How to calculate staircase dimensions

Written by r.l. cultrona
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How to calculate staircase dimensions
Staircase (Torsakarin/iStock/Getty Images)

Building a staircase may seem easy, but many a builder begining construction has found it wasn't as simple as it looked. This is because staircase construction requires extra math for the correct dimensions and correct number of stairs. Luckily the math involved in these calculations is equivalent to high school algebra and can be done quickly with a calculator, ruler, pen and paper.

Skill level:
Moderately Easy

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Things you need

  • Tape measure
  • Pencil
  • Paper
  • Calculator

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  1. 1

    Measure the total riser height. This is the height from the lower floor to the top of the higher floor. Write this number down.

  2. 2

    Divide the total riser height by the maximum height for each riser of your staircase. The International Building Code specifies that the maximum riser height is 190 mm (7 3/4 inches), but can be lower.

  3. 3

    Take the quotient (or result of the two numbers you just divided) and round up to the nearest whole number. Even if the quotient is 1/100 of a number, round up (for example, 7.01 will be rounded up to 8). This is the total amount of risers you will have. Write this number down.

  4. 4

    Divide the total riser height by the total number of risers to determine the actual height of each riser. You now know how many steps you will need and how high they will be.

  5. 5

    Multiply the total number of risers by 255 mm (10 inches). This is the total run of the stairs and gives you an idea about how far they will come out of the wall. Write this number down.

  6. 6

    Measure the distance from one side of the proposed staircase to determine its width. You should now be able to do all cutting as you have the total number of stairs, rise of each stair, distance from the back wall and distance from side to side.

Tips and warnings

  • If it makes the math easier, you can go as high as a 200 mm (8 inch) maximum riser. Typically, staircases have between a 175 and 200 mm (7 and 8 inch) rise. If you do use a 200 mm (8 inch) riser, however, you may not be in code, which could cause havoc if and when you decide to sell the house.

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