PCB Trace Width Calculator

The IPC-2221 standard is the industry reference for PCB current-carrying capacity. The empirical formula dates back to 1950s military research on the temperature rise of PCB conductors. Modern data shows it's quite conservative — most designs can safely carry 50-100% more current. However, for commercial and safety-critical designs, sticking with IPC-2221 values provides a well-documented margin against manufacturing variation, thermal cycling, and mechanical stress.

Key caveats: the formula assumes still air, ambient temperature, and no thermal vias or copper pours nearby. In practice, large ground pours, thermal vias, and even adjacent traces affect heat dissipation. For hot spots, CAD tools with thermal simulation give more accurate predictions.

The printed circuit board was patented by Austrian engineer Paul Eisler in 1943 while living in the UK, initially for wartime radio manufacture. Early PCBs were single-sided with point-to-point copper etched on phenolic resin. The double-sided plated-through-hole process arrived in the late 1950s at Motorola and Hughes Aircraft, and multilayer PCBs emerged in the mid-1960s alongside the first integrated circuits.

The IPC (Institute of Printed Circuits, now Association Connecting Electronics Industries) issued IPC-D-275 in 1963 — the ancestor of today's IPC-2221 — defining conductor spacing, current capacity, and fabrication tolerances. The current-vs-width curves were developed from empirical measurements by the US Bureau of Standards in the 1950s and have remained essentially unchanged, despite better FR4 substrates and plating uniformity.

Modern PCB design routinely violates 1960s-era assumptions: thermal vias act as mini-heatsinks, ground pours spread heat laterally, and high-density interconnect (HDI) boards operate above their nominal derating. Tools like Saturn PCB Design, Polar Si9000, and Altium's built-in calculators still default to IPC-2221 because it's a published, defensible reference — even when conservative.

Enter the current, temperature rise (10°C conservative, 30°C aggressive), copper weight in ounces (1 oz = 35 µm), and layer type (external dissipates better than internal). The tool solves the IPC-2221 formula A = (I / (k × ΔT^0.44))^(1/0.725) for cross-sectional area, then divides by copper thickness to get width. Constants: k = 0.048 external, 0.024 internal.

Optional trace length adds a voltage drop estimate using copper resistivity ρ = 17.24 nΩ·m. For power-integrity work, allow at least 2× the IPC-2221 minimum on high-di/dt traces (switching converter outputs) so that inductance and skin effect don't dominate. Everything runs client-side; no values leave your browser.