Drill Bits Metric Vs Imperial: Which Drill Bit Size System Is Better?

Last Updated on July 9, 2022

If you are considering buying drill bits for your project, you will need to know which ones are metric and which are imperial. Listed below are the typical fractional drill bit sizes.

The fractional sizes are the most commonly used in masonry drilling, rotary hammer drilling, and rotary core drilling. Depending on your needs, you may want to try drilling a few samples of each before you make your decision.

Typical fractional drill bit sizes

Drill gauge sizes in North America are denoted by letter or number sizes. They are not the same size as their metric counterparts. Instead, the letters represent the actual size of the drill bit.

For example, the largest letter size is “A”, the next largest size is “B”, and so on. Similarly, letter gauge drill bit sizes go from “A” to “Z.” The chart below gives the equivalent size in metric and imperial units.

Typically, letter and number bits are smaller than metric and are traceable to nineteenth-century English wire gauges. These are slightly smaller than their imperial counterparts, and offer incremental differences in drill diameters.

While the differences aren’t significant when drilling wood, they can be convenient in metal drilling. But how can you determine which drill bit to use? Listed below are some common differences between metric and imperial sizes.

The difference in metric and imperial sizes between drill bits is more confusing than it seems. While imperial and metric are the most commonly used measurements, drill bit sizes are classified by size. Some sizes overlap, such as 1/8″ or 1/64″. For example, a drill bit size of one inch is described as a “B”.

Typical fractional drill bit sizes are a result of a standard sizing system. In the imperial system, drill bits are sized in 1/64-inch increments, while metric sizes are based on the diameter of the solid metal shank.

Typically, fractional bit sizes are used when drilling through very thick materials, such as masonry. Electrical professionals often use long bit sizes to drill through finished walls to run wires.

Typically, a metric drill bit size is defined by its diameter in standard metric lengths. Likewise, standard sizes are defined by standards organizations. The British Standard BS 328 specifies 230 sizes, ranging from 0.2 to 25.0 mm.

The smaller size corresponds to a smaller tolerance for the drilled hole’s diameter. For this reason, designers generally want the size of the drill bit to be within 10% of the arbitrary hole size.

Despite the differences in measurement systems, metric drill bits are compatible with imperial drills. Metric drill bit sizes have many advantages over imperial drills, including more precise hole sizing.

Furthermore, you can purchase metric drill bits even in the U.S., and many are listed on packages as metric sizes. It’s a good idea to read the metric size of the drill bit before you purchase it.

Typical fractional drill bit sizes in masonry drilling

Typical fractional drill bit sizes in masonry drilling

Depending on your project, you may need to use bits that range from 1/64 to 1/64 inch. A 29-piece drill bit set is ideal for a variety of disciplines. A typical fractional drill bit size chart is provided below for reference.

This chart includes the standard sizes of drill bits in a variety of diameters. Occasionally, specialty fasteners will require bits that are not available in standard sizes.

Typical fractional drill bit sizes in a masonry drilling project are 1/8, 3/8, and 5/16 inches. Drill bit manufacturers also use fractions of an inch to specify the size of the bit. Some manufacturers use letters to specify the size of the bit, as well.

Depending on the material and application, there are drill bits that are designed for wood, while others are designed to drill through tougher materials such as masonry.

These tools are compatible with both hand and power units. While they are not as durable as masonry drills, a good drill bit set should contain more than one common size drill bit.

For maximum safety, always wear a dust mask and always use a protective respirator to protect your lungs from fine particulates. You can also buy a high-quality drill bit set from a drill store that sells screwfix masonry bits.

Typically, fractional drill bits are smaller than their metric counterparts. In fact, fractional drill bits are used for tapping purposes. A fractional bit of one inch will be equivalent to the next larger fractional size of the same drill bit.

However, the size of a fractional drill bit will have a major impact on the overall drilling job. For example, a #7 bit is 0.2010 inches in size, which is equivalent to three sixteenths or thirteen/64 in fractional measurement.

Typically fractional drill bit sizes in masonry drilling are indicated by small markings on the drill bit’s threads. They typically indicate the diameter in fractions.

