Rise and run are the two basic measurements that define every staircase. Rise is the vertical height of each step. Run is the horizontal depth of each step, measured from the front edge to the back. Together, they determine how steep or gradual a staircase feels, how safe it is to walk on, and whether it meets building code.
Rise vs. Run Explained
Think of each step as a small right angle. The rise is the vertical part (the riser board you see on the face of each step), and the run is the horizontal part (the flat surface your foot lands on, called the tread). Every staircase repeats this pattern from bottom to top.
These terms also apply to the staircase as a whole. The total rise is the full vertical distance from the finished floor at the bottom to the finished floor at the top. The total run is the full horizontal distance the staircase covers. When people refer to “unit rise” and “unit run,” they mean the dimensions of a single step.
What Building Codes Require
For residential construction, the International Residential Code sets clear limits. The maximum riser height is 7¾ inches (197 mm), and the minimum tread depth is 10 inches (254 mm). This is sometimes called the “7-11 rule,” though the actual code allows slightly more rise and slightly less run than those round numbers suggest.
Commercial buildings follow the International Building Code, which is stricter. Stairs in commercial spaces and multi-family buildings (outside individual units) have a maximum riser height of 7 inches and a minimum tread depth of 11 inches.
One critical rule applies to both: within a single flight of stairs, the tallest riser cannot differ from the shortest by more than ⅜ inch. Uneven steps are a leading cause of stairway falls because your body expects each step to feel the same. Even a half-inch variation can catch your foot off guard.
Why These Numbers Matter for Comfort
The relationship between rise and run isn’t arbitrary. In the 17th century, a French architect named François Blondel proposed a formula that’s still used today: twice the rise plus the run should equal a comfortable human stride, roughly 24 to 27 inches (600 to 700 mm). So if your rise is 7 inches, the formula suggests a run of about 10 to 13 inches.
Research on stair safety narrows these ranges further. Riser heights between about 6¼ and 7¼ inches produce the fewest missteps when going down, which is when most stair injuries happen. A tread depth of roughly 11 to 11½ inches works well for about 95% of the population, giving enough room for the ball of your foot to land securely. Steeper stairs with shorter treads force you to descend at an angle, which increases the risk of slipping.
How to Calculate Rise and Run
If you’re building or replacing a staircase, the process starts with one number: total rise. Measure the vertical distance from the finished floor at the bottom to the finished floor at the top. This is the number everything else depends on.
Divide the total rise by your target step height. Most builders aim for around 7 inches per step. For example, if your total rise is 108 inches (9 feet), dividing by 7 gives you about 15.4. Since you can’t have a partial step, you’d round to either 15 or 16 risers. With 15 risers, each step would be 7.2 inches tall. With 16, each step would be 6.75 inches. Both are within code, so you’d choose based on available space and comfort.
Next, determine the run. With a 10-inch tread depth and 15 risers, you’ll have 14 treads (there’s always one fewer tread than riser, because the top floor itself acts as the last step). Multiply 14 treads by 10 inches, and your total run is 140 inches, or about 11 feet 8 inches of horizontal floor space.
If you don’t have that much room, you can increase the riser height slightly (reducing the number of steps) or reduce the tread depth, staying within code limits. These tradeoffs are the core of stair design.
Tread Depth vs. Nosing
One detail that confuses many people: the tread depth used for code compliance is measured from the front edge of one step to the front edge of the next, not the full width of the board. Most treads have a nosing, a small overhang that extends past the riser below. The nosing makes the stair more comfortable by giving your foot extra landing area, but it doesn’t count toward the run measurement. So a board that’s 11½ inches wide with a 1¼-inch nosing has an effective run of about 10¼ inches.
Putting It Into Practice
When planning stairs, write down three things before you cut anything: the total rise (measured, not assumed from blueprints), the number of risers that gives you a step height under 7¾ inches, and the tread depth that keeps you at or above 10 inches. Then check the math both ways. Multiply your unit rise by the number of risers to confirm it equals the total rise. Multiply your tread depth by the number of treads to confirm the total run fits in your available space.
If any single riser ends up more than ⅜ inch different from the others, recalculate. Consistent steps are more important than hitting a specific height, because your legs learn the rhythm of a staircase after the first two or three steps and expect it to stay the same all the way up and down.