Calculating risers and treads is a necessary part of building a set of stairs right the first time, without having to tear them out and start over again. Do-it-yourselfers who have never built a set of stairs before will be taking on a challenging task. Not knowing what to measure and how to do the calculations needed to properly size the stairs to fill the available space is at the heart of most stair/step building failures.
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Things you need
- Tape measure
Measure to find the total height of the stairs/steps. Stand at what will be the top of the stairs. Extend an aluminium tape measure to the ground or next floor below. Write down that measurement.
Calculate the riser by dividing the measurement in Step 1 by 7. Seven inches is the standard height of each step. For example, if the total height determined in Step 1 is 56 inches, divide this figure by 7. Record the answer: 8. This is the number of risers you will need to cover the total height distance.
Calculate for unevenly numbered heights since more distance has to be covered by the stairs. (It is the same if less distance needs to be covered.) For instance, if the total height to be covered by the set of steps is 57 inches, divide 57 by 7 for a quotient of 8.14. Round down the answer to 8. Divide 8 into 57 to get a quotient of 7-1/8 inches. This is the correct riser height for the uneven height of 57 inches.
Determine the number of treads you'll need by calculating the total run of the stairs. Figuring the total horizontal distance will tell you how many treads will be needed. Use the horizontal distance to calculate the horizontal depth of each tread. The average run of each step is 10 inches. Multiply the number of steps (8) by 10. This is the total run/horizontal distance calculation: 80 inches.
Multiply the number of steps (8) by 2 to get the exact number of 2x6 treads which are 4 feet wide (or wider). (Typically, 2x6 boards laid side-by-side equal a little over 11 inches, almost 12 inches when you allow a ¼-inch gap between the tread boards. This will leave a 1-inch plus overhang for each step.) Two 2x6 boards per tread, times 8 steps equals 16. Cut 16 2x6 boards into 4-foot lengths. These will make up the treads.
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