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PCB Trace Width Calculator

Calculate the required trace width, resistance, voltage drop, and power loss for your PCB design based on the IPC-2221 standard. Ensure high-speed signal integrity and reliable power delivery before manufacturing.

Design Parameters

A

Used to calculate resistance, voltage drop, and power loss below.

Calculations are based on the IPC-2221 generic standard. For highly complex HDI or RF designs, consult with NextPCB engineers.

Recommended Trace Width

 

External Layers

W
0.00 mil

Trace in direct contact with air

0.00 mΩ
Resistance
0.00 V
Volt. Drop
0.00 W
Power Loss
 

Internal Layers

W
0.00 mil

Trace embedded within dielectric

0.00 mΩ
Resistance
0.00 V
Volt. Drop
0.00 W
Power Loss

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IPC-2221 Calculation Reference

The width calculations utilize the standard IPC-2221 formulas. The required cross-sectional area is determined first, followed by the trace width derived from the selected copper thickness.

  • k = 0.048 for External Layers
  • k = 0.024 for Internal Layers
Area (mils²) = ( Current / ( k * TempRise0.44 ) ) (1/0.725)
Width (mils) = Area / ( CopperThickness_oz * 1.378 )

Once the width is known, resistance, voltage drop, and power loss are calculated from the trace's physical dimensions and copper's resistivity, corrected for the trace's estimated operating temperature (Ambient + Temp Rise).

  • ρ (copper @ 25°C) = 1.7 × 10⁻⁶ Ω·cm
  • α (temp. coefficient) = 0.0039 / °C
Resistance (Ω) = ρ * Length / ( Width * Thickness ) * ( 1 + α * ( Ttrace - 25 ) )
Voltage Drop (V) = Current * Resistance
Power Loss (W) = Current² * Resistance

Frequently Asked Questions

Why do internal layer traces need to be wider than external layer traces for the same current?

External traces are exposed to open air, which convects heat away efficiently. Internal traces are sandwiched between dielectric layers, which are much poorer thermal conductors, so heat builds up faster. To stay within the same allowed temperature rise, IPC-2221 uses a lower constant (k = 0.024 for internal vs. k = 0.048 for external), which results in a wider trace for a given current.

What temperature rise value should I use?

10°C is a common conservative default for general-purpose designs. Higher-reliability designs, or traces near heat-sensitive components, often use lower values (5-10°C), while traces with more thermal headroom can use 20-30°C to save board space. Check your design's thermal budget and any applicable industry or safety standards before finalizing this value.

Does IPC-2221 account for trace resistance, voltage drop, or power loss directly?

No. IPC-2221 only defines the current-carrying capacity relationship between trace width, copper thickness, and allowed temperature rise. Resistance, voltage drop, and power loss are calculated separately using the trace's physical dimensions and copper resistivity, which is why this calculator computes them as an additional step after determining the IPC-2221 width.

Is the IPC-2221 formula accurate for all trace widths and currents?

IPC-2221's generic formula is a widely used industry approximation derived from empirical test data, and it is most accurate within the current and width ranges covered by that original testing. For very high currents, heavy copper (over 3oz), or high-density designs, many engineers add a safety margin or reference IPC-2152, which accounts for additional variables such as trace thickness, board thickness, and adjacent copper pours.

Why does trace resistance increase at higher temperatures?

Copper's resistivity rises with temperature at a rate of roughly 0.393% per °C. As current flows through a trace, resistive heating raises its temperature above ambient, which in turn increases its resistance. This calculator applies that temperature coefficient so the resistance, voltage drop, and power loss figures reflect the trace's actual operating temperature rather than its resistance at room temperature.

How much voltage drop is acceptable on a PCB trace?

This depends on the circuit's sensitivity. Power traces are often designed to keep voltage drop under 2-3% of the supply voltage, while traces feeding precision analog or low-voltage digital circuits may need a much tighter margin. If the calculated voltage drop is too high, widening the trace, shortening the path, or moving to a heavier copper weight are the usual fixes.