How do you calculate PCB trace width?

Use the IPC-2152 formula: A = (I / (k × ΔT^0.44))^(1/0.725) to find the required cross-sectional area in mil², then divide by copper thickness. k = 0.048 for external layers, 0.024 for internal. The trace width = A / t_cu.

What is the difference between IPC-2152 and IPC-2221?

IPC-2221 uses older, more conservative charts from the 1950s. IPC-2152 (released 2009) is based on modern testing with more variables and generally gives more accurate results. IPC-2152 is the current recommended standard.

What is the difference between internal and external PCB traces?

External traces are on the outer surface and dissipate heat to air, so they can be narrower. Internal traces are buried between layers with less cooling and need roughly twice the cross-sectional area for the same current and ΔT.

What is copper weight and how does it affect trace width?

Copper weight (oz/ft²) defines layer thickness: 1 oz ≈ 35 µm (1.378 mil), 2 oz ≈ 70 µm. Heavier copper provides more cross-section, allowing narrower traces for the same current.

How do I calculate voltage drop in a PCB trace?

V_drop = I × R, where R = ρ × L / (w × t_cu). Copper resistivity ρ ≈ 1.724 µΩ·cm at 20 °C. For long or high-current traces, voltage drop may be the limiting factor rather than temperature rise.

What is a safe current density for PCB traces?

A common guideline is 20–30 A/mm² for external traces. IPC-2152 doesn't specify a fixed density limit — it calculates width from current and temperature rise. Check both temperature and voltage drop.

Why should I use a safety factor?

Real boards have vias, connectors, nearby heat sources, manufacturing tolerances, and restricted airflow that reduce capacity. A safety factor of 1.2–1.5 compensates for these and improves long-term reliability.

Does trace length affect the required width?

For steady-state heating, the IPC formula depends on current and ΔT, not length. However, longer traces have higher resistance and voltage drop, which may require a wider trace to keep the drop acceptable.

PCB Trace Width Calculator – IPC-2152 Current Capacity, Width & Voltage Drop

🔲 PCB Trace Width Calculator

Calculate the required PCB trace width for a given current, copper weight, temperature rise and more.

Units:

Input Settings

⚡

Current (I)

The current flowing in the trace

▦

Copper Weight

Copper thickness

🌡

Temperature Rise (ΔT)

Allowable temperature rise above ambient

°C

🌡

Ambient Temperature (Ta)

Ambient temperature

°C

▤

Board Thickness

Total board thickness

📏

Trace Length (Optional)

For voltage drop calculation

∿

Voltage Drop (Optional)

Maximum allowed voltage drop

▢

Conductor

External / Internal Layer

🛡

Safety Factor

Additional margin

Results

Required Trace Width (w)

1.06 mm (41.9 mil)

The minimum trace width required to carry 2.00 A with a temperature rise of 10 °C

Current Density (J) ⓘ

53.75 A/mm²

Temperature Rise

10.0 °C

Voltage Drop (Approx.) ⓘ

0.045 V

Resistance

22.6 mΩ

Recommended Trace Widths (By Current)

Current (A)	Trace Width (mm)
Current (A)	0.5 oz (18 µm)	1 oz (35 µm)	2 oz (70 µm)	3 oz (105 µm)

Values are approximate. IPC-2152 external layer, ΔT = 10 °C, Ta = 25 °C.

Visualization

IPC-2152 Standard

This calculator uses the IPC-2152 standard for external layers.

Notes & Quick Reference

• Results are based on IPC-2152 formulas.
• Actual temperature may vary based on layout, airflow, and surrounding copper.
• Use larger width for high reliability designs.

