Proper Deck Baluster Spacing: A Practical Guide [With Calculator]

When I was building my first deck, one question I ran into was deck baluster spacing. I knew they couldn’t be too far apart, but I wanted them as far apart as possible to achieve a certain look. After some research, I found that there is a maximum gap size that is universal throughout North America.

Deck balusters must be no more than 4” apart. Balusters can be either vertical or horizontal – or diagonal if you’re feeling ambitious – but the gap between balusters cannot exceed 4 inches. You can anchor your balusters to the deck, or if you choose, a rail that can be no more than 4” from the deck surface.

In this article, we’ll dig a little deeper and go over building code requirements for baluster spacing on decks, deck stairs, deck landings, and how to calculate baluster spacing on your next deck project.

Deck baluster spacing


Are Balusters and Spindles the Same Thing?

Yes and no. Generally speaking, balusters and spindles perform the same function in a deck railing system. They are the vertical supports that connect the top railing to either a bottom railing or the deck surface.

For the most part, people tend to interchange the two terms. But there is a difference in terms of appearance.


A spindle is narrower than a baluster, is often turned on a lathe (cylindrical), and can have some decorative features on the top or bottom. Many prefabricated aluminum railings use aluminum spindles – they are simply narrow columns. These are ideal if you want a good line of sight through your railing system.


Balusters are not as narrow as spindles, are also usually turned on a lathe, and often have decorative features such as a unique profile on the top and bottom. Metal balusters may have an arc and are not cylindrical, but rather flat on either side. High end pre-fabricated aluminum railing systems use this style.


Don’t forget about ‘pickets’ and ‘uprights’. You may hear about those terms in place of ‘baluster’. Generally, a picket is simply a rectangular piece of wood with angled ends on each end. These are commonly found in bundles at home reno stores and also on cheaper prefabricated railings at those same stores. Most often, they are about 1.5” wide – 2” at the most.


Last but not least, don’t forget about the uprights. An upright is a general term to describe a baluster. It would usually refer to a picket, although this term simply isn’t used much anymore.

Deck Baluster Spacing Code

Let’s get the important info out of the way right now: the space between your deck balusters – stairs or deck – cannot be more than 4 inches.

When an inspector comes to check your deck, he’ll have a 4” spherical ball. That’s what he uses to check your baluster spacing. If the ball can squeeze through fairly easily, then you’re going to have to redo those balusters and make them closer.

Instead of risking having a uptight inspector ruin your day, make your balusters 3.5” or less. That leaves you some room for error without risking having that ball sail through your balusters.

Deck spindle spacing


Deck Stair Baluster Code

See above. The same 4-inch requirement holds true when putting a railing on your deck stairs. Below we’ll go over more in-depth about putting balusters on your deck stairs, but for now, you just need to know that deck railings and stair railings have the same requirements.

Other Important Baluster Spacing Codes

Note that your railing cannot have more than a 4” space between the deck surface and the bottom of your bottom rail. This does not apply to decks whose balusters attach to the deck itself and not a bottom rail.

Again, to avoid problems, space your bottom rail 3.5” from the deck surface to satisfy building code.

Also, remember that your railing must be 3’ from the surface of the deck – minimum. So if you are making your own balusters, just know that you aren’t cutting pieces that are less than 3’.

You’ll need a railing and balusters if your deck is more than 2’ off the ground. Your stairs will also need a railing if there are more than two stairs.

Another important code pertaining to deck balusters is that they must be able to withstand a point load of 125 pounds. The top rails must withstand a load of 200 pounds. Engineers prefer to multiply each by 2.5 to ensure safety, so ideally your balusters should be able to withstand a 300 lb. load and your top rail 500 lbs.

Be sure to conform to building codes. A building inspector can potentially hit you with some fines if he comes out and finds you have spaced your balusters too far – he’ll also make you redo the whole railing and possibly make you pay another fee.

Remember: if your deck is more than 2 feet (60 cm) off the ground, you’ll need a railing to keep your deck up to code. Your railing can’t be less than 3 feet (90 cm) from the surface of the deck. And no matter where you are in North America, the rule of 4” (or 10cm in Canada) remains consistent for baluster spacing.

Calculating Deck Baluster Spacing

One of the more frustrating aspects of building a deck railing is figuring out how many balusters you’ll need for your entire railing. In this section, we’ll give you the tools you need to accurately assess exactly how many balusters you’ll need.

There are two ways to calculate the total amount of balusters you’ll need.

Calculate Deck Baluster Spacing Yourself

It’s easy – here’s how:

  1. Find your total railing length in inches.
  2. Subtract the width of each post in your railing system from the total length.
  3. Divide that number by the width of your baluster plus the width of your gap between balusters.
  4. The answer is the number of balusters you’ll need.

Here’s a real-life example to better show you how to calculate deck baluster spacing yourself.

Let’s say you are building a 12’ x 8’ deck, with railings on only two sides. That means you’ll need (12’+8’ =) 20’ of the railing. Since we need to know the inches, we multiply 20’ x 12” = 240”.

Now, you are using 4×4 posts as your railing posts. You have 5 posts. The actual width of a 4×4 is 3.5”, so you’ll need to multiply 3.5” x 5 = 17.5”.

Subtract 17.5” from 240” = 222.5”

Now you need to know the width of your baluster and the gap you want between your balusters. If your baluster is 1.5” and your gap is 3.5”, then you add them together, which equals 5”.

Last, you divide 222.5” by 5” = 44.5. You’ll need 45 spindles to adequately cover a railing for two sides of your new 12’x8’ deck.

