IPC-2221 vs IPC-2152: Which to Use?

If you've ever tried to calculate the right trace width for your PCB, you've probably stumbled upon two standards: IPC-2221 and IPC-2152. Both claim to help you figure out how much current your traces can handle—but they give different results. So which one should you actually use?

The short answer: it depends on your project. The longer answer involves understanding the history, methodology, and practical implications of each standard. Let's break it down so you can make an informed decision for your next design.

What Are IPC-2221 and IPC-2152?

Both standards come from the IPC (Institute for Printed Circuits), the industry body that sets guidelines for PCB design and manufacturing. However, they were created at different times and with different methodologies.

Key Differences at a Glance

Before we dive into the technical details, here's a quick comparison of the two standards:

The IPC-2221 Formula Explained

The IPC-2221 approach uses a straightforward empirical formula to calculate the relationship between current, temperature rise, and conductor cross-sectional area:

Where:

• I = Current in Amps
• k = Constant (0.048 for external layers, 0.024 for internal layers)
• ΔT = Temperature rise above ambient in °C
• A = Cross-sectional area of the trace in mil²

Notice how the constant k is halved for internal layers? That's because internal traces are sandwiched between FR4 material, which is a poor thermal conductor compared to air. They can't dissipate heat as effectively, so they need to be wider to carry the same current.

The IPC-2152 Approach: Charts and Correction Factors

IPC-2152 doesn't give you a neat formula to plug numbers into. Instead, it provides a series of charts based on actual measurements and thermal modeling. The basic process involves:

1. Find the baseline cross-sectional area from the universal chart for your current and temperature rise.
2. Apply copper thickness modifier based on your actual copper weight (0.5oz, 1oz, 2oz, etc.).
3. Apply board thickness modifier since thicker boards dissipate heat differently.
4. Apply plane proximity modifier if your trace is near a copper pour or ground plane.
5. Calculate final trace width from the modified cross-sectional area.

This multi-step process sounds complex, but modern PCB trace width calculators can handle it automatically, giving you more accurate results than the old IPC-2221 formula.

How Different Are the Results?

Here's where it gets interesting. Let's compare the calculated trace widths for some common scenarios using both standards:

As you can see, IPC-2152 generally allows narrower traces than IPC-2221 for the same current capacity. This is because:

• IPC-2152 accounts for the heat-spreading effect of nearby copper planes
• Modern PCB manufacturing is more consistent than 1950s production
• IPC-2221 was intentionally conservative to provide a safety margin

When to Use IPC-2221 vs IPC-2152

Real-World Example: 5A Power Trace Design

Let's walk through a practical example. You're designing a motor driver board that needs to carry 5A on an external layer trace. The board uses 1oz copper, and you want to limit temperature rise to 10°C.

In this case, IPC-2152 allows a trace that's about 22% narrower than IPC-2221 would suggest—a significant saving when you're trying to route power through a crowded board.

Want to try these calculations yourself? Use our free PCB Trace Width Calculator which supports both IPC-2221 and IPC-2152 standards.

Common Misconceptions

Internal vs External Layer Considerations

Both standards treat internal and external layers differently, but the magnitude of the difference varies:

This is another area where IPC-2152 provides more nuanced guidance. The newer standard accounts for the fact that modern multilayer PCBs often have internal planes that help dissipate heat from inner layer traces. Learn more about layer selection in our guide on Internal vs External PCB Layers.

How Copper Weight Affects Your Choice

The choice of copper weight significantly impacts trace width requirements, and both standards handle this differently:

Thicker copper means you can use narrower traces for the same current. For a deep dive into copper weight selection, check out our Copper Weight Comparison Guide.

Using Online Calculators

Nobody wants to manually extract values from logarithmic charts. Fortunately, several online tools implement these standards:

Quick Decision Guide

Conclusion

Both IPC-2221 and IPC-2152 are valid tools in a PCB designer's toolkit. IPC-2221 offers simplicity and conservative estimates that have served the industry for decades. IPC-2152 provides more accurate results for modern PCB designs, especially those with copper pours and multilayer stackups.

For most professional designs today, IPC-2152 is the better choice when you need accurate trace width calculations. But don't throw away IPC-2221 entirely—it's still useful for quick sanity checks and when you want that extra margin of safety.

The best approach? Use a calculator that supports both standards, compare the results, and choose based on your specific application requirements. After all, the goal isn't to follow a standard blindly—it's to design a PCB that works reliably in the real world.