PCB Trace Width Calculator
Calculate minimum trace width for any current using the IPC-2221 standard.
Component Values
Results
IPC-2221 trace cross-section
Trace Width vs Current
Trace width vs current (1 oz copper)
Reference: Trace Width at 10°C Rise, 1oz Copper (External)
| Current (I) | Min. Width (mils) | Min. Width (mm) |
|---|---|---|
| 0.5 A | 4.5 mils | 0.12 mm |
| 1 A | 11.8 mils | 0.30 mm |
| 2 A | 30.8 mils | 0.78 mm |
| 5 A | 108.9 mils | 2.77 mm |
| 10 A | 283.2 mils | 7.19 mm |
IPC-2221 formula: Area = (I / (k × ΔT^0.44))^(1/0.725) mils², k=0.048 external, k=0.024 internal.
PCB Trace Width — IPC-2221
The IPC-2221 standard provides the industry-standard formula for calculating PCB trace width based on current carrying capacity and allowable temperature rise: Area (mils²) = (I / (k × ΔT^0.44))^(1/0.725). For external traces k=0.048, for internal traces k=0.024.
After calculating the cross-sectional area in mils², divide by the copper thickness in mils to get the minimum width. 1 oz copper = 1.378 mils (35 µm). 2 oz = 2.756 mils (70 µm). Always add 20–50% margin for real-world manufacturing variations.
External traces dissipate heat through convection and radiation, so they can carry more current for the same width compared to internal traces sandwiched between FR4 layers. For power traces, always add vias if the trace needs to carry more than its width allows.
IPC-2221 Width Formula
Area = (I / (k × ΔT^0.44))^(1/0.725)Width (mils) = Area / thicknessk values
External: k = 0.048 | Internal: k = 0.024Key Points
- IPC-2221 is the industry standard for PCB trace sizing
- External traces run cooler than internal — use k=0.048 vs k=0.024
- 1 oz copper = 35 µm = 1.378 mils thickness
- Always add 20–50% width margin for safety
- Temperature rise of 10°C is a common conservative target
- For >10A: consider 2oz copper or wider traces with vias
Applications
- Power supply PCB design (motor drivers, DC-DC converters)
- USB power delivery trace sizing (5A)
- Battery protection circuit traces
- LED driver and high-current switching circuits
- RF ground planes and power pours
FAQ
How wide should PCB traces be?
Signal traces (< 100 mA) can be as narrow as 0.1 mm. Power traces must be sized using IPC-2221. For 1 A at 10°C rise with 1 oz copper: ~0.6 mm (24 mils) external, ~1.3 mm (52 mils) internal.
What is the minimum trace width for 1A?
Using IPC-2221 at ΔT=10°C, 1oz copper, external layer: minimum width ≈ 24 mils (0.6 mm). For internal layers, it approximately doubles to ~52 mils (1.3 mm). Always add a safety margin.
How to calculate PCB trace width for high current?
Use IPC-2221: Area = (I / (k × ΔT^0.44))^(1/0.725), Width = Area / thickness_mils. For high current (>5A), consider 2oz copper, multiple vias, or a copper pour.
What is IPC-2221 standard?
IPC-2221 is the Generic Standard on Printed Board Design published by IPC. It provides formulas for PCB trace current carrying capacity based on cross-sectional area, temperature rise, and whether the trace is on an external or internal layer.
How does copper thickness affect trace current capacity?
Doubling copper thickness (e.g., 1oz to 2oz) doubles the cross-sectional area for the same width, doubling current capacity. Alternatively, you can achieve the same current in a narrower trace, saving board space.
What is the difference between internal and external PCB traces?
External traces (top/bottom layers) can cool by convection. Internal traces are embedded in FR4 with no airflow. IPC-2221 uses k=0.048 for external and k=0.024 for internal, meaning internal traces need to be about twice as wide for the same current.
Did you know? IPC-2221 trace width guidelines were originally derived from empirical charts developed in the 1950s and 1960s for military electronics. The 2021 revision updated the equations with more accurate thermal modelling, but the underlying physics — resistive heating in copper — has not changed.