PCB Trace Width Calculator

The PCB Trace Width Calculator determines the minimum copper trace width required to safely carry a given current on a printed circuit board without excessive heating. When you design your own PCBs for maker projects — whether using KiCad, EasyEDA, or Fritzing — getting trace width right is essential for both safety and reliability. Too narrow a trace overheats and can delaminate or burn. Too wide wastes precious board space and raises fabrication cost.

PCB copper traces are thin conductors with real resistance, and current flowing through resistance generates heat (P = I²R). At low currents (below 500mA), standard 0.25mm (10 mil) signal traces are more than adequate and are routinely used for Arduino GPIO, SPI, I2C, and UART connections. At higher currents — motor drivers, power rails, battery charging circuits, LED power lines — trace width must be specifically calculated.

This calculator implements the IPC-2221 standard formula, which is the industry-accepted method for trace width calculation used by professional PCB engineers. The formula relates current (I), temperature rise (ΔT), and cross-sectional area (A): I = k × ΔT^b × A^c, where k, b, and c are empirical constants that differ for external (outer layer) and internal traces. External traces benefit from natural convection and radiation cooling; internal traces are sandwiched between substrate layers with reduced thermal dissipation, requiring wider traces for the same current.

Copper thickness is specified in oz/ft² — a weight per area measurement that correlates to physical thickness. Standard PCB copper is 1 oz/ft², corresponding to approximately 35 µm (1.378 mil) thickness. 2 oz copper is 70 µm thick and can carry roughly 40% more current at the same width. Most budget PCB manufacturers (JLCPCB, PCBWay, OSHPark) offer 1 oz copper as standard. 2 oz copper is available as an upgrade and is recommended for power electronics.

Temperature rise is the permissible increase in trace temperature above ambient. IPC-2221 defines two common values: 10°C rise is conservative and recommended for general use — your board stays cool and component lifetimes are maximized. 20°C rise allows narrower traces but the board runs noticeably warm. For outdoor or high-reliability applications, stick to 10°C. For compact boards where space is premium, 20°C is acceptable. Never design for more than 30–40°C rise in commercial products.

For hobby projects, practical minimum trace widths to remember: signal traces (logic, SPI, I2C, UART) — 0.2–0.25mm (8–10 mil) is the PCB fab minimum for most services; power traces at 1A — use 0.5mm (20 mil) with 1 oz copper; power traces at 2A — use 1mm (40 mil); power traces at 5A — use 2.5mm (100 mil); ground planes — use fills/pours rather than traces. Always add 25–50% extra width beyond the calculated minimum for real-world margin.

Trace resistance is also provided because it affects voltage drop in power rails. A long, narrow 5V power trace serving multiple components can drop significant voltage, causing the far end of the board to receive less than 5V. For a 10cm trace at 1A, knowing the resistance lets you calculate the voltage drop (V = IR) and assess whether it impacts circuit operation. For sensitive analog circuits, minimize trace resistance in reference voltage paths.