How to Determine Drill Bit Size for Screw

Although it might seem just a small part of the whole building process, choosing the drill bit size can reshape everything. Drill bits are basically the foundational blocks of a building project.

If you’re a beginner using drills, there are a lot of things to learn about drilling. It can feel a bit overwhelming at the beginning to find the correct drill bit size.

Drill Bit Size for Screw

When you’re doing a project requiring drilling and pre-drilling, you ought to know how to determine drill bit size for screw. In this article, we’ll explain how you can do this like a pro.

Do You Need To Drill Pilot Holes For Wood Screws?

It is a common mistake of many novice woodworkers to drill screws into the wood without creating a pilot hole first. When you have a pilot hole the screw can travel much easier with less friction through the surface. It also poses a much lesser risk of cracking the wood.

You want to choose the correct drill bit size to correspond with the pilot hole. Although choosing the right sized one isn’t a very difficult thing to do, picking the wrong size may split the board or create too large a hole. As a result, the screw won’t have enough wood around its shaft to hold onto.

Read More: Best Self Centering Drill Bit

How Do I Choose The Right Size Drill Bit For A Screw?

With seemingly endless fractions and decimals used for screw sizes, it is a great challenge for a beginner to choose the correct size. How do you supposed to know exactly which size you need?

There are other methods that can help you pick the correct sized bit other than looking at the size chart. All you have to do is to follow our suggestion below:

Method 1 – Take the screw that you want to use after drilling and place it next to the drill bit. Line both of them up end to end and check with your eyes if both have the same width. Don’t take into account the threads of the screw. If the width of their shaft is the same then the drill bit is probably of accurate size.

Method 2 – if you’re going to use washers, on the other hand, that requires that the screw is a bit loose, then do the opposite of the previous suggestion. That is, while lining the screw and the drill bit, make sure that they both have the same width including the screw threads. This will not make the screw seal too hard against the surface and allow you to use the washer.

Related Article: Drill Bits Size for Wall Anchor

Drill Bit Sizes for Drilling Screw Pilot Holes

Once you’ve chosen the correct drill bit, it is time to drill a pilot hole. A pilot hole enables you to guide the screw where it needs to go. Without making a pilot hole before drilling, you can cause the wood to chip, splinter, or possibly break.

The right size of the drill bit will depend on the screw size. You can pick the correct one either with the help of a drilling chart or through measuring by your eye. Drill bit to screw size chart is shown below:

Screw SizePilot Hole Size for HardwoodPilot Hole Size for Softwood
#41/16″      3/64″

Frequently Asked Questions

Should a drill bit be the same size as a screw?

If you want to stick the screw tight in the hole then the drill bit size has to be equal to the screw shaft’s width minus the threads. You can do this by simply lining up both the bit and the screw next to each other and measuring with your eyes.

How much smaller should a drill bit be than the screw?

The size of the drill bit compared to the screw depends upon the purpose for which it is to be used. If you want to make a pilot hole then it has to be less than that of the thread diameter of the screw but slightly larger or the same as the core size. This is because you want to drive the screw inside smoothly without splitting the wood.

For tap size, it has to be smaller than outer thread size but slightly larger than inner thread size.

How do you tell what size a screw is?

Usually, the size of the screw is engraved on the screw itself. But sometimes it is not written there then what do you do? Simply eyeball it with the drill bit.

Just hold the drill bit directly in front of the screw and compare their sizes. If you see the width of the drill bit is the same as the central column of the screw, excluding the teeth or spirals. You only need to pick the drill bit that has the same size as the central column and not the spiral.

Related Article: Tap Drill Size Chart


Drill bits are tricky to pick as they have so many different sizes. Choosing a bit that has a slightly off size than the screw can make a massive difference in the end. That is why you need to know how to determine drill bit size for screw properly so as not to make mistakes.

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