How do you calculate voltage drop in a PCB trace?

First calculate trace resistance: R = ρ × L / (w × t), where ρ is copper resistivity (~1.724 µΩ·cm at 20 °C), L is length, w is width, and t is copper thickness. Then V_drop = I × R.

What is an acceptable voltage drop in PCB traces?

For critical circuits (precision analog, power supplies, high-speed digital), keep drop below 3% of supply voltage. For general circuits, 3–5% is acceptable. Above 5% is not recommended.

How does temperature affect PCB trace resistance?

Copper resistivity increases ~0.39% per °C. At 80 °C a trace has about 23% more resistance than at 20 °C. Use ρ(T) = 1.724 × [1 + 0.00393 × (T − 20)] µΩ·cm.

What is the resistivity of copper used in PCBs?

PCB copper (electrodeposited) has a resistivity of approximately 1.724 µΩ·cm (1.724 × 10⁻⁶ Ω·cm) at 20 °C, with a temperature coefficient α = 0.00393 /°C.

How do I reduce voltage drop in a PCB trace?

Make the trace wider, use heavier copper (2 oz or 3 oz), shorten the trace path, use copper pours or planes instead of thin traces, and add parallel vias to reduce resistance at layer transitions.

Does trace width affect voltage drop?

Yes — directly. A wider trace has more cross-sectional area, lower resistance, and therefore lower voltage drop for the same current and length.

What is power loss in a PCB trace?

Power loss P = I² × R = I × V_drop. This power is dissipated as heat in the copper, raising the trace temperature. High power loss can degrade the board and affect nearby components.

How do I calculate current density in a PCB trace?

Current density J = I / A, where A = width × thickness. A common guideline is to keep J below 20–30 A/mm² for external traces to avoid excessive heating.

What is IPC-2152 and how does it relate to voltage drop?

IPC-2152 is an industry standard for PCB trace sizing based on current and temperature rise. While it primarily addresses thermal capacity, it also provides the basis for resistance and voltage drop calculations using the trace geometry it recommends.

Voltage Drop PCB Calculator – Trace Resistance, Power Loss & IPC-2152 Check

R = ρ × L / A

Trace Resistance Formula

V_drop = I × R

Voltage Drop Formula

⚡ DC Current (I)

0.1 A 50 A

📏 Trace Length (L)

1 mm 500 mm

⬜ Trace Width (W)

0.1 mm 25 mm

📊 Copper Thickness (t)

0.1 oz 3 oz

🔲 PCB Layer

🌡️ Temperature

°C

-40 °C 125 °C

Ω Copper Resistivity (ρ)

µΩ·cm

Default: 1.724 µΩ·cm @ 20°C

📋 TOP VIEW (Trace on PCB)

🔍 CROSS SECTION

ℹ️

Voltage drop = 0.0689V (3.45%)

Voltage Drop (V)

0.0689

Voltage Drop (%)

3.45

Trace Resistance (R)

0.0344

Power Loss (P)

137.8

Current Density (J)

1.27

Resistivity @ Temp

1.750

⚠️ Guidelines

< 3%

Excellent

3% - 5%

Acceptable

> 5%

Not Recommended

Voltage Drop PCB Calculator — Complete Guide to Trace Resistance & Power Loss

This voltage drop PCB calculator computes the resistance, voltage drop (V = I × R), power loss (P = I²R), and current density for any copper PCB trace given its width, thickness (copper weight), length, current, and operating temperature. It also checks your trace against IPC-2152 guidelines and flags whether the drop is within the recommended 3% or 5% limits for your supply voltage. Whether you are designing a power distribution network, routing motor drivers, or optimizing a battery-powered board, this tool shows exactly how much voltage you lose in the copper before it reaches the load.

Core Formulas

Trace Resistance: R = ρ(T) × L / A

Voltage Drop: V_drop = I × R

Power Loss: P = I² × R = I × V_drop

Current Density: J = I / A

Temperature-adjusted resistivity:
ρ(T) = 1.724 µΩ·cm × [1 + 0.00393 × (T − 20 °C)]

A = cross-sectional area = width × thickness

Recommended Voltage Drop Limits

Category	Max Drop (%)	Typical Applications
Critical (< 1%)	< 1%	Precision ADC references, voltage regulators, RF LNA bias
Sensitive (< 3%)	< 3%	Digital IC power rails, high-speed FPGA cores, USB supplies
General (3–5%)	3–5%	Standard logic, LED drivers, motor control
Non-critical (> 5%)	> 5%	Not recommended — regulation and reliability degrade

Copper Resistivity at Temperature

Temperature (°C)	ρ (µΩ·cm)	Increase vs 20 °C
20 (reference)	1.724	0%
25	1.758	+2.0%
40	1.860	+7.9%
60	1.995	+15.7%
80	2.131	+23.6%
100	2.267	+31.5%
125	2.436	+41.3%

