If you’ve ever stood at the top of a staircase and felt your foot land a half-inch off where you expected, you’ve felt what happens when rise and run aren’t calculated correctly. It’s the single most common mistake in stair building \u2014 and almost always avoidable with a little math before the first cut.<\/p>\n\n\n\n
This guide walks through exactly how to calculate stair rise and run, the code limits that constrain your options, and how those two numbers flow into everything else: step count, stringer length, and whether your staircase will pass inspection.<\/p>\n\n\n\n
Total rise<\/strong> is the total vertical distance your staircase needs to climb \u2014 floor to floor, or floor to landing. Total run<\/strong> is the total horizontal distance the staircase covers.<\/p>\n\n\n\n Those totals get divided into individual steps:<\/p>\n\n\n\n Get the total rise wrong and every riser in the flight is off by a fraction \u2014 which is exactly the kind of error your foot notices even when your eye doesn’t.<\/p>\n\n\n\n Measure the exact vertical distance from the finished floor at the bottom to the finished floor at the top, including the thickness of any subfloor or finish flooring that will be added later. This is the number the rest of the calculation depends on, so it’s worth double-checking with a laser level rather than a tape measure alone.<\/p>\n\n\n\n Divide your total rise by a target riser height \u2014 most residential codes cap this at 7\u00be” \u2014 and round up to the nearest whole number. That whole number is how many risers your staircase needs.<\/p>\n\n\n\n Once you have a whole number of risers, divide the total rise by that number again to get your actual<\/em> riser height. This is the number that keeps every step in the flight identical, which matters more to code inspectors \u2014 and to anyone walking the stairs \u2014 than hitting a “nice” round number.<\/p>\n\n\n\n Example:<\/strong> A total rise of 108″ \u00f7 7.5″ target = 14.4, rounds up to 15 risers. 108″ \u00f7 15 = 7.2″ actual riser height \u2014 under the 7\u00be” code max, and identical on every step.<\/p>\n\n\n\n Rather than run this by hand, the Stair Rise and Run Calculator<\/a> does steps 1 and 2 in one pass \u2014 enter your total rise and it returns riser count, exact riser height, and tread depth together. If you just need the riser count in isolation, the Number of Steps Calculator<\/a> handles that alone.<\/p>\n\n\n\n Tread depth is where the 7-11 rule comes in \u2014 a rule of thumb (not a code minimum on its own, but a useful starting point) stating that riser height plus tread depth should land close to 17\u201318 inches. A 7″ riser generally pairs with an 11″ tread; a steeper 7\u00be” riser pairs with a shallower ~10″ tread. Most residential code sets 10″ as the tread minimum regardless.<\/p>\n\n\n\n The Tread Depth Calculator<\/a> applies this ratio automatically against your riser height, and the Riser Height Calculator<\/a> works the same relationship from the other direction if you’re starting with a fixed tread depth instead.<\/p>\n\n\n\n Once riser height and tread depth are set, your stair angle is fixed \u2014 it’s not a separate decision. Most comfortable residential stairs land between 30\u00b0 and 35\u00b0 from horizontal; anything steeper starts to feel more like a ladder than a staircase, and anything shallower eats up a lot of floor space for the same total rise.<\/p>\n\n\n\n Run your numbers through the Stair Angle \/ Pitch Calculator<\/a> to see where you land, and if you need to compare that angle against a slope percentage for a permit drawing, the Rise\/Run Ratio to Degrees Converter<\/a> handles the conversion.<\/p>\n\n\n\n With riser height, tread depth, and total rise locked in, you can calculate stringer length \u2014 the diagonal board that carries the treads. This is also the point where most people discover their staircase needs a landing partway up, since a single stringer can only span so far before it needs intermediate support.<\/p>\n\n\n\n The Stair Stringer Calculator<\/a> takes your total rise and run and returns stringer length, cut angles, and how many stringers your stair width needs. If you’ve settled on standard 2×12 lumber for the stringers specifically, the 2×12 Stringer Board Calculator<\/a> factors in the material’s actual usable depth after the cuts.<\/p>\n\n\n\n Code requirements vary by jurisdiction and by whether the stair is residential or commercial, but these are the figures that come up most often under the IRC and IBC:<\/p>\n\n\n\n\n
Step 1: Measure your total rise<\/h2>\n\n\n\n
Step 2: Find your number of risers<\/h2>\n\n\n\n
Step 3: Set your tread depth<\/h2>\n\n\n\n
Step 4: Check your stair angle<\/h2>\n\n\n\n
Step 5: Size the stringers<\/h2>\n\n\n\n
Common code limits to check before you build<\/h2>\n\n\n\n