Understanding the conversion between millimeters (mm) and thousandths of an inch (mils or thou) is crucial for professionals in engineering, manufacturing, and construction. The metric system is widely used around the world, while the imperial system remains common in North America and some industries.
A millimeter (mm) is a metric unit, whereas a thousandth of an inch (mil or thou) is an imperial unit. Converting between them allows for accurate measurements in different systems. This guide will explain the conversion process, applications, and importance of precision in various fields.
What Is a Thousandth of an Inch?
Definition of Thousandth of an Inch
A thousandth of an inch, also called a mil or thou, is equal to 0.001 inches. It is commonly used in engineering, electronics, metalworking, and coatings.
Thousandth of an Inch vs. Millimeter
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1 mm = 39.37 mils (thousandths of an inch)
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1 mil = 0.0254 mm
For example, 5 mm = 196.85 mils, which is useful for industries that require precise material thickness.
How to Convert MM to Thousandths of an Inch
Basic Conversion Formula
To convert millimeters to thousandths of an inch, use this formula:
Conversion Table (MM to Mils)
| Millimeters (mm) | Thousandths of an Inch (mils) |
|---|---|
| 0.1 mm | 3.94 mils |
| 0.5 mm | 19.69 mils |
| 1 mm | 39.37 mils |
| 2 mm | 78.74 mils |
| 5 mm | 196.85 mils |
| 10 mm | 393.70 mils |
This table helps visualize common conversions.
Applications of MM to Thousandth of an Inch Conversion
1. Plastic Film and Sheet Thickness
Many industries measure plastic film and sheets in mils.
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Garbage bags are often 0.5 to 2 mils thick.
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Plastic tarps range from 3 to 10 mils.
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Food packaging films require precision in microns or mils.
2. Metalworking and Sheet Metal Thickness
Metal thickness is often specified in mils, especially in aluminum, copper, and steel sheets.
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Aluminum foil is about 0.63 mils thick.
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Standard automotive steel panels are 20 to 50 mils thick.
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Coatings on galvanized steel range from 1 to 5 mils.
3. Electronics and PCB Manufacturing
In the electronics industry, wire thickness and PCB components are measured in mils.
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Printed circuit board (PCB) traces are typically 1 to 2 mils wide.
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Wire insulation uses mils to ensure proper safety and durability.
4. Medical and Scientific Equipment
Precision instruments in medical and laboratory settings often use both mm and mils.
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Medical tubing thickness is measured in mils for consistency.
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Microsurgical tools require precise mm-to-mils conversions.
5. Coatings and Paint Applications
Paint and protective coatings are commonly measured in mils.
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Automotive clear coats range from 2 to 5 mils.
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Industrial epoxy coatings can be 10 to 20 mils thick.
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Powder coatings for metals require exact mil measurements.
Why Precise Conversion Matters
1. Avoiding Measurement Errors
Small miscalculations in mm to mil conversions can lead to:
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Incorrect material selection.
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Improper thickness for coatings.
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Incompatibility with manufacturing standards.
2. Industry Standardization
Many industries use both metric and imperial systems, making accurate conversion essential. For example:
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European manufacturers use millimeters.
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U.S. manufacturers often use thousandths of an inch.
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Global suppliers must ensure accurate conversion.
3. Ensuring Product Quality
Precise thickness measurements affect durability, performance, and compliance with regulations.
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Electronics require exact PCB trace widths.
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Medical devices must meet strict dimensional standards.
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Paint coatings must provide uniform protection.
Comparing MM, Mils, and Other Units
1. MM vs. Mil vs. Microns
Microns (µm) are also used for fine measurements.
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1 mm = 1000 microns = 39.37 mils.
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1 mil = 25.4 microns.
2. MM vs. Inches in Industrial Use
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1 mm = 0.03937 inches.
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1 inch = 25.4 mm.
Industries like aerospace, automotive, and medical devices require accurate conversions.
3. MM vs. Gauge for Wire and Metal Thickness
Gauge systems differ from mils and mm.
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Wire gauge uses a non-linear scale.
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Plastic gauge uses mils (1 mil = 100 gauge for thin films).
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Sheet metal gauge differs for steel and aluminum.
How to Easily Convert MM to Mils
1. Online Conversion Tools
Many engineering and industrial websites provide mm-to-mil calculators.
2. Manual Calculation
Using the formula:
For example, 2 mm would be:
3. Reference Charts
Keeping a conversion chart handy helps professionals quickly switch between mm, mils, and microns.
Converting millimeters to thousandths of an inch (mils) is essential for many industries, including manufacturing, engineering, electronics, coatings, and medical devices. Since 1 mm equals 39.37 mils, understanding this relationship ensures accuracy in product specifications, quality control, and industry compliance.
Whether working with plastic films, metal sheets, electrical components, or protective coatings, accurate mm-to-mil conversions are key to achieving the desired thickness and performance in materials. Using conversion tools, reference tables, and precise calculations helps professionals ensure seamless measurements across metric and imperial systems.