PCB Trace Width Calculator
Uses IPC-2221 empirical equations for quick estimation. Final designs should be verified with IPC-2152 curves, your PCB manufacturer, and thermal testing.
Why use a PCB trace calculator?
A PCB trace calculator helps you estimate how wide a copper trace should be to safely carry current without overheating. If traces are too narrow, they can run hot, increase voltage drop, and in extreme cases fail. If they are too wide, you may waste valuable board space and routing flexibility.
This tool is especially useful during early layout planning when you need a fast, practical answer for current carrying capacity, copper thickness, and thermal rise targets.
How this calculator works
Equation used
The calculator uses the classic IPC-2221 relationship:
I = k × (ΔT)0.44 × A0.725
- I = current in amps
- ΔT = allowable temperature rise above ambient (°C)
- A = copper cross-sectional area (mil²)
- k = 0.048 (external traces) or 0.024 (internal traces)
From area, the tool computes width using your selected copper thickness, then estimates resistance and voltage drop over the entered trace length.
What each input means
- Current (A): continuous current expected through the trace.
- Temperature rise (°C): how much hotter than ambient you allow the trace to get.
- Copper thickness (oz): copper weight on the PCB layer.
- Layer type: internal layers dissipate heat less effectively than external layers.
- Trace length: used to estimate resistance and voltage drop.
- Existing width: optional check to compare your actual routed width versus recommended width.
Practical design guidance
External vs internal traces
External traces can release heat to air and solder mask surroundings better than internal traces buried between prepreg layers. For the same current and temperature rise target, internal traces usually need to be significantly wider.
Choose realistic temperature rise targets
Common design choices are 10°C to 20°C rise for power paths. High-reliability or thermally sensitive products often target lower rise to improve long-term performance.
Account for voltage drop, not just heat
Even when a trace is thermally safe, it can still introduce unacceptable voltage loss in low-voltage systems. This matters in motor drivers, LED arrays, battery-powered devices, and high-current regulators.
Example use case
Suppose you need to carry 2 A on an external 1 oz trace with 10°C rise. Enter those values and the calculator returns a minimum recommended width in mm and mil. If your routed width is smaller, the comparison result warns you and estimates the current that width can support under the same assumptions.
Common mistakes to avoid
- Using default values without checking real operating conditions.
- Ignoring copper thickness changes between prototypes and production.
- Assuming short pulses equal continuous current ratings.
- Forgetting connectors, vias, and polygons can become the real bottleneck.
- Not validating thermal behavior in actual enclosure airflow conditions.
FAQ
Is this calculator enough for final sign-off?
It is a strong first-pass estimate. For final release, validate with IPC-2152 guidance, manufacturer stackup data, and hardware measurements.
Does wider always mean better?
Electrically and thermally, wider traces usually help. But over-widening can complicate routing density, impedance goals, and component fan-out, so optimize for your real constraints.
What about vias in high-current paths?
Vias add resistance and thermal limits. Use multiple vias, larger drill sizes, and copper pours when moving current between layers.
Bottom line
A reliable PCB power layout starts with proper trace sizing. Use this PCB trace calculator early, review the resulting width and voltage drop, and then refine your layout with DFM checks and thermal verification before production.