What size nails for trim? Here is what you need to know

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This guide answers the question of “what size nails for trim?”

Read to the end if you have been unsure about what size nails work best for trim…

What size nails for trim? A simple guide and what you must know

To start us off, below is a simple guide that is helpful in choosing the best nail sizes for various nailing tasks:

23-gauge nails

These work best for small painted/stained moldings.

To be clear, these nails are usually used to hold the materials together while the applied adhesive sets/cures.

21-gauge nails

These are best suited for fastening the following:

  • Small painted/stained moldings
  • Medium to small casings
  • Attaching chair rail


18-gauge nails

The best projects to use 18 gauge nails for are:

  • Medium to small casings
  • Fastening chair rails
  • Nailing low-profile crown molding

16-gauge nails

You can comfortably use 16-gauge nails for the following tasks:

  • Nailing casing (through drywall) – 16ga nails can be used as the outer nail on the casing.
  • Nailing base trim (or other large trims)

15-gauge nails

15 gauge nails are recommended for almost the same jobs as 16-gauge nails.

Specifically, these nails are most appropriate for:

  • Nailing casings (through drywall) – they can be used as the outer nail on the casing.
  • Nailing base trim (or other large trims)
  • Installation of door jambs (especially heavy, solid-core doors).

So to answer your question “What size nails for trim?”, the best choice is 15 or 16-ga finishing nails (keep in mind that 15-ga nail diameter is thicker than 16-ga).

Don’t forget that nailers that are typically designed to shoot the fattest trim nails are those that generally fire 15 to 16-ga nails.

The other question is, of course, what is the right nail length is best for trims?

Now, you can attach trim strongly enough with any 15 or 16-ga finishing nails with a length of between 1 1/2-inch to 2 1/2-inch (4D to 8D nails).

Let us look at the issue of length more deeply:


What is the best size nail for trim?

We are onto the question of length and as I have just mentioned, the suitable nail length range from 1 1/2-inch to 2 1/2-inch(4D to 8D nails)..

Needless to say, a lot of you want to know exactly what the most suitable nail length is so here is what you should do:

Apply the following rule of thumb:

Important rule of thumb

If you’re uncertain about the best nail length, just check the thickness of the trim material you want to nail and apply the rule of thumb hereunder:

Now, it is broadly recommended that nails be (at least) 3 X the thickness of materials being nailed.
For instance, for any 1/2″ thick trim material, you should use a nail that’s 1-1/2″ long (1/2″ times 3 will give you 1.5”).

Likewise, use 2.25” long finishing nails for 3/4-inch baseboard trim (0.75″ multiplied by 3 will give you 2.25”).

That way, you can easily select the best nail length to use for your project.

Just bear in mind that generally, 1 1/2-inch finish nails (4D) are ideal for installing thin trims while the fatter 2-1/2 inch nails are the best way to go when nailing thicker trim materials.

You are free to choose anything else in between depending on the width of your trim.


Using 15 ga nailer vs 16 ga nailer

Either a 15-ga nailer or 16-ga nailer can be perfect for trim jobs.

However, 15-gauge nailers have one major advantage..

They have an angled nose which makes nailing in corners and other tight spaces easier compared to 16-ga nailers (these have a straight nose).

Here is the most important thing: Use a 15-gauge nailer if you are fastening trim that is 1-inch or more thick otherwise a 16-gauge nailer should work fine.


Can I use 18-gauge nails for trim?

Yes you can but there is one major downside: These are narrower and won’t have the greatest holding power (compared to 15 ga and 16 ga nails).

So you should only use them for smaller trims up to ½”– doing that is quite okay particularly because they tend to leave a smaller hole compared to 15 ga and 16 ga nails).

Remember you will need to have a brad nailer if you want to shoot 18-ga brad nails.


What size nails for trim- summary

Before I go, here is a recap of the most important bit of the article:

The best nails size to use for trim is 15 or 16-ga finishing nails with a length of between 1 1/2-inch to 2 1/2-inch (4D to 8D nails).

To reiterate, the ideal length boils down to the thickness of your trim pieces..

For example, when fastening ¾-inch base trim over drywall, 2.25-inch 16ga nails works well

You can as well use 18-gauge nails, 1 1/2-inch for smaller trims up to ½”.



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