Deck Baluster Spacing Calculator

Here’s the deck baluster spacing calculator that will tell you how many balusters you’ll need per the length of your railing. While the calculation isn’t that complicated, I recommend using this tool to at least check your math after you’ve calculated it yourself.

To use the tool, you’ll need to know the width of your baluster, the width of the gap you want between your balusters, and the width of your posts that your rails attach to.


How to Calculate Baluster Spacing on Steps

While baluster spacing on a deck rail is more straightforward, putting balusters on steps is also easier than it looks if you know where to begin.

Remember that stair treads have to be a minimum of 10” wide – some New England states allow 9”, but for this article, we’ll assume it is 10” where you live.

Calculate Stair Baluster Spacing Yourself

  1. Determine the exact width of your stair tread.
  2. Mark the middle point of the tread – do not count the lip of the tread that overhangs the riser.
  3. Place your first baluster at the edge of the tread, flush with where the riser meets the tread.
  4. Your second baluster’s front edge will sit on the middle mark of the tread.
  5. With two balusters per tread, you can do your entire stair railing in this manner.

When calculating spacing on the top rail for those balusters, simply lay the rail flat and mark off every gap. If the gap between your balusters is 3”, and your balusters are 2” side, then mark off every 5” on the top, flat face of the rail. When you affix the rail between your two posts, you’ll know to fasten the outside of the baluster edge to that mark.

Baluster Spacing on Steps

Also, ensure your railing is at least 3’ from the top of the railing to the nose of one of the stair treads.

Stair Baluster Spacing Example

Let’s say you have a tread width of 11”. Your balusters are 2” wide pickets.

If we divide that tread in half, we get 5.5”. Putting our first baluster at the front of our top stair tread, we then put our second baluster on the same tread at 5.5”, where the front of the baluster sits flush with the center mark.

With our first baluster at the front of the 11” tread, and sitting 2” wide, the measurement from 9” to 5.5” is 3.5” – more than enough space to meet code.

If you have extra-wide treads on your deck steps, you’ll have to put three balusters per tread, in which case you would just divide the width of the tread by three. That would tell you the distance between the front of each baluster starting at the baluster at the front of the tread, flush with the riser below it.

Understand that this section is only relevant for stairs that have balusters that attach to a top rail and the stair stringer. If you are using a prefabricated kit, then you don’t have to worry about where to put your stair balusters – it’s already done for you.

If you are using a kit, make sure that a 6” sphere can’t pass between the area under the bottom rail, where the tread meets the bottom of the riser. If so, you’ll have to lower your bottom railing on your stair railing system.

Deck Baluster Spacing Using a Template

There are many ways to space your balusters evenly along your deck railing. Let’s take a look at several different ways you can go about accurately measuring out your balusters for a uniform appearance.

  • Use a measuring tape. This is the simplest and most reliable way to space your balusters. Once you know your baluster width and desired spacing, add the two together. If the total is 4.5”, then put a mark along the rail every 4.5”. The front of each baluster will sit on that mark.
  • Use a 2×4. If you aren’t too picky, then a 2×4 – or 2×3 depending on the look you want – will work for baluster spacing. Just be sure to use it at the top and bottom of your baluster when fastening.

For instance, hold a 2×4 flat, perpendicular to the baluster so that it is between the previous baluster and the one you are installing. Repeat at the top of that same baluster – this method ensures both the top and bottom are 3.5” from the previous baluster.

A general rule of thumb is that the spacing of balusters should be about 1.5 times the width of your baluster. So if you have 2” balusters, then a 3” gap is aesthetically pleasing.

Spacing Different Types of Balusters

Spacing deck balusters that are a material other than wood is no different. Specialty balusters that have a pattern, where the balusters alternate between straight and profiled, will usually come with installation instructions.

If not, remember that the furthest gap between two profiled balusters must still be only 4”. In other words, there cannot be any space between your profiled deck balusters more than 4”.

Spacing Horizontal Deck Balusters

Horizontal deck balusters are increasingly popular these days, as I see more and more popping up around where I live.

The same rules apply to these types of balusters – no gap more than 4” apart, with a maximum spacing of 4” from the top of the deck boards, and a minimum of 36” high for the entire railing.

To calculate the number of horizontal balusters you’ll need, use the same formula we used for vertical balusters with one major change. Instead of measuring the length of your railing, you will measure the height of your railing post. Here’s how:

  1. Find your total railing post length – total post length should be to your desired railing height, in inches.
  2. Divide that number by the width of your baluster plus the width of your gap between balusters.
  3. The answer is the number of balusters you’ll need.

Let’s say your horizontal baluster is 3” wide, and you want a gap of 3.5” wide. You only want a minimum height of railing – 36” high.

Add your gap and baluster width = 6.5”. Divide your railing height, 36”/6.5” = ~5.5. Since you can’t have half a baluster, you’ll need 6 total, and you can use a table saw or circular saw to cut the last one to keep your railing height at 36”


Deck balusters are first and foremost a safety item on your deck and should be fastened and spaced according to code. Don’t space your balusters 4” apart, even though code says this is allowed. Over time, balusters can warp, shrink, or twist out of shape, resulting in larger gaps. Shrinking these gaps during installation by a quarter or half an inch can save you tons of trouble in the future.

Thanks for taking the time to peruse this deck baluster spacing guide. As always, if you have any suggestions for content that you think could make this guide better, then please don’t hesitate to comment below or drop me a line. And of course, best of luck with your next deck baluster and railing project!

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