Some bits have a self-starting feature, while others come to a point. A self-starting drill bit has a blunt tip, while some are symmetrical. It is important to understand that a drill bit’s markings can be misleading. If you’re not sure which size drill bit you need, talk to a professional about the proper tool for the job.

Another common mistake in masonry drilling is using too-large a bit. Too-large a drill bit can cause a blunt bit. This isn’t the best way to drill. When you lean on a bit too hard, it will break. Moreover, excessive pressure on the drill bit will cause it to overheat and break. And that’s not something you want to happen.

Typical fractional drill bit sizes in rotary hammer drilling

In rotary hammer drilling, drill bits are available in a variety of sizes. Drill bits can be found in sets from 1/16 to 1 27/64. Fractional sizing refers to the size increments of whole, half, quarter, eighth, sixteenth, and sixty-fourths. Fractional drill bits in larger sizes are generally available in sets of 29 sizes or more.

The flute and helix angles are also important factors in determining drill bit size. The SDS BOOSTER MAX HEAD is designed with six cutting edges and a one-hundred-degree split point, making it suitable for most rotary hammer drills.

Its self-centering tip helps prevent over penetration. The KVS BOOSTER MAX HEAD also features six cutting edges, enabling the user to drill harder and faster without walking.

Different tasks require different sizes and types of drill bits. Despite their versatility, not all sizes are available. The most common sizes include 3/8 inch and 1/2-inch. Most fractional drill bits are equipped with open tips, which help the user to grip them while drilling.

These bits can be used on both hand-held brace-and-bit and power drills. For drilling wood, the Vermont American high-speed standard-length fractional bit is an excellent choice. The drill bit’s 118-degree point allows for fast start-ups, and the bit’s durable design makes it a versatile choice for drilling in most materials.

The SDS-Plus rotary hammer bit features grooves on its shank, which lock the bit in place. They can also move back and forth independently, making them easy to insert and remove.

Some of the big brands feature proprietary systems and SDS-Max chuck systems, so it’s important to match the bit with the drill mode. This drill bit set is versatile and includes many of the common sizes.

Depending on the material, the high-speed steel rotary hammer bits may be used for general-purpose drilling. These bits are durable and suited for drilling in wood, metal, and plastic. These drill bits are hardened for superior performance in demanding applications.

They also prevent walking when drilling. In addition to this, they have excellent heat dissipation properties. The higher the quality, the more expensive the drill bit set should be.

Typical fractional drill bit sizes in a rotary hammer’s range are listed in pounds of impact energy (amps) and maximum hole size recommended by the manufacturer.

Although rotary hammers are capable of drilling larger holes, most are designed for drilling seven eighth-in. holes. Consequently, if you only need to drill seven-eighths-in. holes, go for a higher-quality rotary hammer drill.

Frequently Asked Questions (FAQs)

– Which one is better, metric or imperial drill bits?

It depends on the specific application. Generally speaking, metric drill bits are better for smaller holes, while imperial drill bits are better for larger holes.

– Why are there two systems for measuring drill bits?

Metric drill bits are made to the International System of Units, or SI, which is the modern metric system. Imperial drill bits are made to the British imperial system. There are a few key differences between the two systems.

The most obvious one is that metric drill bits are measured in millimeters, while imperial drill bits are measured in fractions of an inch.

– How do you convert from metric to imperial drill bits?

To convert from metric to imperial drill bits, you first need to know the conversion factor. The conversion factor is 1 mm = 0.03937 inches. Once you have the conversion factor, simply multiply it by the measurement in millimeters to get the measurement in inches.

For example, if you want to convert a drill bit that is 3 mm in diameter, you would multiply 3 by 0.03937 to get 0.1181 inches.

– How do you convert from imperial to metric drill bits?

To convert from imperial to metric drill bits, you first need to know the conversion factor. The conversion factor is 1 inch = 25.4 mm. Once you have the conversion factor, simply multiply it by the measurement in inches to get the measurement in millimeters.

For example, if you want to convert a drill bit that is 0.5 inches in diameter, you would multiply 0.5 by 25.4 to get 12.7 mm.


Some people prefer metric drill bits because they are easier to find and because most drill presses are designed to use metric drill bits.

Others prefer imperial drill bits because they are more precise and because they offer more options in terms of sizes. Ultimately, it is up to the individual to decide which type of drill bit is best for their needs.

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