Calculate The Stair Angle
Measure the rise/run of your stairs.
- The rise is the vertical distance that your stairs cover. You can measure 1 step from bottom to top (a) if your stairs are all a uniform height. If not, measure the entire rise from the ground to the top of the top step (A).
- The run is the horizontal distance that your stairs span. Again, you can measure 1 step tread from front to back (b) if your stairs are uniform. If not, measure from the bottom edge of the first step to the point on the ground under the edge of the top step (B).
2) Plug the rise/run into an angle calculator.
|Click the screenshot to go to the stair railing angle calculator|
- No need to be overly complicated here and work out the trigonometry ourselves. There are plenty of free tools online to calculate angles. Try this one, which can be accessed through the web, or downloaded as an app. Make sure to hit the angle button before entering the rise & run, then hit calculate.
Calculate The Stair Railing Length
1) Let Pythagoras Be Your Friend
- In the drawing above, the rise is the distance from the surface of your deck to the ground. The run is roughly the distance from the spot on the ground where your railing post will be anchored to the spot on the ground under where your top railing post will be anchored. That's a little different measurement then the rise & run in the angle calculation above. The reason is that the length of the railing depends on where you set your posts.
- Remember in high school when you slept through geometry on the premise that you would never use it? Well, think again. Calculating the length of your stair railing actually is actually based on a fundamental relationship in geometry called the Pythagorean Theorem, which basically states (in terms of railing) that the squared length of your stair railing is equal to the squared rise of your stairs + the squared run of your stairs, or A^2 + B^2 = C^2.
For example, suppose your rise & run (A & B in the drawing above, respectively) are 40" & 60".
Then: 40^2 + 60^2 = C^2
working through this problem gives us the following steps:
1) 1600 + 3600 = C^2
2) 5200 = C^2
3) C = the square root of 5200
4) C = 72.11 inches
So the length of stair railing that you need is 72.11 inches. Which brings us to another important point. Since most outdoor stair railings come in whole sizes like 3ft., 4ft., 5ft., etc. what do you do when your measurment is between 2 sizes? The answer is that you probably need to round up to the next size. In this case though, .11 inches isn't very much and we could probably move our posts closer together by that much and stick with the 72" or 6' railing.
Once you have all of your measurements in hand, you're ready to order your outdoor railing system. Check out the fantastic Westbury Aluminum Railing System. It comes in multiple styles, sizes, and colors and it's easy for do-it-yourself installers.