How to Convert Inches to Millimeters: 14 Steps (with Pictures) (2024)

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Co-authored byDavid Jia

Last Updated: May 26, 2023

Convert Inches to Millimeters

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1. 1

   Understand the relationship between inches and millimeters. One inch is internationally accepted as being equivalent to 25.4 millimeters.^[2]

   • Written as an equation, this relationship is represented as: 1 in = 25.4 mm
   • This official, standardized measurement has been set on international records since 1959.
   • Both inches and millimeters are units of measurement. Inches belong to the English system of measurement, while millimeters belong to the metric system of measurement.
   • While inches are used in the United States, you will often need to convert this unit of measurement to one belonging to the metric system (like millimeters) for scientific purposes.
   • Conversely, there are 0.0393700787402 inches in one millimeter.^[3]
2. 2

   Write down the inches measurement. To convert a measurement taken in inches, you need to begin the problem by writing down the original measurement.

   • This measurement will then be converted into millimeters by comparing it to the relationship between inches and millimeters.
   • Example: 7 inches

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3. 3

   Multiply this measurement by 25.4. You need to multiply the current inches measurement by the ratio of millimeters to inches, or 25.4 mm / 1 in.

   • The inches value in this ratio needs to be placed in the denominator since it will have to cancel out the inches value in your original measurement. Once all the inches are canceled out, the millimeters will be the only remaining unit of measurement.
   • Example: 7 in * (25.4 mm / 1 in) = 177.8 mm * (in/in) = 177.8 mm
4. 4

   Write down the final answer. If you did the problem correctly, the answer you come up with should be your final answer in millimeters.

   • Example: 177.8 mm
   See Also

   Convert inches to mmInches to Millimeter Conversion (in to mm)Convert Inch to Millimeter (in to mm) | Length Units Converter | Internet Tools WizardInch to Millimeter Converter :: Ace Online Tools

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1. 1

   Check a ruler. One ruler is 12 inches long or 1 foot. Many rulers list the inches on one side but also list centimeters and millimeters on the other side. If your original measurement is 12 inches or below, you can use one of these rulers to measure the same distance in millimeters.

   • Note that the millimeter marks on a ruler are all the small dashes in between the larger centimeter measurements. There should be 10 mm per 1 cm.
2. 2

   Use a website to automatically convert the measurement. If you need to quickly find out the millimeter equivalent to a measurement in inches, you can do so by using an automatic conversions website.

   • Go to the website and locate the conversion boxes.
   • Type the numbers into their respective boxes and select the units you are trying to convert, if necessary.
   • Hit the “Calculate” button or other corresponding button to be shown the answer.
   • Websites that will calculate this conversion for you include:
     • MetricConversions.Org (http://www.metric-conversions.org/length/inches-to-millimeters.htm)
     • CheckYourMath.Com (http://www.checkyourmath.com/convert/length/inches_mm.php)
     • Additionally, you can type the problem (i.e., 7 in = mm) directly into most major search engines, including Google and Bing, and the search engine should be able to convert the problem and return the answer to you on the results page.
3. 3

   Look at a common conversions chart. For smaller amounts of inches, you might be able to locate the measurement on a conversion chart, such as the one below. Locate the number of inches and look beside it to view the number of millimeters equal to the inches value.

   • 1/64 in = 0.3969 mm
   • 1/32 in = 0.7938 mm
   • 1/16 in = 1.5875 mm
   • 1/8 in = 3.1750 mm
   • 1/4 in = 6.3500 mm
   • 1/2 in = 12.7000 mm
   • 3/4 in = 19.0500 mm
   • 7/8 in = 22.2250 mm
   • 15/16 in = 23.8125 mm
   • 31/32 in = 24.6062 mm
   • 63/64 in = 25.0031 mm
   • 1 in = 25.4001 mm
   • 1 1/8 in = 28.5750 mm
   • 1 1/4 in = 31.7500 mm
   • 1 3/8 in = 34.9250 mm
   • 1 1/2 in = 38.1000 mm
   • 1 5/8 in = 41.2750 mm
   • 1 3/4 in = 44.4500 mm
   • 2 in = 50.8000 mm
   • 2 1/4 in = 57.1500 mm
   • 2 1/2 in = 63.5000 mm
   • 2 3/4 in = 69.8500 mm
   • 3 in = 76.2000 mm
   • 3 1/4 in = 82.5500 mm
   • 3 1/2 in = 88.9000 mm
   • 3 3/4 in = 95.2500 mm
   • 4 in = 101.6000 mm
   • 4 1/2 in = 114.3000 mm
   • 5 = 127.0000 mm
   • 5 1/2 in = 139.7000 mm
   • 6 in = 152.4000 mm
   • 8 in = 203.2000 mm
   • 10 in = 254.0000 mm

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1. 1

   Convert inches to centimeters. There are 2.54 cm in 1 inch, so in order to convert inches to centimeters, you need to multiply the original inches measurement by a value of 2.54 centimeters.^[4]

   • Example: 7 in * (2.54 cm / 1 in) = 17.78 cm
   • Note that the number of centimeters will be one decimal place larger than the number of millimeters. If you have the number of millimeters, you can also find the number of centimeters by shifting the decimal place one numeral over to the left.
2. 2

   Convert inches to meters. There are 0.0254 m in 1 inch, so in order to convert inches to meters, you need to multiply the original inches measurement by a value of 0.0254 m.

   • Example: 7 in * (0.0254 m / 1 in) = 0.1778 m
   • Note that the number of meters will be three decimal places larger than the number of millimeters. If you have the number of millimeters, you can also find the number of meters by shifting the decimals place three numerals over to the left.
3. 3

   Convert millimeters to inches. If you want to calculate the number of inches when you have the number of millimeters, you can do so by either multiplying the number of millimeters by 0.0393700787 inches or by dividing the number of millimeters by 25.4 millimeters.

   • Example: 177.8 mm * (0.0393700787 in / 1 mm) = 7 in
   • Example: 177.8 mm * (1 in / 25.4 mm) = 7 in

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1. 1

   Answer the question: how many millimeters is 4.78 inches? To find the answer, you will need to multiply 4.78 inches by 25.4 millimeters.

   • 4.78 in * (25.4 mm / 1 in) = 121.412 mm
2. 2

   Convert 117 inches into millimeters. Do so by multiplying 117 inches by 25.4 millimeters.

   • 177 in * (25.4 mm / 1 in) = 4495.8 mm
3. 3

   Determine how many millimeters are in 93.6 inches. This answer can be found by multiplying 93.6 inches and 25.4 millimeters.

   • 93.6 in * (25.4 mm / 1 in) = 2377.44 mm
4. 4

   Figure out how to convert 15.101 inches into millimeters. Find the answer by multiplying 15.101 inches and 25.4 millimeters.

   • 15.101 * (25.4 mm / 1 in) = 383.5654 mm

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