Convert between copper weight (oz/ft²) and thickness in mils, micrometers, and millimeters. Essential for PCB stackup design, trace width calculations, and impedance modeling.
Conversion factor: 1 oz/ft² = 1.4 mil = 35.56 µm = 0.03556 mm
| Copper Weight (oz/ft²) | Thickness (mil) | Thickness (µm) | Thickness (mm) | Typical Use |
|---|---|---|---|---|
| 0.5 oz | 0.7 | 17.5 | 0.0175 | Fine-pitch HDI inner layers |
| 1 oz | 1.4 | 35 | 0.035 | Standard PCB (most common) |
| 2 oz | 2.8 | 70 | 0.070 | Power electronics, LED boards |
| 3 oz | 4.2 | 105 | 0.105 | High-current industrial |
| 4 oz | 5.6 | 140 | 0.140 | Automotive, heavy copper |
| 6 oz | 8.4 | 210 | 0.210 | Bus bars, extreme current |
Copper weight is expressed in ounces per square foot (oz/ft²). One ounce of copper spread uniformly over one square foot produces a foil 1.4 mils (35 µm) thick. This convention dates back to the early days of PCB manufacturing and remains the industry standard.
Copper thickness directly affects trace current capacity, impedance, and thermal performance. Thicker copper carries more current at the same trace width but costs more and limits minimum trace/space for etching. Most standard PCBs use 1 oz copper; power boards use 2–4 oz.
Copper foil is a conductive metal layer laminated into the PCB stackup, and copper weight refers to the historical mass-based shorthand used to describe its approximate thickness. That definition is important because current carrying capacity, thermal spread, and manufacturable etch geometry all depend on the resulting thickness, not just the label itself.
Copper weight is a manufacturing shorthand for foil thickness based on how much copper mass is spread over one square foot. It is widely used even when engineers ultimately care about the resulting thickness.
Copper thickness affects current capacity, voltage drop, thermal behavior, etching limits, and impedance assumptions. It is one of the variables that links layout geometry to real electrical and manufacturing performance.
It is commonly treated as about 35 um for engineering discussion, but finished copper can vary with process details, plating, and where in the stackup the copper is measured.
Heavier copper is common in power conversion, automotive, LED lighting, and industrial control boards where traces must carry more current or spread heat more effectively.
Use the convention your fabricator expects, but make sure the drawing, quote, and stackup all refer to the same finished copper intent so no one has to infer it later.