Some countries use metric units while others use imperial to define length and distance. In a globalized world, it's important you know how to convert between them, and fast.

    Want a secret weapon you can use to get the job done right every time? Try our mm to inches calculator. It works with more than 60 length units and provides results up to six decimal places.

    If you are wondering how many inches are in one mm, the answer is 0.039370. To easily convert your millimeters to inches you can divide your starting number by 25.4.

    In the guide below, we're going to teach you how to convert from mm to inches and inches to mm. We'll also answer some common questions about the origins of both measuring systems.


    What can this unit converter do?

    Our unit converter does just what it says. It's a pre-programmed calculator that converts from one unit to another. It does this quickly and precisely.

    When would you use it?

    Let's say you've measured your windows for curtains using centimeters and millimeters. When you get to the fabric shop you find they sell material in feet and inches.

    That's when you can look at an online unit converter on your smartphone. And use it to convert your metric measurements into imperial, or the other way around. Life-saver huh?

    Why convert mm and inches?

    Converting between millimeters and inches is a common practice when working with materials or tools.

    Different industries and different suppliers may measure with a unit of length different to yours.

    Our tip is to list each item you measure in both units to avoid error and save time.

    And, should you have to do unit conversions, make good notes of how you got to your final figure. These sorts of records can save a lot of time and headache later.

    How do you convert mm to inches (and vice versa)?

    Millimeters to Inches

    1 millimeter is equal to approximately 0.039370 inches. The conversion is a simple multiplication, expressed in the following formula:

    Inches = millimeters x 0.03937

    Solved Example

    You have 16 mm and you want to convert to inches.

    16 x 0.0393700787 = 0.6299212592

    Another simple way to convert mm to inches, is to divide your starting number by 25.4. This is the amount of millimeters in one inch.

    16 / 25.4 = 0.6299212598

    The answer should be 0.6299212592 inches, which we would round out to 0.629921.

    Inches to Millimeters

    To convert from inches to millimeters, the process is similar, with a different multiplier. We know an inch is 25.4mms. See the equation to convert below:

    Millimeters = inches x 25.4

    Solved Example

    You want to know how many millimeters there are in 4 inches.

    4 x 25.4 = 101

    The answer you get is 101 mm.

    If you'd like to save time and guarantee precision, better yet - use an online calculator. Also, be sure to check out our handy conversion table.

    What is a millimeter?

    A millimeter is a unit of length equal to one-thousandth of a meter. The prefix of 'Mille' is Latin for 'one thousandth'.

    It is part of the metric system of measurement alongside things like meters, grams, seconds, and amperes.

    The metric system is a base-ten system. That means you can convert between metric units by multiplying by 1000, 100, or 10, and so on.

    This system is accepted internationally as a decimal system of measurement. It is part of a set of base units also known as the International System of Units (SI).

    The Meter

    The meter is defined as 1/299,792,458 of the distance that light covers in a second. A millimeter is one-thousandth of a meter.

    By multiplying this distance-of-light figure by 1,000, we get the technical definition of a millimeter.


    The millimeter is used for small lengths. Or in situations calling for great detail in longer lengths, such as in industrial design.

    A standard ruler measures 300mm. The millimeter is generally the smallest unit of measurement of a metric ruler.

    Compared To Inches

    A millimeter is equal to approximately 0.039370 inches.

    What is an inch?

    An inch is equal to 2.54 cms but belongs to a different measurement system.

    The inch measurement belongs to the imperial system of measurement, along with feet and yards. There are 12 inches in a foot, and 3 feet in a yard.

    Where did the inch come from?

    The urban legend on this one says that the inch was originally the width of a man's thumb at the base of the nail.

    Even today, in many languages the word 'inch' is like that language's word for 'thumb'.

    In the 14th century, it was defined as three corns of barley placed end to end. Barley from plant to plant can vary just as much as a thumb varies between people.

    So even with this change, it remained an imprecise and inconsistent measurement.

    Do you agree with those who think the US could trade and share information globally more effectively if it adopted the metric?

    American manufacturers had designed high-end machines and tools based on inches, around the 1870s. They argued that changing to metric with the rest of the world would be too expensive.

    So the system was never fully adopted. America today uses a hybrid system where either measurement is acceptable.

    When were measurements first recorded?

    The first records of measurements come from the 3rd or 4th millennium BC.

    Civilizations needed a common language of measurement. Especially for things like trade, agriculture, and construction.

    Initially, the system of units was specific to trade routes or products.

    The way to gauge an amount of grain had little to do with the measurement used to gauge an amount of milk, and so on.

    So while the differences in measurement units today are frustrating, remember it was once much more complicated!

    With the industrial revolution came the need for exact measures. To trade more precisely, and for scientific experiments also.

    It was for this reason that the 18th century saw a measurement system become standardized.

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