits. So in this case, 16 steps with 7.5-inch rises would work.

To find the total run, multiply the number of steps by the run depth of each step. If you have 16 steps and each step has a 10-inch run, your total run is 160 inches (about 13.3 feet). This is how much horizontal floor space your staircase needs.

Practical takeaway: Measure from finished floor to finished floor for accuracy. Calculate how many steps you need by dividing total rise by the maximum allowed rise per step (usually 7.75 inches). Then multiply the number of steps by your intended run depth to find total horizontal distance needed.

Measuring Individual Step Heights and Depths

Once you know your total rise and how many steps you need, you can calculate individual step measurements. Divide your total rise by the number of steps to get the rise per step. This number must be consistent across every single step in the staircase. Building codes typically allow a variation of only 3/8 inch between the tallest and shortest step.

For example, if your total rise is 120 inches and you're building 15 steps, each step's rise would be 120 ÷ 15 = 8 inches. Every step must be exactly 8 inches tall, or very close to it. Variations in step height cause people to stumble because our bodies expect consistency.

Individual step depth (the run) must also remain consistent. Most building codes require a minimum run of 10 inches, but many residential stairs use 11 or 12 inches for comfort. The run is measured from the edge of one tread to the edge of the next tread. Some people confuse this with the depth of the tread itself—remember that the run doesn't include the nosing (the part that overhangs the riser).

When measuring your stringer, you'll mark where each step's rise and run intersect. These intersection points create the notches in cut stringers. Use a framing square (also called a carpenter's square) to mark these points accurately. A framing square has two perpendicular arms—one is typically 24 inches and the other is 16 inches. You'll set the square to your rise and run measurements and slide it down the stringer, marking each step location.

On a 2x12 board (which is commonly used for stringers), you can typically fit about 12 to 14 steps before running out of board length. If you need more steps, you'll need a longer board or multiple stringers positioned differently.

Practical takeaway: Calculate rise per step by dividing total rise by the number of steps. Use a framing square set to your rise and run measurements to mark each step location on your stringer. Verify that every step rise differs by no more than 3/8 inch and that every run is consistent.

Using Tools and Technology for Accurate Measurements

Traditional tools like tape measures, levels, and framing squares remain the standard for stringer measurement. A 25-foot tape measure works well for most residential staircases. A 4-foot or 6-foot level helps you establish accurate horizontal and vertical reference lines. A framing square allows you to mark precise angles and step locations.

Digital laser levels have become increasingly popular for measuring vertical distances. These tools project a laser line that you can see across a long distance, making it easier to find the exact height difference between floors. A laser level can be especially helpful if your floor-to-floor height is greater than a standard tape measure can reach, or if there are obstacles in the way.

Stair calculator tools are available online and on smartphones. These calculators help you determine how many steps you need and what each step's rise and run should be based on your total rise measurement. You input your total rise, and the calculator suggests the number of steps and the height per step. While these tools can provide guidance, always verify calculations by hand because every staircase situation is unique.

A carpenter's pencil is better than a regular pencil for marking stringers because the flat edge helps you mark a consistent line. A chalk line can help you mark long straight lines across your stringer if you're working with a very wide board or multiple stringers.

String and a straightedge offer a low-tech way to verify that your stringer edge is truly straight before you begin marking steps. Stretch the string along the length of the board—if it touches at multiple points, the board is straight. If there are gaps, the board is warped and may not be suitable for stringers.

When using a laser level, make sure the area is well-lit so you can see the laser line clearly. Outdoors or in bright rooms, a laser level may be harder to see than in dim areas. Laser levels also need to be mounted securely on a tripod or wall to maintain accuracy.