How to Cut a 4×4 with a Circular Saw?

Cutting a 4×4 post is one of those tasks that seems easy, but unless you have the right tools is actually tricky to get right. Standard circular saws with 7 ¼” blades can only cut 2 ½” deep, so making the cut in a single pass isn’t possible.

That means you’ll need to make multiple passes to cut clean through the 4×4, and this can result in a poor finish unless you take steps to ensure your cuts line up perfectly with each other. There are several methods to accomplish this, so let’s take a look at a few ways to cut a 4×4 with a circular saw.

Tools & Materials

  • Circular saw
  • Marker or pencil
  • Clamps
  • Drill/driver
  • Scrap plywood
  • Speed square
  • Hand saw or reciprocating saw (optional)
  • Sandpaper or sander

Cutting a 4×4 with a Circular Saw – Guide

If you need to cut a 4×4 post, then the ideal tool is a large 12” miter saw. This saw has the blade diameter needed to chop through a 4×4 in a single pass, so if this is an option for you it’s the way to go.

A miter saw isn’t always an option though; if you need to cut a 4×4 on the job while you’re installing fence posts then a circular saw is a better option, as it can cut through a 4×4 in 2 or 3 passes, and is far more portable than a 12” miter saw.

Circular Saw Only Method

This method offers a good compromise between speed and accuracy. You only need one saw to complete the cut, and using the initial groove as a guide typically results in a nice clean finish.

Step 1: Mark Cut Line

The first step is to measure and mark your cut line onto the 4×4. Use a speed square and pencil to mark your initial line along the side of the 4×4.

4x4 with cut lines drawn
4×4 with cut lines marked on it.

Then flip the 4×4 over and repeat this step on each of the four sides. You want to be careful and deliberate while doing this as these will be your guidelines while cutting through the 4×4.

Step 2: Make the First Cut

First, make sure your circular saw is adjusted to the maximum cutting depth. This will ensure you can complete the cut in without having to cut through all four sides.

Line up your saw’s blade with the cut line you drew in the previous step. To be on the safe side, try to make the cut on the waste or scrap side of the cut. This will ensure that the cut will err on the side of too long instead of too short.

cutting 4x4 up close
Making the initial cut.

You can always go back and shorten it if needed, but you can’t add back extra material.

Use your speed square as a cutting guide by butting the edge of your saw’s shoe up against it. If you want the cut to be perfect, clamp the speed square to the 4×4 rather than gripping it in your hand.

Then run your saw along the 4×4 in line with the cut line.

Step 2: Rotate the 4×4 and Make the Second Cut

Unclamp the 4×4 from your workbench, and rotate the 4×4 90° (one turn). Your initial cut will leave a 2 ½” deep groove that you can use as a cutting guide for the remaining cuts.

groove in 4x4
Here you can see the groove after making the initial cut.

Line up your saw with the cut line from step 1, slide the blade in the existing groove, and complete the second cut. You shouldn’t need a speed square or other guide for this as your basically cutting along the existing groove.

You might be wondering why not flip the 4×4 over to the opposite side (180°) and finish the cut in two passes?

Because you won’t have an existing groove to use as a guide, it’s more likely to result in an uneven finish.

Step 3: Rotate 90° and Make Third Cut

Finally, rotate the 4×4 another 90° and complete the third and final cut. After the first two cuts, there will only be a small piece of lumber remaining to cut through, so this should be effortless.

Simple Jig Method

This method is similar to the above method; it uses a few pieces of scrap plywood as a cutting guide instead of a speed square. If you’re not that familiar with using a circular saw, then this method is a good way to go as it’s more or less foolproof.

Step 1: Mark Cut Line

Just like the above method, the first step is marking your cut line on the 4×4. Use a ruler, square, or scrap piece of wood to mark your desired cut line with a pencil.

Then flip the 4×4 over and repeat this on all four sides.

Step 2: Create Simple C-Shaped Cutting Jig

Next, you’ll want to create a simple C-shaped cutting jig using scrap wood. The jig consists of three pieces of scrap plywood cradling the 4×4 with each one measuring 3 ½” long – the same width as a piece of 4×4 dimensional lumber.

Use your cut line as a starting point, add to it the distance between your saw’s blade and the edge of the shoe and make a second mark in parallel with the first. This is called the offset line – and accounts for the width of your saw’s shoe.

Use a 3 ½” section of plywood to create the first portion of the C-shaped jig. Line it up with your offset line and attach it to the 4×4 using a few wood screws.

Then repeat this on either side of the first section of the jig until you have a C-shaped jig cradling the 4×4.

Step 3: Make Your Cuts

Now, all you need to do is butt the edge of your circular saw against the side of the jig and cut through the 4×4. The jig will ensure you cut completely straight and makes cutting a perfect finish nearly effortless.

Flip the 4×4 over and repeat this cut with your circular saw on all three sides of the 4×4.

Then use a drill to remove the screws holding the jig in place, and you’ve got yourself a perfectly cut 4×4.

Circular Saw & Hand Saw Method

This method is more of a quick and dirty method, making it ideal when you’ve got a bunch of 4x4s that need cutting quickly. It might not result in a perfectly clean finish, but it’s fast and doesn’t require you to rotate the 4×4 at all.

Step 1: Mark Cut Line

Just like the other methods, the first step is to mark your cut line on the 4×4 using a pencil and speed square.

In this case, we are only going to make a single cut line, so there’s no need to flip the 4×4 over and mark additional lines.

Step 2: Make Initial Cut

making the initial cut
Making the first cut.

Next, line up your circular saw’s blade with the cut line, and make your initial cut along the line on the waste side. Use a speed square or piece of scrap wood as a guide if you’re worried about cutting accurately.

Step 3: Use Hand Saw to Finish the Cut

Now you’re left with an approximately 2 ½” deep groove in your 4×4 that needs to be cut all the way through to complete the cut.

Slide your hand saw’s blade into the existing groove, and carefully finish the cut by hand. This will require a little muscle and elbow grease, but as long as the 4×4 is firmly clamped in place it shouldn’t be too difficult.

finishing the cut with a reciprocating saw
Finishing the cut with a reciprocating saw. This allows you to make the entire cut without needing to rotate the 4×4.

An alternative to this would be using a reciprocating saw instead of a hand saw. This will make the task a bit faster, but will likely result in a rougher finish than a hand saw will.

How to Cut 4×4 Posts That are Already Mounted?

What do you do if you’ve got a 4×4 that’s already mounted in place vertically?

This is often the case when you’re installing fence posts in concrete, as you don’t know precisely how the post will settle in place, so it’s easier to set them first and cut them afterward.

In this case, the above methods can be a little tricky, especially if you need to hold the saw above your head to reach the cutting area. These methods can still work, but using a c-shaped guide will be easier than using a cut line to guide your cuts.

If that’s not an option, and you don’t need a perfect finish, then a chainsaw can also work well for cutting fence posts to your desired length. If you’re going to put a fence post cap on it afterward, then a perfect finish isn’t necessary anyway.

Denis Gardner

I've loved tinkering and fixing things for as long as I can remember. So, naturally, I gravitated towards DIY and home improvement when I bought my first home. Nowadays you can find me writing about my passions or messing around with my newest tool!

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