Worked Examples

🔧 Example 1 — 3.3 V Rail, 1 A, 50 mm Trace, 1 oz Cu, 0.3 mm Wide

GivenV_supply = 3.3 V, I = 1 A, L = 50 mm, w = 0.3 mm, 1 oz Cu (35 µm), T = 40 °C

Step 1ρ(40) = 1.724 × [1 + 0.00393 × 20] = 1.724 × 1.0786 = 1.860 µΩ·cm

Step 2A = 0.03 cm × 0.0035 cm = 1.05×10⁻⁴ cm²

Step 3R = 1.860×10⁻⁶ × 5 / 1.05×10⁻⁴ = 88.6 mΩ

Step 4V_drop = 1 × 0.0886 = 88.6 mV → 88.6/3300 = 2.7% ✓ (within 3%)

Step 5P_loss = 1² × 0.0886 = 88.6 mW

ResultV_drop = 88.6 mV (2.7%) | R = 88.6 mΩ | P = 88.6 mW — acceptable for general circuits

⚡ Example 2 — 12 V Motor Rail, 5 A, 100 mm Trace, 2 oz Cu, 2 mm Wide

GivenV_supply = 12 V, I = 5 A, L = 100 mm, w = 2 mm, 2 oz Cu (70 µm), T = 60 °C

Step 1ρ(60) = 1.724 × [1 + 0.00393 × 40] = 1.724 × 1.1572 = 1.995 µΩ·cm

Step 2A = 0.2 cm × 0.007 cm = 1.4×10⁻³ cm²

Step 3R = 1.995×10⁻⁶ × 10 / 1.4×10⁻³ = 14.25 mΩ

Step 4V_drop = 5 × 0.01425 = 71.3 mV → 71.3/12000 = 0.59% ✓ (excellent)

Step 5P_loss = 5² × 0.01425 = 356 mW

ResultV_drop = 71.3 mV (0.59%) | R = 14.25 mΩ | P = 356 mW — well within limits

Voltage Drop Quick Reference — 1 A, 50 mm Length, T = 25 °C

Trace Width (mm)	1 oz (35 µm) Drop	2 oz (70 µm) Drop	3 oz (105 µm) Drop
0.1	251 mV	125 mV	84 mV
0.25	100 mV	50 mV	33 mV
0.5	50 mV	25 mV	17 mV
1.0	25 mV	13 mV	8 mV
2.0	13 mV	6 mV	4 mV
5.0	5 mV	3 mV	2 mV

How to Reduce Voltage Drop

Widen the trace — doubling width halves resistance and drop.
Use heavier copper — 2 oz gives the same area as a trace twice as wide on 1 oz.
Shorten the path — direct routing is always better; avoid unnecessary bends.
Use copper pours / planes — massive cross-section, negligible resistance.
Multiple vias — reduce resistance at layer transitions where traces change sides.
Lower operating temperature — copper resistivity rises ~0.39% per °C; better cooling means less drop.

Practical Applications

Power Distribution Networks (PDN)

Voltage regulators deliver a specified output, but the trace connecting them to the load adds resistance. If a 3.3 V regulator feeds an IC through a 100 mV drop, the IC sees only 3.2 V — below tolerance for many parts. Check every power trace from source to load.

LED Constant-Current Drivers

LED strings are often distributed across a board. Even small drops along the power trace cause brightness variation between LEDs near the driver and those far away. Wide traces or planes equalize delivery.

Battery-Powered Devices

Every millivolt lost in a trace is a millivolt the battery can't deliver to the load. In a 3.0 V coin-cell circuit, 100 mV of trace drop is 3.3% — significant for low-voltage regulators with narrow dropout margins.

Frequently Asked Questions

What is the formula for PCB trace voltage drop?

V_drop = I × R, where R = ρ(T) × L / (w × t). At 20 °C, copper ρ = 1.724 µΩ·cm. Adjust for temperature with α = 0.00393 /°C.

Does trace length matter?

Directly — resistance is proportional to length. A 100 mm trace has exactly twice the resistance (and voltage drop) of a 50 mm trace with the same width and thickness.

Should I calculate voltage drop for signal traces too?

Usually not — signal currents are tiny so the drop is negligible. Focus on power traces, ground returns, and any path carrying more than ~100 mA.

How accurate is this calculator?

It applies standard copper resistivity formulas and temperature compensation. Real-world results depend on actual copper thickness (manufacturing tolerance ±10%), trace roughness, and ambient conditions. Always add margin.

What about return-path drop?

Current flows in a loop. The voltage delivered to the load equals V_supply minus the drop in the supply trace AND the return (ground) trace. If both traces are the same, the total drop is twice what this calculator shows for one trace.

Related Calculators

PCB Trace Width Calculator — IPC-2152 minimum width for a given current and temperature rise
Trace Electrical Performance — resistance, drop, and loss with 3D visualization
PCB Via Array & Current Capacity — via resistance and thermal headroom
Ohm's Law Calculator — V = I × R fundamentals