How to Properly Measure for Outdoor Steps


General Considerations
For amateurs and professionals alike, building an outdoor staircase can be intimidating. But like any building project, if properly measured and planned, it should be completed without too much difficulty.

It’s important to note beforehand that local building codes have regulations on the width and slope of a staircase, as well as how it’s braced and supported. Always check your local regulations before designing your stairway, being sure to follow local building codes.

The following are general instructions on how to measure for a straight-run stairway, and are intended only as guidelines.

Stair-Building Terms
TOTAL RUN: the total horizontal distance of the staircase. This includes everything from the edge of the top step to the edge of the stairs where they rest on the ground.

TOTAL RISE: the total vertical distance from the ground to a point level with the surface of the top step. It’s important to note that you can’t measure the rise just by measuring straight down from the top step. This is because the ground directly below may not be level with the landing.

RUN: the horizontal distance covered from the leading edge of one step to the leading edge of the next step.

RISE: the vertical distance from the surface of one step to the surface of the next step.

PASSAGE WIDTH: the width of the stairway.

The ratio of the total rise over total run will determine the slope of the stairway. An ideal riser height is 7″ with an 11″ run. You may have to vary the proportions to on your stairway to make sure the height for each step works out evenly between the landing and the top step.

The passage width can also have some variation. But that all depends on how much traffic you expect on the stairs. Normally 36″ is the minimum, but 48″ is better for a single person. You may wish to go out to 60″ to allow enough room for two people to pass each other comfortably.

Stair Components
STRINGERS: the sloped members that support a stairway. 2 x 1Os are generally used for stairs with four steps or fewer, but 2 x l 2s are much sturdier.

TREADS: the horizontal members that you walk on, otherwise known as the steps. When building an outdoor stairway, they are usually cut from the same material as the upper floor deck or porch.

RISERS: the vertical members at the back of each step. For these, l” surfaced boards (3/4″ net thickness) are the most commonly used materials.

THE RAILING ASSEMBLY: made up of several posts with vertical balusters between them, and a cap rail. A 4×4 is the most common post material, with a 2×4 handrail.

Designing Your Stairs
When you begin to design your stairway, first you must measure the total rise. Then divide that number seven, because 7″ the ideal step height, to find the total number of risers. More than likely you will have a fractional number, so round to the nearest whole number.

Then you will divide the total rise by your answer to get the exact height between each step. For example:

1) Total rise = 40-1/2″
2) 40-1/2″ divided by 7″ per step = 5.78 steps
3) Round 5.78 up to 6 steps, then 40-1/2″ divided by 6 = 6.75″ or 6-3/4″ per step

Use the following table to determine the width of your steps, depending on your step height:

Riser Height Run Width
6″ 14″
6-1/4″ 13-1/2″
6-1/2″ 13″
6-3/4″ 12-1/2″
7″ 12″
7-1/4″ 11-1/2″
7-1/2″ 11″

To find the amount of material you will need for each step, multiply the number of steps by the total passage width. To find the amount of needed tread material, subtract one from the number of steps and multiply that by the passage width. Remember if you’re using two boards to form a single step you will need to double your number.

To find the length of each step, you will need a calculator or phone app with the square root function. First find the total run. This is the number of steps multiplied by the width of each step.

Then use your calculator to get the square of the total run. The square root of this answer will give you the needed stringer length. This answer will be a fraction, but instead of rounding up to the nearest whole number you will be rounding up to the nearest length of standard lumber. Once you’ve rounded, multiply by the number needed stringers.

No that that you have all your measurements you should be ready to begin building your outdoor stairway. If you have any questions about building materials, your local hardware store or lumberyard can be a good source of information and advice on what to use. Though it may all seem overwhelming in the beginning, with proper preparation and planning your outdoor stairs should come together smoothly and efficiently.