PCB Trace Width Calculator
Estimate required trace width from current, copper weight, and allowed temperature rise (IPC-2221 style equation).
What this PCB calculator does
This tool helps you estimate how wide a PCB trace should be to carry a chosen current without exceeding your allowed temperature rise. It also gives an approximate voltage drop and power loss for a given trace length.
The calculator uses a well-known IPC-2221 empirical equation. It is useful for quick sizing during early design, quote prep, or educational use. For high-reliability products, always validate with your PCB manufacturer and thermal testing.
Inputs explained
1) Current (A)
Enter the continuous current the trace must carry. If your load is pulsed, use RMS or worst-case continuous equivalent unless you have a thermal simulation that proves otherwise.
2) Allowed temperature rise (°C)
This is how much hotter the trace can be than ambient. Lower rise means a wider trace. Common quick-design values are 10°C to 20°C.
3) Copper weight (oz/ft²)
Copper thickness directly affects cross-sectional area. Typical values:
- 0.5 oz ≈ 0.69 mil
- 1 oz ≈ 1.38 mil
- 2 oz ≈ 2.76 mil
4) Layer type
External traces cool better than internal traces. For the same current and rise, internal traces generally require more width.
Quick design guidance
- Use generous width for power rails whenever board space allows.
- For high current, consider copper pours, polygons, or parallel traces.
- Keep return paths short and low impedance to reduce noise and heating.
- Via count matters: current bottlenecks often occur at vias, not just traces.
- Check connector, terminal, and fuse temperature limits too.
Important limitations
IPC-2221 equations are conservative in some situations and optimistic in others. Real thermal behavior depends on board stackup, nearby copper, airflow, enclosure, duty cycle, and ambient temperature. If your product is safety critical or power dense, treat this calculator as a starting point and confirm with:
- IPC-2152 based methods or field solver tools
- Lab measurements (IR camera or thermocouples)
- Manufacturer DFM guidance and derating rules
Practical example
Suppose you need to carry 3 A on an outer layer, with 1 oz copper and 15°C rise target. This calculator might suggest around the low-millimeter range width. If space allows, adding extra margin can reduce voltage drop, lower heat, and improve long-term reliability.
Bottom line
A good PCB trace width calculation balances electrical performance, thermal safety, and board area. Use this tool for fast estimates, then verify in context with the full design.