How to Design an Outdoor Stair

What You'll Need

Carefully designing an outdoor stair is a crucial step in building a stairway. Learning how to design an outdoor stair can be hard on your brain. But don’t be disheartened. With some easy-to-get tools and this guide, designing an outdoor stair is just another job you can do yourself.

Step 1 – Determine Total Run and Total Rise

The total rise is the total vertical distance from the ground to the raised surface where the stairs will stretch to. The total run is the total horizontal distance of the stairs. Total rise over the total run is the slope of the stairs. When you are determining the total rise and total run, you must make sure that the slope is around 30 degrees to 35 degrees.

Step 2 – Calculate the Number of Steps

Divide the total rise by 7. The calculated number is the number of steps needed in your outdoor stairs. You may have to round up or down in order to obtain a whole number. A quick tip: when you are measuring the total rise you cannot simply run a ruler straight down from the upper floor. The ground directly under the upper floor may not be level with the ground the stair starts from.

Step 3 – Calculate the Width

The width of the stairs depends on the riser height. Risers are the vertical boards fixed at the back of each steps. To calculate the riser height, divide the total rise with the number of steps. Then use the recommendations below to determine the width of the stairs. "Riser Height" and "Run Width" are in inches.

Riser Height

Run Width















Step 4 – Calculate Materials Needed for Risers and Treads

The number of risers needed for the stairs is equal to the number of steps. Multiply the number of risers by the width to figure the materials needed for the risers. Then determine the amount of tread, or step, material needed by multiply the passage width by the one less the number of risers.

Step 5– Calculate Materials Needed for Stringers

Stringers are the sloped boards that provide support the stair. The gap between stringers cannot be bigger than 24 inches if the treads are built with 5/4 inch, and no more than 36 inches apart if the treads are built with 2 inch lumber. Square root the sum of total run squared and total rise squared to determine the stringer length. Round up the stringer length to the nearest standard lumber length and multiply that number by the required number of stringers to calculate the materials needed for the stringers.

Step 6 – Compile into a Blueprint

Gather all the mathematical data and form it into a blueprint with pen and paper. Include the total rise, total run, stringer length, riser height, run width and passage width in the blueprint. Passage width can vary depending on how heavily the stairs is to be utilized. Thirty six inches is the minimum length. Forty eight inches is ideal for a single person use. Sixty inches passage width can support 2 people at once. If you prefer, you can add handrails to your design. However, it must fit the local regulations. The local code regulates the total height of the railing and sometimes the maximum width.