PCB Trace Resistance Calculator
Calculate the DC resistance of a PCB trace based on length, width, thickness, and material resistivity. Determine voltage drop and power loss in traces.
1 oz = 0.035mm, 2 oz = 0.07mm
Copper: 1.7×10⁻⁸ Ω·m (0.000000017)
How to Use This Calculator
- Enter the trace length in millimeters.
- Enter the trace width in millimeters.
- Enter the trace thickness (copper thickness, typically 0.035mm for 1 oz).
- Enter the material resistivity (default: 1.7×10⁻⁸ Ω·m for copper).
- The calculator displays the DC resistance in ohms.
Trace Resistance Formula
DC resistance is calculated from resistivity, length, and cross-sectional area:
Where A = W × T (width × thickness)
Where R = resistance (Ω), ρ = resistivity (Ω·m), L = length (m), A = cross-sectional area (m²). Example: 50mm length, 0.5mm width, 0.035mm thickness, copper: R = (1.7×10⁻⁸ × 0.05) / (0.0005 × 0.000035) = 0.0486Ω.
Full Description
PCB trace resistance is an important consideration in circuit design, especially for power traces and high-current paths. Resistance causes voltage drop (V = I × R) and power loss (P = I² × R), which can affect circuit performance and cause heating. Understanding trace resistance helps you design efficient, reliable circuits.
Resistance depends on four factors: material resistivity (copper is 1.7×10⁻⁸ Ω·m), trace length (longer traces have more resistance), trace width (wider traces have less resistance), and trace thickness (thicker traces have less resistance). For power traces carrying significant current, resistance must be kept low to minimize voltage drop and heating. This often requires wider, thicker traces or multiple parallel traces.
This calculator helps you determine trace resistance. Enter length, width, thickness, and resistivity, and it calculates the DC resistance. Use it when designing power traces, calculating voltage drops, estimating power loss, or understanding how trace dimensions affect resistance. Remember that resistance increases with temperature, so account for operating temperature in critical applications.
Frequently Asked Questions
How is trace resistance calculated?
Resistance = (Resistivity × Length) / Cross-sectional Area. For PCB traces: R = (ρ × L) / (W × T), where ρ = resistivity (1.7×10⁻⁸ Ω·m for copper), L = length, W = width, T = thickness. All in consistent units.
What is the resistivity of copper?
Copper resistivity = 1.7×10⁻⁸ Ω·m (0.000000017 Ω·m) at 20°C. Resistivity increases with temperature (~0.4% per °C). For PCBs, use 1.7×10⁻⁸ Ω·m unless working at elevated temperatures.
How does trace resistance affect circuits?
Trace resistance causes voltage drop (V = I × R) and power loss (P = I² × R). For high-current traces, resistance can cause significant voltage drop and heating. Keep resistance low by using wider, thicker traces for power paths.
What is an acceptable trace resistance?
Depends on application. Power traces: <0.1Ω for most applications. Signal traces: Usually negligible unless very long or very thin. Calculate voltage drop: V = I × R. If voltage drop is acceptable, resistance is fine. For 5V power at 1A, keep R < 0.05Ω to limit drop to 50mV.