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PCB copper thickness is traditionally specified as a weight, not a length — a holdover from the manufacturing process, where a sheet of copper foil of a given thickness weighs a specific amount per square foot when rolled to that thickness. "1 oz copper" means the foil weighs 1 ounce per square foot, which corresponds to a physical thickness of about 1.378 mils (35 µm). Despite the unusual unit, once you know the conversion it behaves exactly like any other thickness specification.
| Copper weight | Thickness (µm) | Thickness (mils) | Typical use |
|---|---|---|---|
| 0.5 oz | 17.5 µm | 0.689 mils | Fine-pitch, high-density inner layers |
| 1 oz | 35.0 µm | 1.378 mils | Standard for most consumer/general PCBs |
| 2 oz | 70.0 µm | 2.756 mils | Power electronics, motor drivers |
| 3 oz | 105.0 µm | 4.134 mils | High-current busbar-style traces |
| 4 oz+ | 140.0 µm+ | 5.512 mils+ | Very high-current / heavy-copper boards |
Copper weight directly affects two of the most important PCB electrical properties covered elsewhere in this section: current-carrying capacity (a thicker trace of the same width can carry more current before overheating — see the Trace Width calculator) and resistance (a thicker trace has less resistance and less voltage drop for the same width and length — see the Trace Resistance calculator). Choosing a heavier copper weight is often the simplest way to fit more current into limited board space, at the cost of a modest manufacturing price increase and potentially wider minimum trace spacing (heavier copper is harder to etch precisely).
It is the traditional way of specifying copper foil thickness on a PCB, expressed as the weight (in ounces) of copper per square foot when rolled to that thickness. "1 oz copper" is a specific, standard thickness of about 35 µm (1.378 mils).
Multiply ounces by 34.79 to get micrometres: 1 oz ≈ 34.79 µm (commonly rounded to 35 µm), 2 oz ≈ 69.6 µm, and so on.
Multiply ounces by 1.378 to get mils (thousandths of an inch): 1 oz ≈ 1.378 mils, 2 oz ≈ 2.756 mils.
1 oz is the most common default for general-purpose and consumer electronics PCBs. Power electronics and high-current boards commonly step up to 2 oz or heavier; fine-pitch, high-density inner layers sometimes use lighter 0.5 oz copper.
It is a legacy of the manufacturing process: copper foil is produced and specified by the weight of a standard one-square-foot sheet at a given thickness, and the industry has kept this convention even though it now behaves purely as a thickness specification.
No, not necessarily — designers can (and often do) specify different copper weights for different layers within the same board, for example heavier copper on outer power layers and lighter copper on fine-pitch inner signal layers.
Thicker copper directly increases a trace's cross-sectional area for the same width, which raises its current-carrying capacity (ampacity) under the IPC-2221 formula — see the Trace Width calculator to see the exact effect.
Resistance is inversely proportional to cross-sectional area, so doubling the copper weight (thickness) for the same trace width roughly halves its resistance and voltage drop — see the Trace Resistance calculator.
Yes, generally. Heavier copper weights typically increase PCB manufacturing cost somewhat and can also require wider minimum trace/space design rules, since etching thick copper precisely into narrow features is more difficult than with standard 1 oz copper.
2 oz is a common step-up choice for moderate power designs needing more current capacity than 1 oz easily provides in the available board space; very high-current designs may go to 3 oz, 4 oz or beyond, or use dedicated busbars instead of traces.
Very close but not exactly — the precise conversion is 1 oz ≈ 34.79 µm, which is universally rounded to 35 µm in practice since the difference is negligible for design purposes.
Simply take the resulting thickness (in mils or µm/mm) and enter it, or the corresponding oz weight, into the Trace Width, Trace Resistance, or Thermal Via calculators, which all accept copper weight or thickness as an input.
Trace Width Calculator • Trace Resistance & Voltage Drop • Via Current Capacity • All Calculators