Mil to Millimeter (mm) Conversion Calculator

Convert mils (thousandths of an inch) to millimeters and vice versa. Essential for PCB, engineering, and manufacturing.

Quickly convert between mils (thou) and millimeters (mm) for PCB design, technical drawings, and precision engineering. Supports both mil→mm and mm→mil conversions, with multi-value input and real-world examples.

Examples

Click an example to load it into the calculator.

PCB Trace Width

pcb

Convert a standard PCB trace width from mils to millimeters.

Input: 10

Direction: Mil → Millimeter (mm)

Engineering Drawing

engineering

Convert a technical drawing dimension from millimeters to mils.

Input: 2.54

Direction: Millimeter (mm) → Mil

Multiple Values

multi

Convert several mil values to millimeters at once.

Input: 50, 100, 250

Direction: Mil → Millimeter (mm)

General Use

general

Convert a millimeter measurement to mils for manufacturing.

Input: 1

Direction: Millimeter (mm) → Mil

Other Titles
Understanding Mil to Millimeter (mm) Conversion: A Comprehensive Guide
Master precision unit conversion for PCB, engineering, and manufacturing. Learn formulas, best practices, and real-world applications for mil and millimeter conversions.

What is Mil to Millimeter Conversion?

  • Definition of Mil and Millimeter
  • Why Convert Between Mil and mm?
  • Where is This Conversion Used?
A 'mil' (also known as a 'thou') is a unit of length equal to one thousandth of an inch (0.001 inch). The millimeter (mm) is a metric unit of length equal to one thousandth of a meter. Converting between mils and millimeters is essential in fields where both imperial and metric measurements are used, such as PCB design, engineering, and manufacturing.
Why is This Conversion Important?
Many technical drawings, PCB layouts, and manufacturing specifications use mils for fine measurements, especially in the United States. However, most of the world uses millimeters. Accurate conversion ensures compatibility, precision, and quality in engineering and production.
Common Use Cases
  • PCB trace width and spacing
  • Technical drawing dimensions
  • Manufacturing tolerances
  • Electronics assembly
  • Quality control and inspection

Typical Conversion Scenarios:

  • Converting a 10 mil PCB trace to mm for international manufacturing
  • Translating a 2.54 mm pin spacing to mils for US-based PCB design
  • Batch converting multiple mil values to mm for a technical drawing

Step-by-Step Guide to Using the Mil to mm Converter

  • Inputting Values
  • Selecting Conversion Direction
  • Interpreting Results
To use the Mil to mm Converter, simply enter the value(s) you wish to convert. You can input a single value or multiple values separated by commas or spaces. Next, select the conversion direction: Mil to mm or mm to Mil. Click 'Convert' to see the results instantly.
Input Tips
  • Use only positive numbers
  • Separate multiple values with commas or spaces
  • Double-check units before converting
Result Interpretation
The results will display your input values, the conversion direction, and the converted values with appropriate units. You can copy the results for use in your projects or documentation.

How to Use the Calculator:

  • Convert 100 mil to mm: Enter '100', select 'Mil to mm', click Convert
  • Convert 2.54 mm to mil: Enter '2.54', select 'mm to Mil', click Convert
  • Convert 50, 100, 250 mil to mm: Enter '50, 100, 250', select 'Mil to mm', click Convert

Real-World Applications of Mil and mm Conversion

  • PCB Design and Manufacturing
  • Engineering and Technical Drawings
  • Quality Control and Inspection
Mil to mm conversion is crucial in PCB design, where trace widths, pad sizes, and component spacing are often specified in mils. International manufacturers may require these values in millimeters. Similarly, engineering drawings may use both units, requiring accurate conversion for production and inspection.
Electronics and PCB Industry
  • PCB trace width: 10 mil = 0.254 mm
  • Pin spacing: 100 mil = 2.54 mm
  • SMD pad size: 20 mil = 0.508 mm
Engineering and Manufacturing
  • Technical drawing dimensions
  • Tolerance specifications
  • Quality control measurements

Industry Examples:

  • A PCB designer converts 10 mil trace width to mm for a European manufacturer
  • An engineer converts 2.54 mm to mil for a US-based technical drawing
  • A quality inspector batch converts mil values to mm for inspection reports

Common Misconceptions and Correct Methods

  • Mil vs. Millimeter Confusion
  • Precision and Rounding
  • Batch Conversion Best Practices
A common misconception is that 'mil' and 'millimeter' are similar due to their names. In reality, 1 mil = 0.0254 mm, which is much smaller than 1 mm. Always check the unit before converting.
Precision Matters
For engineering and PCB work, precision is critical. Always use at least four decimal places for conversions. Avoid rounding until the final result.
Batch Conversion Tips
When converting multiple values, ensure all are in the same unit and format. Use the calculator's multi-value input for efficiency and accuracy.

Best Practice Reminders:

  • Never confuse mil (0.001 inch) with mm (1 millimeter)
  • Use four decimal places for all conversions
  • Double-check input units before batch conversion

Mathematical Derivation and Examples

  • Conversion Formulas
  • Worked Examples
  • Advanced Usage
The conversion formulas are simple but must be applied precisely. To convert mil to mm: mm = mil × 0.0254. To convert mm to mil: mil = mm ÷ 0.0254. Always use the exact factor for accuracy.
Worked Examples
  • 100 mil × 0.0254 = 2.54 mm
  • 2.54 mm ÷ 0.0254 = 100 mil
  • 50 mil × 0.0254 = 1.27 mm
Advanced Usage
For advanced users, the calculator supports batch conversion and copying results for use in CAD, PCB, or documentation workflows.

Formula Examples:

  • Convert 100 mil to mm: 100 × 0.0254 = 2.54 mm
  • Convert 2.54 mm to mil: 2.54 ÷ 0.0254 = 100 mil
  • Convert 50, 100, 250 mil to mm: 1.27, 2.54, 6.35 mm