How to Calculate Where the Landing Is on Deck Stairs

Building codes generally require a ground landing for exterior stairs and intermediate landings where steps exceed a certain number or height. Intermediate landings make the climb more comfortable, even where not required by code, and bottom landings prevent hazardous erosion of the ground at the base of the stairs. Finding the location of the landing is straightforward once the rise and run of the stairway are known, though some adjustments may be necessary before the work begins. Calculations for stairs aren't difficult, but stair building requires accuracy, and it's best to check your calculations several times.

Measuring tape
Calculator
Grade stake
Waterproof marker

Instructions

- 1
  Find the total rise -- the vertical distance from the surface where the stairs begin to the finish surface of the upper deck. Divide the result by the desired riser height -- usually 7 inches -- to find the number of risers. Round the result up or down to the nearest whole number.
- 2
  Divide the total rise by the whole number to find the exact height of each riser. Choose the tread depth -- a comfortable ratio for exterior steps is 2 x riser height + tread = 25 inches.
- 3
  Find the number of treads by subtracting 1 from the number of risers. Multiply the number of risers by the tread depth to find the total run -- the horizontal distance between the deck surface and the bottom of the first riser.
- 4
  Add the width of the intermediate landing to the total run -- a minimum of 3 feet or as required by code. Plan the location of the landing after a certain number of risers -- seven or eight is recommended. Multiply the tread depth by those seven or eight risers to find the location of the landing at the top of the seventh or eighth riser. Start the next flight of stairs at the end of the landing.
- 5
  Locate the ground landing at the base of the first riser and extend it at least 3 feet or as required by code. Slope the landing away from the stairs to drop 1/4-inch per foot.
- 6
  Mark the top of the bottom landing on a grade stake with a waterproof marker and check the calculations. Adjust the stair dimensions or shift the layout as necessary.

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