PCB Trace Current
Calculate the maximum current a PCB trace can carry using the IPC-2221 standard. Enter trace width, copper thickness, and temperature rise for instant results with cross-section area, resistance, and voltage drop.
Additional Inputs
About This Calculator
The PCB Trace Current Calculator helps PCB designers and electronics engineers determine how much current a copper trace on a printed circuit board can safely carry. Using the industry-standard IPC-2221 formula, this calculator accounts for trace geometry, copper thickness, temperature rise, and whether the trace is on an external or internal layer.
The IPC-2221 formula used is: I = k × ΔT^0.44 × A^0.725, where I is the maximum current in amperes, k is the trace location coefficient (0.048 for external, 0.024 for internal), ΔT is the temperature rise in °C, and A is the cross-sectional area in square mils. The cross-sectional area is calculated as the product of trace width and copper thickness, where 1 oz/ft² copper is approximately 1.378 mils (35 µm) thick.
When additional inputs like ambient temperature and trace length are provided, the calculator also computes trace operating temperature, DC resistance (with copper temperature coefficient correction), voltage drop via Ohm's Law, and power dissipation. This makes it a comprehensive tool for verifying PCB power distribution networks and ensuring traces stay within safe thermal limits.
Regional Notes
All regions (Global): The IPC-2221 standard is universally adopted in the electronics industry worldwide. PCB manufacturers in India, the US, UK, and most countries fabricate boards to IPC standards. Copper weights (oz/ft²) are standardized globally — 1 oz/ft² copper is always 35 µm regardless of region. Trace width is commonly specified in either mm or mils; this calculator accepts mm input and converts internally. Ambient temperature should be set to the expected operating environment (25 °C for room temperature, higher for enclosed or industrial applications).
Frequently Asked Questions
How much current can a PCB trace carry?
The current a PCB trace can carry depends on its width, copper thickness, temperature rise, and whether the trace is on an external or internal layer. Using the IPC-2221 standard, a 1 oz external trace of 1 mm width with a 10 °C temperature rise can carry approximately 1.5 A. Wider traces, thicker copper, and higher allowed temperature rises all increase current capacity.
What is the IPC-2221 standard for PCB current capacity?
IPC-2221 is the industry standard that defines the relationship between PCB trace current, cross-sectional area, and temperature rise. The formula is I = k × ΔT^0.44 × A^0.725, where k is 0.048 for external traces and 0.024 for internal traces, ΔT is the temperature rise in °C, and A is the cross-sectional area in square mils.
What is the difference between internal and external PCB traces?
External traces are on the outer layers of a PCB and can dissipate heat directly into the air, allowing them to carry more current. Internal traces are buried within the PCB substrate and have poorer heat dissipation, so they carry approximately half the current of an equivalent external trace. The IPC-2221 standard uses k = 0.048 for external and k = 0.024 for internal traces.
How does copper thickness affect PCB trace current capacity?
Thicker copper increases the cross-sectional area of the trace, which reduces resistance and allows higher current flow. Standard PCB copper thicknesses are 0.5 oz, 1 oz, and 2 oz per square foot. A 2 oz trace can carry roughly 40% more current than a 1 oz trace of the same width and temperature rise.
What happens if a PCB trace carries too much current?
Excessive current causes resistive heating that raises the trace temperature beyond safe limits. This can damage the PCB laminate, cause the copper trace to delaminate, melt solder joints, create open circuits, or even cause a fire. Always use a sufficient safety margin when determining trace widths for your expected operating current.
How do I calculate PCB trace voltage drop?
Voltage drop is calculated using Ohm's Law: V = I × R. The trace resistance depends on the copper resistivity (1.724 × 10⁻⁶ Ω·cm at 20 °C), trace length, cross-sectional area, and operating temperature. Copper's temperature coefficient of 0.0039 per °C means resistance increases by about 0.4% for every 1 °C rise above 20 °C.
What is a safe temperature rise for PCB traces?
A 10 °C temperature rise is conservative and suitable for most consumer electronics. Industrial applications often use 20 °C, while high-reliability designs may limit rise to 5 °C. The maximum safe temperature depends on the PCB material's glass transition temperature (Tg), typically 130-180 °C for standard FR-4.
What is the standard copper thickness for PCB traces?
Standard PCB copper thickness is 1 oz per square foot, which corresponds to approximately 35 µm (0.035 mm or 1.378 mils). Other common options include 0.5 oz (17.5 µm) for fine-pitch designs and 2 oz (70 µm) or 3 oz (105 µm) for high-current power applications. Heavy copper PCBs can use 4 oz to 10 oz or more.