How to Measure Drill Bit Size

Wondering how to measure drill bit size? As far as drilling is concerned, having the right size bits is essential. If you’re planning a DIY project that involves bits and screws, you will need to get as accurate as possible. Using bits that are too small can result in a cracked or damaged workpiece, stuck bits or screws and even a damaged drill if you try and force a screw into a hole that does not fit the screw you are driving to drive into your workpiece. On the other hand, a bit that is too large means that you will have to change the size of your screws, which can affect the measurements of your entire project. 

The biggest problem with guesstimating the size you will need is that you cannot be 100% sure that you have the right size bit. Accuracy is everything with any type of drilling, whether it is small DIY jobs around the house or larger renovation projects. To make sure you always get the right size drill bit for the job at hand, we’ve put together a few tips.

Measuring Drill Bit Sizes

Here are a few ways that you can measure drill bit sizes to ensure that you have the right size for your project.

Check the screws or fasteners

The easiest way to see which size you need is to check the size of the screw or fastener. This will be easier still if you are buying new sets of screws and bits at the same time. Take a loose screw and compare it to the size of the bit you need to use, using the screw’s core rather than its flute. A bit that is very slightly smaller than the screw will ensure a proper fit. Choosing a bit that is too small means that the screw will get stuck so take care to choose carefully. For a fastener such as an anchor, you will need to use a bit that is the same size as the anchor’s body. The bit needs to be big enough to drill a hole into the wall, while still being small enough to easily insert the anchor by hand rather than using your drill. To measure the size, hole your drill next to the anchor and measure the distance from the bit to the end of the anchor.

Use an adjustable wrench

An adjustable wrench will make things easier. If you are trying to figure out the size of your bit to choose screws to match, you can do so with a wrench. Hold the bit you plan to use and carefully close the wrench until the jaws on either side where the numbers of the bit are printed. When they stop touching, you will have an accurate idea of size. This method is also a great option if you have a selection of bits in your toolbox and aren’t sure of the size. Once you’ve measured your bit, you can easily measure your screws. 

Invest in callipers

This tool is a must-have for your toolbox, giving you a high level of accuracy when measuring screws, bits and the dimension of any object. Using this tool will give you a precise measurement of the screw and the bit, making it easy to match with precision. They come in two forms - standard and digital. With two jaws at the top, the bottom jaw slides up and down to measure the dimension of the screw. Place the body of the screw between the jaws and then push the jaws shut with your fingers. Make sure that you don’t measure the head of the screw as this will give you an inaccurate measurement. Once the jaws are in place, you will get a measurement in millimetres. Digital callipers make things even simpler, giving you a reading on a digital screen. From there, you can match your screws and bits.

Make test holes

It can also be useful to make test holes to match up screws and bits to get your sizing right. This is helpful for future sizing as well. Use a thin piece of sheet metal and make a hole through the material using the bit you aim to use. You can then place your screws into the hole until you find one that fits properly. You can also keep this sheet somewhere safe to test sizes for other projects down the line. This is a good option if you have a lot of loose bits and screws and can’t remember their sizes. 

Invest in drill bit sets

Finally, it is always a good idea to invest in a set of bits. Most sets include standard sizes as well as larger or smaller sizes. Depending on the bit you are using, the size of the hole you need to make and the screws or fasteners you need to add, a set will give you more room to test sizes without having to go back and forth to your hardware store. Reading selection charts on bits and screws is also essential. 

With a huge variety of bits for every material and project, Ruwag has all the drill bits you need in one place, making it as easy as possible to get your project underway.