Converting between millimeters (mm) and inches is essential in fields like engineering, manufacturing, and even for everyday tasks around the house. You might need to figure out how to convert one unit to another, even if you’re just trying to figure out what size drill bit to buy.
The metric system (SI) and the Imperial/US customary system are the two most common systems of measurement. This guide will give you a clear and simple explanation of how to convert 9mm to inches.
But let’s get specific: we’re going to show you exactly how to convert 9mm into inches, and we’ll even break down the fractional representation so you know what to do with your conversion.
Millimeters and inches defined
To understand exactly how 9mm translates into inches, it helps to understand the basics of each measurement system.
The millimeter (mm)
A millimeter is a unit of length in the metric system. There are 1,000 millimeters in a meter.
Millimeters are used all over the world in a variety of industries. They’re often used when precise measurements are needed, such as when measuring small components for electronics or specifying the sizes of camera lenses.
The inch (in)
An inch is a unit of length in the Imperial and U.S. customary measurement systems. Today, the inch is mainly used in the United States.
There are 12 inches in a foot and 36 inches in a yard. Inches are commonly used to measure things like the size of a screen or the diameter of a pipe.
Conversion Formulas and Methods
Here’s how to convert millimeters to inches, and inches to millimeters.
Converting Millimeters to Inches
The formula you’ll want to use is 1 mm ≈ 0.03937 inches. To convert from millimeters to inches, divide the number of millimeters by 25.4.
In the case of 9 mm, the calculation would be: 9 mm / 25.4 ≈ 0.35433 inches.
So, 9 mm is about 0.35433 inches.
Converting Inches to Millimeters
If you’re converting the other way, 1 inch = 25.4 mm. In that case, you’d multiply the number of inches by 25.4.
Rule of Thumb
For a quick estimate, just remember that 100 mm is about 4 inches. Of course, this is just a rough estimate, but it may be useful in a pinch.
9mm in Inches: Decimal and Fractional Representation
As we’ve seen, 9 millimeters is about 0.35433 inches. While that’s precise, long decimals aren’t always the most practical thing to use in everyday situations. It’s pretty common to round those decimals off for simplicity’s sake.
In certain fields, like construction and woodworking, it’s often more useful to express measurements as fractions. So, how do we turn that decimal into a fraction?
One way is to use a fraction calculator. You can also approximate it. Either way, you’ll find that 0.35433 inches is just about equal to 11/32 of an inch. (You could also express it as 9/25.4 in fraction form, but that’s not usually done.)
So, to sum it up, 9mm is approximately 11/32 of an inch.
When is this conversion useful?
Knowing that 9mm is roughly equivalent to 3/8 of an inch can be surprisingly handy.
For example, if you’re drilling a hole and need a bit close to 9mm, a 3/8-inch drill bit will usually do the trick. It’s also essential when you’re talking about firearm calibers, where measurements can switch between metric and imperial.
Keep in mind that accuracy is important. While “close enough” works in some cases, critical applications demand precision. Using the wrong conversion can have serious consequences.
Putting It All Together
So, there you have it: 9mm is equal to 0.35433 inches, or about 11/32 of an inch.
Whether you need the decimal or fractional equivalent depends on what you’re doing. Use whichever measurement works best for your particular project. And remember, use the information here to convert accurately!