PCB Copper Weight to Thickness — Table & Calculator
Convert copper weight (oz/ft²) to thickness in µm and mil, get sheet resistance, and estimate a trace's DC resistance.
Copper weight reference
Thickness and sheet resistance are computed for pure copper at 20 °C — 1 oz/ft² spreads to 34.8 µm.
| Weight | Thickness (µm) | Thickness (mil) | Sheet resistance (mΩ/□) | Typical use |
|---|---|---|---|---|
| 0.5 oz | 17.4 | 0.69 | 0.991 | Inner layers, fine-pitch HDI |
| 1 oz | 34.8 | 1.37 | 0.495 | The default for outer layers |
| 2 oz | 69.6 | 2.74 | 0.248 | Power sections, motor drivers |
| 3 oz | 104.4 | 4.11 | 0.165 | Heavy current, thick-copper fabs |
| 4 oz | 139.2 | 5.48 | 0.124 | Heavy copper (specialist fabs) |
| 5 oz | 174.0 | 6.85 | 0.099 | Heavy copper (specialist fabs) |
| 6 oz | 208.8 | 8.22 | 0.083 | Heavy copper (specialist fabs) |
What copper weight means
PCB copper is specified by weight: the ounces of copper rolled onto one square foot. One ounce works out to a 34.8 µm (1.38 mil)layer, and everything scales linearly from there.
R = R_sheet × (length ÷ width)
Sheet resistance makes trace resistance easy to reason about: every "square" of trace — any stretch as long as it is wide — has the same resistance regardless of its size. A 1 oz trace 50 squares long is 50 × 0.495 ≈ 25 mΩ.
Related
Size a trace for current with thePCB trace current calculator, check vias with thevia properties calculator, or estimate wire runs with thewire voltage drop calculator.
Outer layers are usually thicker than ordered
The conversion here is exact arithmetic, but the copper on a finished board often is not what was specified. Outer layers receive additional plating during via formation, so a board ordered as 1 oz outer commonly arrives closer to 1.5 oz. Inner layers get exactly what was ordered, since nothing is plated onto them. If a calculation is close enough to the limit for that difference to matter — atrace current or an impedance target — ask the fabricator what their finished thickness actually is.