Free Tool

PCB Unit Converter

Instantly convert between common PCB measurement units. Essential for working with international datasheets and specifications.

Length Conversion

Convert between mil, mm, inch, and micron

0.0254

Copper Weight

Convert between oz/ft² and thickness

35.0018

Area Conversion

Convert between square units

0.00064516

Temperature

Convert between Celsius and Fahrenheit

77
Fahrenheit (°F)

Quick Reference

Copper Weight to Thickness

oz/ft²MicronMil
1/3 oz9 μm0.35 mil
1/2 oz17 μm0.7 mil
1 oz35 μm1.4 mil
2 oz70 μm2.8 mil
3 oz105 μm4.2 mil

Common Conversions

1 mil0.0254 mm = 25.4 μm
1 mm39.37 mil
1 inch25.4 mm = 1000 mil
1 oz copper35 μm = 1.4 mil thickness

Unit Tips

  • Mil (thousandths of an inch) is commonly used in US PCB specifications
  • Metric (mm) is standard in most international specifications
  • Copper weight in oz/ft² is an industry-standard way to specify copper thickness
  • 1 oz copper ≈ 35 μm thickness is a fundamental PCB conversion
  • When in doubt, check your manufacturer's preferred unit system

Frequently Asked Questions

What is a mil in PCB design?
A mil is 1/1000 of an inch (0.001 inch or 0.0254 mm). It's commonly used in the US PCB industry for trace widths, spacing, and hole sizes. For example, a '6 mil trace' means a trace that is 0.006 inches or about 0.15 mm wide.
How do I convert oz copper to thickness?
Copper weight in oz/ft² converts to thickness: 1 oz = 35 μm (1.4 mil), 2 oz = 70 μm (2.8 mil), 0.5 oz = 17 μm (0.7 mil). This is based on the weight of copper per square foot of the PCB surface.
Should I use mil or mm for my design?
It depends on your manufacturer and design tools. US manufacturers often prefer mil, while Asian and European manufacturers may prefer mm. Most modern CAD tools support both. The key is consistency - pick one system and stick with it throughout your design.
What is the standard copper weight for flex PCB?
Standard copper weights for flex PCB are 1/2 oz (17 μm) and 1 oz (35 μm). Thinner copper (1/3 oz) is used for tighter bends, while thicker copper (2 oz) is used for high-current applications. Thinner copper allows for smaller bend radii.

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Definition And Context

Unit conversion is the process of expressing the same physical quantity in different measurement systems without changing its underlying value. In PCB work that commonly includes length, copper weight, area, and temperature, each of which appears in design files, fabrication notes, and supplier communication.

This page was reviewed for GEO clarity by Hommer Zhao of WIRINGO so the content explains the underlying engineering terms, not only the interface or headline claim.

Why Unit Errors Still Cause Real Problems

Most conversion mistakes do not come from a lack of math. They come from switching contexts too quickly. A layout engineer may think in mil, a mechanical drawing may be in millimeters, and a supplier may describe copper weight in ounces. If the project does not normalize those terms early, avoidable confusion reaches the quote, the drawing, and sometimes the released part.

Simple reference tools help because they take one repeated source of friction out of the workflow. That matters most when multiple suppliers or regions are involved and every conversation depends on the same thickness, spacing, or area number being understood the same way.

Where Conversion Discipline Matters Most

Conversion discipline matters in tolerance-sensitive communication. Minimum trace width, finished copper thickness, board outline, and thermal limits are all values that should be stated unambiguously. A drawing that mixes conventions without a clear primary unit increases review time and creates more chances for manual interpretation.

The practical rule is to choose one release convention, then cross-check any imported values. That is particularly important when legacy data or customer notes are copied into a new project package.

Common Conversion Risk Points

Value TypeCommon Mixed UnitsWhy A Check Helps
Trace geometrymil and mmPrevents width and spacing mistakes
Copper thicknessoz and micronSupports consistent fabrication notes
Areasq mm and sq inImproves panel and quoting discussions
TemperatureC and FAvoids process or storage confusion
Mechanical dimensionsinch and mmKeeps enclosure and connector fit aligned

Authoritative References

The external references below are included as basic background reading for common manufacturing and interconnect terms used on this page.

  • IPC

    https://en.wikipedia.org/wiki/IPC_(electronics)

  • ISO 9001

    https://en.wikipedia.org/wiki/ISO_9001

  • Crimp joining

    https://en.wikipedia.org/wiki/Crimp_(joining)