In this guide, we will explain everything about millimeters to inches conversion. Below, I have added a millimetre to inches calculator. You can use it for quick and easy measurement.
But if you want to check common calculations without any complex math, you can see following mm to inches conversion table. After that, we will also discuss imperial and metric unit system comparison plus formulas to interconvert inches and millimeters.
| From: | millimeter | |
| To: | inch |
Millimeter To Inches Conversion Table
This information is helpful for you to quickly find the inch value of a millimeter measurement. We also mentioned fractional and decimal inch values so you can see the correct conversion without doing math yourself.
| Millimeters | Decimal inches | Fractional Inches | Millimeters | Decimal inches | Fractional Inches |
| 1 mm | 0.03937″ | 1/25″ | 300 mm | 11.8110″ | 11 13/16″ |
| 2 mm | 0.07874″ | 5/64″ | 350 mm | 13.7795″ | 13 25/32″ |
| 3 mm | 0.11811″ | 1/8″ | 400 mm | 15.7480″ | 15 3/4″ |
| 4 mm | 0.15748″ | 5/32″ | 450 mm | 17.7165″ | 17 23/32″ |
| 5 mm | 0.19685″ | 3/16″ | 500 mm | 19.6850″ | 19 11/16″ |
| 6 mm | 0.23622″ | 1/4″ | 600 mm | 23.6220″ | 23 5/8″ |
| 7 mm | 0.27559″ | 9/32″ | 700 mm | 27.5591″ | 27 9/16″ |
| 8 mm | 0.31496″ | 5/16″ | 800 mm | 31.4961″ | 31 1/2″ |
| 9 mm | 0.35433″ | 11/32″ | 900 mm | 35.4331″ | 35 7/16″ |
| 10 mm | 0.39370″ | 3/8″ | 1000 mm | 39.3701″ | 39 3/8″ |
| 15 mm | 0.59055″ | 19/32″ | 1100 mm | 43.3071″ | 43 5/16″ |
| 20 mm | 0.78740″ | 25/32″ | 1200 mm | 47.2441″ | 47 1/4″ |
| 25 mm | 0.98425″ | 1″ | 1300 mm | 51.1811″ | 51 3/16″ |
| 30 mm | 1.18110″ | 1 3/16″ | 1400 mm | 55.1181″ | 55 1/8″ |
| 35 mm | 1.37795″ | 1 3/8″ | 1500 mm | 59.0551″ | 59 1/16″ |
| 40 mm | 1.57480″ | 1 9/16″ | 1600 mm | 62.9921″ | 62 63/64″ |
| 45 mm | 1.77165″ | 1 3/4″ | 1700 mm | 66.9291″ | 66 15/16″ |
| 50 mm | 1.96850″ | 1 31/32″ | 1800 mm | 70.8661″ | 70 7/8″ |
| 60 mm | 2.36220″ | 2 3/8″ | 1900 mm | 74.8031″ | 74 51/64″ |
| 70 mm | 2.75591″ | 2 3/4″ | 2000 mm | 78.7402″ | 78 47/64″ |
| 80 mm | 3.14961″ | 3 1/8″ | 2100 mm | 82.6772″ | 82 43/64″ |
| 90 mm | 3.54331″ | 3 9/32″ | 2200 mm | 86.6142″ | 86 5/8″ |
| 100 mm | 3.93701″ | 3 15/16″ | 2300 mm | 90.5512″ | 90 35/64″ |
| 150 mm | 5.90551″ | 5 29/32″ | 2400 mm | 94.4882″ | 94 31/64″ |
| 200 mm | 7.87402″ | 7 7/8″ | 2500 mm | 98.4252″ | 98 27/64″ |
| 250 mm | 9.84252″ | 9 27/32″ | 3000 mm | 118.1102″ | 118 7/64″ |
Mathematical Definition of MM and Inch
What is mm? MM stands for millimeter. A millimeter is a unit of measurement in a metric system used to measure length or distance. The prefix “milli” means one thousandth, so 1 millimeter equals one thousandth of a meter (0.001 m). It is part of the International System of Units (SI) as well. Also note that, “millimetre” is the British/international spelling and “millimeter” is the American spelling.
