When designing printed circuit boards (PCBs), the width of each copper trace determines how much current it can safely carry without overheating. Traces that are too narrow create excessive resistance, leading to voltage drops and possibly causing the copper to delaminate or burn. On the other hand, overly wide traces waste valuable board space and can crowd out components or routing paths. This calculator helps you strike the right balance by estimating the minimum width for a desired current level and temperature rise.
The thickness of PCB copper is usually specified in ounces per square foot. One ounce of copper corresponds to a thickness of approximately 35 micrometers, or 1.4 mils. Thicker copper allows higher current for a given width because it has greater cross-sectional area. Common PCB fabrication services offer 1 oz or 2 oz copper layers, though heavier weights such as 3 oz or 4 oz are available for power electronics. By adjusting the copper thickness field, you can explore how selecting a heavier copper weight reduces the width requirements.
Modern PCB designers often reference the IPC-2152 standard for trace temperature calculations. The standard provides empirical charts correlating current, cross-sectional area, and temperature rise based on lab measurements. While the curves are precise, manually reading them can be time consuming. This calculator uses a simplified equation derived from those charts. The constant k approximates external trace conditions, where heat can dissipate more easily than internal layers. The formula estimates the needed cross-sectional area, then divides by copper thickness to get width. Although simplified, it offers a reasonable starting point for typical design scenarios.
Begin by entering the maximum current the trace will carry. For digital circuits, currents may be as low as a few milliamps, while power converters can exceed tens of amps. Next, specify the copper thickness in ounces. If you prefer to think in micrometers or mils, you can convert your value to ounces using a quick lookup: 1 oz is about 35 µm or 1.4 mils. Finally, decide how much temperature rise you are willing to allow. A common choice is 10 °C, balancing reliability with board real estate. If you anticipate higher ambient temperatures or less airflow, you might target a smaller rise to keep components cooler.
The equation used is A = (I / (0.024 * rise0.44))(1/0.725), where A is the cross-sectional area in square mils, I is the current in amps, and rise is the allowed temperature increase in Celsius. This expression roughly matches the IPC-2152 external trace data for a 20 °C ambient condition. Once the area is known, the width is simply A divided by the copper thickness (also converted to mils). If you choose millimeters as the output, the calculator converts from mils to mm at the end. Keep in mind that internal layers dissipate heat less effectively, so they often require wider traces than this calculator predicts.
Imagine a microcontroller board with a 2 amp motor driver. You select 2 oz copper to handle the current with a moderate trace width. Plugging in 2 amps, 2 oz copper, and a 10 °C rise yields a recommended width of around 28 mils, or roughly 0.7 millimeters. If you reduce the copper to 1 oz, the width jumps to about 56 mils. By experimenting with these values, you can decide whether upgrading the copper weight or adjusting layout space is the better tradeoff for your design.
Trace width is only one factor in PCB current capacity. The length of the trace, type of solder mask, presence of thermal reliefs, and whether the board has a dedicated plane for heat spreading all influence operating temperature. In high-current applications, designers may use multiple parallel traces, larger copper pours, or even external copper bars to handle heavy loads. If your design will see rapid temperature cycling or extreme ambient conditions, consider building in extra margin beyond the bare minimum. Many engineers choose a width slightly larger than calculated to improve reliability and accommodate manufacturing tolerances.
Determining the right trace width ensures your PCB will operate safely and efficiently. With this calculator, you can quickly gauge how copper weight and temperature rise affect the minimum width for a given current. Use the results as a baseline, then adjust based on your specific design constraints. Careful planning now prevents expensive board re-spins later and keeps your electronics running smoothly.
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