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PCB Trace Resistance Calculator

Estimate the DC resistance, voltage drop and power loss of a rectangular PCB copper trace.

01 / inputs

mm
mm
oz
A
°C

02 / result

RESISTANCE

49.557344 mΩ

Resistance
49.557344 mΩ
Voltage drop
0.049557 V
Power loss
0.049557 W
Cross-section
0.03479 mm²

Calculation trace

  1. 1.7241e-8 × (1 + 0.00393 × (20 − 20)) = 0 Ω·m
    2e-8 Ω·m
    Resistivity at temperature
  2. 1 mm × (1 oz × 34.79 µm) = 0.03479 mm²
    0.03479 mm²
    Cross-section
  3. 0 Ω·m × 0.1 m ÷ 0 m² = 49.557344 mΩ
    49.55734406 mΩ
    Resistance
  4. 1 A × 0.049557 Ω = 0.049557 V
    0.04955734 V
    Voltage drop
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How it works

The trace is treated as a rectangular copper conductor. Cross-section A = width × thickness (thickness comes from the copper weight, 1 oz ≈ 34.79 µm). DC resistance is R = ρ·L / A, where ρ is the resistivity of annealed copper, adjusted for temperature as ρ(T) = ρ₂₀·(1 + α·(T − 20)). Voltage drop is V = I·R and power loss is P = I²·R.

Assumptions & limits

  • Uses the IACS annealed-copper resistivity (ρ₂₀ = 1.7241×10⁻⁸ Ω·m, α = 0.00393/°C); real plating and etch tolerance vary the actual value.
  • DC only — it ignores skin effect at high frequency, plus vias, connectors and pads in series.
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FAQ

Why does a wider or thicker trace have lower resistance?
Resistance is inversely proportional to cross-sectional area (R = ρ·L/A), so more copper — from width or copper weight — lowers it.
Does resistance change with temperature?
Yes. Copper resistance rises roughly 0.393% per °C above 20 °C, so a hot trace drops more voltage and loses more power.
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