What is an inch? An inch (in) is a unit of length used mainly in the United States Customary and British Imperial measurement systems. The common symbols for inch are in and symbol: ″. One inch equals 25.4 millimeters. Further, one inch equals one-twelfth of a foot, so 12 inches make 1 foot.
How To Convert Millimeters To Inches?
You can easily convert millimetres to inches with a simple formula. There are 25.4 mm in one inch. You only need to divide the millimetre value by 25.4.
Millimeters to inches conversion formula: Inches = Millimetres ÷ 25.4
Now you can follow this method.
- Step 1: Take the measurement in millimetres.
- Step 2: Divide the value by 25.4.
- Step 3: The answer gives you the value in inches.
For example: Let’s convert 100 mm to inches. The millimetre value you want to convert is 100. According to the formula, you should divide 100 by 25.4. Enter 100 ÷ 25.4 on your calculator and press the equals (=) sign. You will get 3.937 inches as a result.
How To Convert Inches To MM?
To convert inches into millimetres, you need to multiply the inch value by 25.4. One millimetre contains 0.03937 inches.
Inches to mm conversion formula: Millimetres = Inches × 25.4
Follow these simple steps.
Step 1: Take the measurement in inches.
Step 2: Multiply the value by 25.4.
Step 3: The result will give you the number in millimetres.
For example: Suppose you want to convert 5 inches into millimetres. You can start with the value 5 and multiply it by 25.4 using the conversion formula. On your calculator, you enter 5 × 25.4 and press the equals (=) sign. The result will be 127 mm.
Metric System vs Imperial System of Units
The metric system and imperial system use different units to describe length, weight and other measurements. You will generally notice them if you are reading product sizes, technical data or measurements. In this section, you will see the actual difference between both system of units.
Metric System of Units
The metric system is an international measurement system that uses units based on powers of 10. Basically, it follows a simple base 10 structure, so you can convert between units (e.g millimetres, centimetres & metres) by moving the decimal point. For example, 1 metre contains 1000 millimetres. Today, it is commonly called SI which stands for International System of Units.
For measurement, this system uses units such as millimetres (mm), centimetres (cm), metres (m) and kilometres (km). France developed the modern metric system during the 1790s and its government officially adopted it in 1795. It is the official measurement system in almost all countries and some of them we listed below.
- Australia
- Japan
- Mexico
- South Africa
- Canada
- France
- India
- Italy
- Spain
- United Kingdom
You will commonly notice the use of metric units in industries such as automotive manufacturing, engineering, aviation and aerospace, science, healthcare and international trade.
Imperial Unit System
The Imperial system is a measurement system that includes units such as the inch for length, mile for distance and pound for weight. The British government introduced the Imperial system in 1824 through the British Weights and Measures Act.
Then it became the standard system for measurement across the British Empire. The United States Customary System (USCS) is also developed from the British Imperial System. Only three countries are commonly listed as using an Imperial-based measurement system. These include:
- United States of America
- Liberia
- Myanmar
The industries that use the imperial system of units are construction, carpentry, real estate, aviation, shipping, automotive & mechanical manufacturing, food and beverage.
Silicone and Rubber Hose Diameter Conversion
If you are a retailer, manufacturer or engineer who purchases hose products, you mostly deal with millimeters and inches calculations. Because suppliers from different countries use their own measurement systems.
Therefore, it can be hard for you to compare sizes when you choose a hose, fitting or replacement. We prepared this table to show you common silicone and rubber hose diameters in mm and inches for quick comparison.
| Inner Diameter (mm) | Inches | Application |
| 2 mm | 5/64 inches | Automotive vacuum lines & lab fluid transfer |
| 6 mm | 1/4 inches | Fuel spill-off/return lines, small engine fuel tubing or boost gauge lines |
| 8 mm | 5/16 in | Engine vacuum system, low-pressure fuel supply & air bleed hoses |
| 10 mm | 3/8 in | Transmission cooler lines, auxiliary coolant overflow or air intake vacuum |
| 13 mm | 1/2 inches | Vehicle heater matrix lines, coolant bypass & industrial fluid transfer |
| 16 mm | 5/8 in | Automotive heater hoses and heavy-duty fluid transfer |
| 20 mm | 25/32 inches | Commercial heater hose, marine coolant lines and water pump bypass |
| 25 mm | 1 in | Silicone radiator hose and industrial water delivery |
| 32 mm | 1-1/4 in | Engine coolant hoses and industrial suction/discharge |
| 38 mm | 1-1/2 inches | Standard automotive radiator inlet/outlet hoses and turbo intercooler intake piping |
| 50 mm | 1.968 inch | Main radiator coolant tubes and heavy equipment cooling systems |
How Dash Size is Related to MM and Inches?
