4A Trace Width Calculator
1oz Copper | Internal Layer | IPC-2221
For 4A current on 1oz copper internal layer with 10°C temperature rise:
Input Parameters
MOD: TR_WID_V1Results
Analysis & Recommendations
Design Guidance
- •4A on Internal layer, min width: 5.32mm
- •Add 10-20% safety margin. Recommended: 6.12mm
- •Cross-sectional area: 286.89 mil² (0.1851 mm²)
Electrical Impact
- •Resistance (10mm trace): 0.97 mΩ
- •Voltage drop: 3.87 mV
- •Power dissipation: 15.49 mW
IPC-2221 Calculation Method
This calculation uses the IPC-2221 standard formula: I = k × ΔT^b × A^c where k=0.024, b=0.44, c=0.725. Internal layers use lower k-value due to reduced heat dissipation
Understanding 4A Trace Width Requirements
When designing a PCB that needs to carry 4 amperes of current, proper trace width calculation is critical for thermal management and reliability. Based on the IPC-2221 standard, a 1oz copper internal layer trace requires approximately 5.32mm (209.4 mil) width to safely handle this current with a 10°C temperature rise. This calculation ensures your printed circuit board maintains optimal performance without excessive heating, which could lead to solder joint failure, delamination, or fire hazards in extreme cases.
Key Parameters for 4A Design
- Current Capacity: 4A (amperes) - the maximum continuous current this trace is designed to carry
- Copper Weight: 1 oz/ft² (35μm) - determines the conductor cross-sectional area
- Layer Type: Internal ( sandwiched between FR4 dielectric material)
- Temperature Rise: 10°C above ambient (IPC-2221 conservative design guideline)
- Cross-Section Area: 286.89 sq mil (0.1851 mm²)
Why Layer Type Matters for 4A Current
Internal layers are sandwiched between FR4 dielectric material, which has relatively poor thermal conductivity (~0.3 W/m·K). For 4A on 1oz copper internal layer, the trace must be wider to compensate for reduced heat dissipation. The calculated width of 5.32mm is the IPC-2221 estimate for this current; confirm against your fabricator's capability and your own thermal margin.
IPC-2221 Standard Formula
The IPC-2221B standard provides the industry-accepted formula for PCB trace width calculation: I = k × ΔT^b × A^c, where I is current in amperes, ΔT is temperature rise in °C, A is cross-sectional area in square mils, and k, b, c are empirical constants specific to internal layers. This is the empirical IPC-2221 relationship this calculator implements; real boards also depend on copper thickness tolerance, airflow and neighbouring traces, so treat the result as an estimate.
4 A compared with other design choices
All figures come from the same IPC-2221 function as the calculator above, with a 100 mm run for resistance values.
| Copper | External (mm) | Internal (mm) |
|---|---|---|
| 0.5 oz | 4.09 | 10.64 |
| 1 oz | 2.04 | 5.32 |
| 2 oz | 1.02 | 2.66 |
| Rise | Width (mm) | R per 100 mm (mΩ) | Drop (mV) | Loss (mW) |
|---|---|---|---|---|
| 10 °C | 5.32 | 9.68 | 38.7 | 155 |
| 20 °C | 3.49 | 15.30 | 61.2 | 245 |
| 30 °C | 2.73 | 20.28 | 81.1 | 325 |
At the 10 °C design point a 100 mm run of this trace has 9.68 mΩ resistance (copper at 10 °C above 20 °C), drops 38.7 mV and dissipates 155 mW. Resistance, drop and loss scale linearly with trace length.
Next steps for a 4 A net: size layer-change vias for 4 A (vias need their own hole, plating and board-thickness inputs, so nothing is prefilled) or check the voltage drop of a long 4 A run.
Neighbouring currents on the same copper and layer: 3 A (3.58 mm), 5 A (7.24 mm).
Typical Applications for 4A Traces
Frequently Asked Questions
Can I use a narrower trace than 5.32mm for 4A?
Using a narrower trace will increase temperature rise beyond 10°C. While acceptable for some applications, exceeding 20-30°C rise can affect solder joint reliability and nearby component performance. Consider using thicker copper (e.g., 2oz) or parallel traces for high-reliability designs.
How does ambient temperature affect this calculation?
The IPC-2221 formula calculates temperature RISE above ambient. If your board operates in a 50°C environment with 10°C rise, the trace will reach 60°C. For high-ambient applications, design for lower temperature rise to maintain adequate safety margins.
Should I add thermal vias for 4A traces?
Thermal vias can significantly improve heat dissipation, especially for internal layer traces. For 4A and above, consider adding vias connecting to ground planes for additional thermal spreading. Use our via current calculator to properly size thermal vias.
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