How do you calculate PCB trace resistance?

R = ρ(T) × L / (w × t), where ρ(T) is copper resistivity at temperature T (1.724 µΩ·cm at 20 °C, increasing 0.393% per °C), L is trace length, w is width, and t is copper thickness.

What is copper resistivity at different temperatures?

ρ(T) = 1.724 × [1 + 0.00393 × (T − 20)] µΩ·cm. At 25 °C: 1.758, at 60 °C: 1.995, at 100 °C: 2.267 µΩ·cm. This means a trace at 100 °C has 31% more resistance than at 20 °C.

What is an acceptable power loss in a PCB trace?

Power loss P = I²R heats the trace and board. Keep it low enough that the temperature rise stays within IPC limits (typically 10–20 °C above ambient). For small boards or enclosed products, even a few hundred mW can matter.

How does copper weight affect trace performance?

Heavier copper (2 oz, 3 oz) gives a thicker trace with more cross-sectional area. This directly reduces resistance, voltage drop, and power loss — equivalent to doubling the trace width but without using more board space.

What is current density and what is the safe limit?

Current density J = I / (w × t) in A/mm². A common guideline is 20–30 A/mm² for external traces. Higher density causes more heating. IPC-2152 derives width from temperature rise rather than a fixed density limit.

Why does trace length affect performance?

Resistance is directly proportional to length: R = ρL/A. A trace twice as long has twice the resistance, twice the voltage drop, and twice the power loss for the same current.

How do I reduce power loss in a PCB trace?

Widen the trace, use heavier copper, shorten the path, use copper planes instead of thin traces, or reduce the operating current. Each halving of resistance halves the power loss.

What is the cross-sectional area of a 1 oz, 10 mil wide trace?

1 oz copper = 1.378 mil thick. Area = 10 × 1.378 = 13.78 mil² = 0.00889 mm². This is a very narrow trace suitable for low-current signals only.

Should I analyze the return path too?

Yes. Current flows in a loop, so the total drop is the supply trace drop PLUS the return (ground) trace drop. If both paths are similar, total system drop is roughly 2× the single-trace calculation.

PCB Trace Electrical Performance Calculator – Resistance, Voltage Drop & Power Loss

⚙️ Input Panel

📐 Trace Geometry

↔️Width (W)

📊Thickness (T)

📏Length (L)

🌡️ Environmental Factors

🔥Target Temperature

65 °C

❄️Ambient Temperature

25 °C

⚡ System Current

🔌System Current (I)

8.0 A

📊 Results Visualization

Trace Resistance (R)

22.5 mΩ

Voltage Drop (ΔV)

180 mV

✓ within limits

Power Loss (P)

🔥 1.44 W

📈 Voltage Drop vs. Trace Length

📈 Power Loss vs. Current (I)

ℹ️

At 8.0 A through this trace, expect 180 mV drop and 1.44 W of heat. Wider or thicker traces reduce all three. Equations based on the IPC-2152 standard.

⚙️ Calculation Steps

Cross-sectional area: A = W × T (width × copper thickness)

Temperature-adjusted resistivity: ρ(T) = ρ₀ × [1 + α(T − 20)]

Trace resistance: R = ρ × L / A

Voltage drop: ΔV = I × R

Power loss: P = I² × R = I × ΔV

Temp rise from target − ambient: dT = T_target − T_ambient

📊 Live Calculation

Step 1 — Cross-Sectional Area

A = 2.5 × 0.035 = 0.0875 mm²

Step 2 — Trace Resistance

R = ρ × 0.15 / A = 22.5 mΩ

Step 3 — Voltage Drop

ΔV = 8.0 × 0.0225 = 180 mV

Step 4 — Power Loss

P = 8.0² × 0.0225 = 1.44 W

ℹ️

Voltage drop and power loss both scale with current. Keep voltage drop below 3% of supply for best performance, and ensure power dissipation does not overheat the trace. For accurate results, refer to the IPC-2152 standard.

PCB Trace Electrical Performance — Complete Analysis Guide

This PCB trace electrical performance calculator computes the resistance, voltage drop, power loss, current density, and temperature-adjusted copper resistivity for any copper trace given its width, copper weight (thickness), length, current, and operating temperature. A live 3D trace visualization and performance charts update in real time as you adjust parameters, making it easy to see how each variable affects your trace's electrical behavior. Whether you are designing a power distribution network, verifying a critical signal path, or optimizing for thermal performance, this tool provides the numbers and the insight to get it right.