Tubes or hoses are used to carry air, water, coolant or other fluids in automotive and industrial systems. These tubes have different inside diameters, so manufacturers use several ways to show their sizes.
Mostly, you will see their dimension listed in millimetres, inches or dash sizes. A dash size gives you an approximate idea of a hose or tube’s inside diameter. It uses a number to represent the nominal size in inches. But it does not show the exact measured inside diameter.
| Dash Size | Nominal Hose ID (mm) | Nominal Hose ID (inches) |
| -2 | 3.2 mm | 1/8″ |
| -3 | 4.8 mm | 3/16″ |
| -4 | 6.4 mm | 1/4″ |
| -5 | 7.9 mm | 5/16″ |
| -6 | 9.5 mm | 3/8″ |
| -8 | 12.7 mm | 1/2″ |
| -10 | 15.9 mm | 5/8″ |
| -12 | 19.1 mm | 3/4″ |
| -16 | 25.4 mm | 1″ |
| -20 | 31.8 mm | 1-1/4″ |
Conclusion
So, you can use mm to inches conversion in your business as well as in your daily life. For example, you need it when you buy products online, check product dimensions, measure furniture or compare tool sizes.
If you need custom automotive/industrial hoses and tubes according to your required size or application, RONTEIX is here to help you. Send us a message and get an affordable quote.
FAQs
What does 10 mm look like?
The measurement of 10 mm equals exactly 1 centimeter. Without a ruler, you can imagine 10 mm as roughly the width of pinky fingernail, the diameter of a AAA battery, the height of a LEGO brick or the thickness of a stack of around 10 credit cards.
What is the metric equivalent of 3/8 inch?
3/8 inch is equal to 9.525 mm, which is rounded to 9.5 mm. This means 3/8 inch is slightly smaller than 10 mm with a difference of about 0.5 mm.
Is 6.5 millimeters the same as 1/4″?
No, 6.5 mm is not exactly the same as 1/4 inch but they are very close. 1/4 inch equals 6.35 mm, so 6.5 mm is only slightly larger than 1/4 inch.
12 mm to inches fraction?
12 mm is equal to 0.47 inches. As a common inch fraction, 12 mm is closest to 15/32 inch. It is equal to 11.906 mm. This makes 15/32 inch a close practical match for 12 mm.
How to tell if hose is 3/4 or 5/8?
To check if a hose is 3/4 inch or 5/8 inch, you should measure its inside diameter (ID), not the outside diameter. A 5/8-inch hose has an ID of around 15.9 mm and a 3/4-inch hose has an ID of 19.1 mm.
Can 3/4 and 5/8 hoses fit together?
Yes, you can connect 3/4-inch and 5/8-inch garden hoses together if both have standard 3/4-inch GHT fittings. However, if you want to join two bare hose ends, you need a 5/8-inch × 3/4-inch hose adapter or mender. Although the hose sizes differ, their standard fittings can use the same thread size.
Which is bigger, 1/2 or 3/4 hose?
A 3/4-inch hose is bigger compared to a 1/2-inch hose. The size generally refers to the hose’s inside diameter. Hence, a 3/4-inch hose has a larger opening and can carry more water than a 1/2-inch hose.
Is hose diameter ID or OD?
Hose diameter is always measured by its ID (inside diameter). If you see a hose size such as 1/2 inch or 3/4 inch, it refers to the ID of the hose. The outside diameter (OD) measures the full width of the hose from one outer edge to the other.
What is dash size in thread?
A dash size in a thread is a standard number used to identify the nominal size of a threaded hose or tube. It basically represents the size in 1/16-inch increments such as -8 = 8/16 inch = 1/2 inch.
Where can I use both mm and inches calculations?
You can use both millimeters (metric) and inches (imperial) in engineering, manufacturing, automotive repair, construction and plumbing. When you use both units in the same work, it is called dual dimensioning.
