For example, if you are building stairs to go up to a deck, and you measure 3 feet (0. 91 m) from the ground to the top of the deck, then this is the total rise. If you want the stairs to stop 3 inches (7. 6 cm) from the top of the deck, however, count the total rise as 2. 75 feet (0. 84 m).

For example, if your total rise is 95 inches (240 cm), divide it by 7 inches (18 cm) to get 13. 53. Round down to get the number of steps: 13.

To continue with the same example, divide 95 inches (240 cm) by 13 steps to get 7. 3125 inches (18. 574 cm). On your stringer, each step will rise 7. 3125 inches (18. 574 cm).

As a rule of thumb, the width of the treads and risers added together should equal between 16–18 inches (41–46 cm). So, if your riser is 7 inches (18 cm) tall, your tread should be anywhere from 9–11 inches (23–28 cm) long.

For example, the total run in our hypothetical example is 130 inches (330 cm): 13 total steps x 10 inches (25 cm) (tread width) each = 130 inches (330 cm) total run.

If your staircase will have landings, consider each section of stairs as its own mini staircase. [6] X Expert Source Agustin RenojHome Improvement Specialist Expert Interview. 13 January 2021. Always work your way up when building with a staircase landing. Start by building the first, lower half of the staircase with the landing. Once you’re done with that, work your way up to the second floor by building the upper portion of the staircase. [7] X Expert Source Agustin RenojHome Improvement Specialist Expert Interview. 13 January 2021.

Multiply the horizontal length (run) by itself, multiply the height by itself, and add the two results together. Then, find the square root of this sum. Keeping with the previous example, sqr(130 x 130) + (95 x 95) = 161 inches (409 cm)

For example, if your stairs will mount beneath an overhang of a deck, making sure that the top step isn’t level with the top of the deck. Instead, make the total rise slightly shorter and attach support posts to the top of the stringers.

For safety reasons, the stringers should be spaced approximately 16 inches (40. 6 cm) apart. Wider staircases are generally preferable to narrower ones because they are much easier and more comfortable to navigate.

Look for stair gauges at a hardware store. These are small knobs you can attach to your carpenter’s square at the right measurements to make marking and cutting a breeze.

Place the carpenter’s square over one corner of the lumber. Lay the side marking the height along the end of the lumber and the side marking the step depth along the length of the lumber. Draw a line between the step-height and step-depth marks. This line marks the horizontal top of your stringer. Mark the line so that its length is equivalent to the depth of one stair. Use the square to draw a perpendicular line from the end of the board to the spot you just marked. Cut along these lines.

Set the bottoms of the stringers on a firm footing like concrete, wood flooring, or even a block of treated lumber on top of gravel (for outside stairs). [18] X Research source

Cut 1 in × 6 in (2. 5 cm × 15. 2 cm) boards to the width of your stairs. Secure each stringer with 2. 5 in (6. 4 cm) screws. Ensure that the riser height is exactly the same for each step.

For instance, you could cut 1 in × 10 in (2. 5 cm × 25. 4 cm) lumber to the width of the stairs, and use this for your treads. For a special touch, use two boards and leave a 1⁄8–1⁄4 inch (0. 32–0. 64 cm) between them. For instance, you could cut 1 in × 5 in (2. 5 cm × 12. 7 cm) boards to the width of the stairs, and install two on each step, with a gap between them. To make extra-strong steps place 2 in × 4 in (5. 1 cm × 10. 2 cm) boards on both sides of the center stringer under the treads.

Almost any varnish, stain, or paint will work just fine for stairs. You can also use non-slip paint or put non-slip adhesive pads on the stairs.