All Formulas at a Glance

Quantity	Formula	Unit
Cross-sectional area	A = w × t_cu	mm²
Resistivity (temp-adj.)	ρ(T) = 1.724 × [1 + 0.00393 × (T − 20)]	µΩ·cm
Resistance	R = ρ(T) × L / A	mΩ
Voltage drop	V_drop = I × R	mV
Power loss	P = I² × R	mW
Current density	J = I / A	A/mm²

Copper Weight vs Performance Impact

Cu Weight	Thickness	Relative R (vs 1 oz)	Effect on Drop & Loss	Cost Impact
0.5 oz	17.5 µm	2.0×	Double the drop and loss	Lowest
1 oz	35 µm	1.0× (baseline)	Standard reference	Standard
2 oz	70 µm	0.5×	Half the drop and loss	+15–25%
3 oz	105 µm	0.33×	One-third of baseline	+30–50%
4 oz	140 µm	0.25×	Quarter of baseline	Specialty

Worked Examples

🔧 Example 1 — 5 V Digital Rail: 2 A, 1 oz, 0.5 mm wide, 80 mm long

GivenI = 2 A, w = 0.5 mm, 1 oz Cu (35 µm), L = 80 mm, T = 40 °C, V_supply = 5 V

Step 1A = 0.5 × 0.035 = 0.0175 mm² | ρ(40) = 1.724 × 1.079 = 1.860 µΩ·cm

Step 2R = 1.860e-6 × 8 / 1.75e-4 = 85.0 mΩ

Step 3V_drop = 2 × 0.085 = 170 mV → 170/5000 = 3.4%

Step 4P = 2² × 0.085 = 340 mW | J = 2 / 0.0175 = 114 A/mm² ⚠️ high!

ResultDrop 3.4% (borderline) | P = 340 mW | J too high — widen to ≥ 1 mm or use 2 oz Cu

⚡ Example 2 — 12 V Motor: 8 A, 2 oz, 3 mm wide, 60 mm long

GivenI = 8 A, w = 3 mm, 2 oz Cu (70 µm), L = 60 mm, T = 50 °C, V_supply = 12 V

Step 1A = 3 × 0.07 = 0.21 mm² | ρ(50) = 1.724 × 1.118 = 1.927 µΩ·cm

Step 2R = 1.927e-6 × 6 / 2.1e-3 = 5.51 mΩ

Step 3V_drop = 8 × 0.00551 = 44.1 mV → 44/12000 = 0.37% ✓

Step 4P = 8² × 0.00551 = 353 mW | J = 8 / 0.21 = 38.1 A/mm² (moderate)

ResultDrop 0.37% (excellent) | P = 353 mW | J acceptable for 2 oz external trace

Performance vs Trace Width — 1 A, 50 mm, 25 °C

Width (mm)	1 oz R (mΩ)	1 oz Drop (mV)	2 oz R (mΩ)	2 oz Drop (mV)
0.15	167	167	83	83
0.25	100	100	50	50
0.5	50	50	25	25
1.0	25	25	12.5	12.5
2.0	12.5	12.5	6.2	6.2
5.0	5.0	5.0	2.5	2.5

Practical Optimization Tips

Doubling width halves R, drop, and loss — the simplest and cheapest optimization.
Upgrading to 2 oz copper has the same effect as doubling width, without using more board space.
Shorten traces by routing power paths directly; every unnecessary millimeter adds resistance.
Use planes for power — a solid copper pour has effectively infinite width and near-zero resistance.
Account for temperature — resistance at 80 °C is 23% higher than at 20 °C; design for operating temperature, not room temperature.
Check return paths — total system drop = supply trace drop + return (ground) trace drop.

Frequently Asked Questions

What's the difference between this calculator and the Voltage Drop calculator?

Both compute R, V_drop, and P, but this tool adds a 3D trace visualization and multi-parameter performance charts that show how resistance, drop, and loss change as you sweep width, length, or current — ideal for trade-off analysis during layout.

How accurate is the temperature compensation?

The linear model ρ(T) = ρ₀ × [1 + α(T−20)] is accurate to within ~1% for −40 °C to +125 °C, which covers virtually all PCB operating ranges.

Should I worry about AC effects (skin effect)?

For DC and low-frequency signals (below ~1 MHz), DC resistance dominates. Above that, skin effect increases effective resistance. This calculator addresses DC/low-frequency performance; for RF traces, use impedance-controlled tools.

Related Calculators

PCB Trace Width Calculator — IPC-2152 minimum width for current and ΔT
Voltage Drop PCB Calculator — focused trace drop and power loss analysis
PCB Via Array & Current Capacity — via resistance and thermal headroom
Ohm's Law Calculator — V = I × R fundamentals