How To Calculate Individual Riser Heights For Small Stairways
The first thing to point out is that we are trying to figure out the individual riser height, which is the height of each step going up the stairway. Each one of them should be the same size. The building codes usually allow a variance of up to 3/8 of an inch maximum.
Next, we need to take the overall height of the area that we are trying to calculate the individual risers for. This is usually not difficult. You will have an area where the stairs are going to be starting, maybe a flat landing, maybe a concrete pad for a deck, or any other situation where you have a lower level and an upper level and an area that you can measure. So that you can divide the amount of risers into this number to get the individual riser height.
This video is not going to provide you with information on how to cut stair stringers or to provide you with information on laying out the stair stringers, just the riser height so that you can lay out the stair stringers.
Now that you can see what the riser height is for this particular situation, let's go ahead and see how the author would figure it out if he didn't know how many risers he was going to have or how many steps he was going to need.
First, we will break out our trusty calculator and then take the overall rise or the distance between the lower level and the upper level and enter it into the calculator. The author breaks this down to inches and three foot one and a half inches is going to break down to 37 and a half inches. Then he puts that into the calculator 37.5 and divides it by the number seven, which equals 5.35.
Keep in mind that this is not our individual riser height. Remember for this example it is seven and a half inches, so we know this isn't it. But what the author is going to do is round this number off. To round the number off, you simply go to a higher or lower number. So if this was 5.7, he would round this off to a six. Anything less than 5.5 is going to get rounded down, anything that is 5.5 or higher is going to get rounded up. So if you have 5.5, feel free to use 5 or 6 for your number.
And of course, this number is simply going to be the number that we are going to divide into the overall total rise in hopes of getting our individual riser height. So let's go ahead and clear this 37.5 divided by 5, not 7, brings us to seven and a half inches.
And of course, for those of you who understand what we're doing here, feel free to stop watching, but the author is going to provide a couple of more examples. So let's go ahead and raise the height of this to three foot five and a half inches, which converts to 41.5 inches. Let's go ahead and put in 41.5 and we're going to divide it by seven, our magic number. Now we have 5.9, so he's going to go ahead and divide this by six.
Now this should make sense to you. He raised the height of this by four inches and now he's going to be adding another riser instead of dividing the number there by five, he's going to divide it by six. So let's go ahead and clear this 41.5 overall height and divide it by six, and that brings us to six point nine one six. And this right here is about a sixteenth of an inch, just a little over a sixteenth of an inch less than seven inches.
So again, hopefully not that difficult. And as you can see here, we have six units at six and fifteen sixteenths of an inch or six individual risers. Now here's what would happen if he divided it by five. He would have got a riser of eight and five sixteenths inches, just a little bit over eight and a quarter inches. And if your building codes don't allow more than an eight inch individual riser height, then this isn't going to work. So you're not going to get into any trouble by dividing different numbers into the original number here, just start with seven and then work your way up in either direction.
So if you do use the number seven and you get a number like a four or a five, you can use three, four, five, or six. You don't have to be set on one number. Divide a couple of different numbers into the total overall riser height to see if you can come up with the ideal riser height for your job. So again, seven is a good number to start with and then work your way in either direction.
Now for the last part of the video, the author is just simply going to take this number here and divide it by seven. So we divided it by six and came up with a riser height of almost seven inches, and now we divided by seven and come up with a riser height of almost six inches. So this is the perfect example of what he's talking about, taking and dividing a few different numbers into the overall riser height to get a riser height that you like and of course that would be accepted by your local building authorities or building department.
So hopefully this makes sense. You can now figure out the individual rise or height that is not that difficult. You're simply just dividing one number into another number to get the individual riser height, and of course you can use that measurement then to lay out your stair stringers or build your stairs if you're going to build them out of other materials.
Bonus Tips:
The author recommends getting a book on stair building, especially one of the double book packages that include different scenarios for the bottom of the stair stringer and the top. This is for wood framed stairways with something like a 2 by 12 or 2 by 14 for a stair stringer.
The author also recommends checking with your local building department for more information on building codes.