⏱

Lower ΔT

Wider trace

🌡

Higher Temp Rise

Narrower trace

⚡

Higher Current

Wider trace

📏

Longer Length

More voltage drop

▦

More Copper (oz)

Narrower trace

▤

Internal Layer

Wider than external

Formula (IPC-2152)External Layer

A = Ik × (ΔT)^0.44^{1 / 0.725} | w = A / (t_cu)

I = Current (A), ΔT = Temp. Rise (°C)
k = 0.048 (external) / 0.024 (internal)
A = Cross-section, t_cu = Copper thickness, w = Width

PCB Trace Width Calculator — Complete IPC-2152 Guide

This PCB trace width calculator uses the industry-standard IPC-2152 method to determine the minimum copper trace width needed to carry a given current while keeping temperature rise within a safe limit. It also computes current density, trace resistance, and voltage drop — the three quantities every PCB designer must check when laying out power traces. Whether you are routing 0.5 A to an IC or 30 A through a motor driver, this tool gives you the exact width in mm and mils with a single click.

IPC-2152 Trace Width Formula

A = ( I / ( k × ΔT^0.44 ) )^{1 / 0.725}

w = A / t_cu

Where:
• A = required cross-sectional area (mil²)
• I = current (A), including safety factor
• ΔT = allowable temperature rise (°C)
• k = 0.048 (external) or 0.024 (internal layers)
• t_cu = copper thickness (1 oz ≈ 1.378 mil ≈ 35 µm)
• w = minimum trace width (mil)

Copper Weight / Thickness Reference

Copper Weight	Thickness (µm)	Thickness (mil)	Typical Use
0.5 oz	17.5	0.689	Fine-pitch signal layers
1 oz	35	1.378	Standard — most PCBs
2 oz	70	2.756	Power distribution, high-current
3 oz	105	4.134	Heavy power, motor drives
4 oz	140	5.512	Busbar-style power planes
6 oz	210	8.268	Extreme current applications

Trace Width vs Current — Quick Reference (External, ΔT = 10 °C)

Current (A)	1 oz Width (mm)	1 oz Width (mil)	2 oz Width (mm)	2 oz Width (mil)
0.5	0.18	7	0.09	3.5
1.0	0.42	17	0.21	8
2.0	1.07	42	0.53	21
3.0	1.87	74	0.94	37
5.0	3.93	155	1.97	78
10.0	10.2	402	5.1	201
20.0	26.6	1048	13.3	524

Worked Examples

🔧 Example 1 — 2 A External Trace, 1 oz Copper, ΔT = 10 °C

GivenI = 2 A, Safety factor = 1.25, k = 0.048 (external), ΔT = 10 °C, 1 oz Cu (35 µm = 1.378 mil)

Step 1Effective current: I_eff = 2 × 1.25 = 2.5 A

Step 2Area: A = (2.5 / (0.048 × 10^0.44))^(1/0.725) ≈ 47 mil²

Step 3Width: w = 47 / 1.378 ≈ 34 mil ≈ 0.87 mm

ResultMinimum trace width ≈ 0.87 mm (34 mil) for 2 A with 25% safety margin

⚡ Example 2 — 10 A Internal Trace, 2 oz Copper, ΔT = 20 °C

GivenI = 10 A, k = 0.024 (internal), ΔT = 20 °C, 2 oz Cu (70 µm = 2.756 mil), L = 50 mm

Step 1Area: A = (10 / (0.024 × 20^0.44))^(1/0.725) ≈ 455 mil²

Step 2Width: w = 455 / 2.756 ≈ 165 mil ≈ 4.2 mm

Step 3R = 1.724µΩ·cm × 5cm / (0.42cm × 0.007cm) ≈ 29.3 mΩ | V_drop = 10 × 0.029 ≈ 293 mV

ResultWidth ≈ 4.2 mm (165 mil) | Voltage drop ≈ 293 mV over 50 mm — check if acceptable

Internal vs External Layer Comparison

Property	External Layer	Internal Layer
IPC constant (k)	0.048	0.024
Heat dissipation	Good — exposed to air	Poor — sandwiched in FR4
Required width for same I & ΔT	Narrower	~2× wider
Use case	Component-side power traces	Power planes, inner routing
Typical ΔT target	10–20 °C	10–20 °C (more conservative)

Voltage Drop and Resistance

Resistance: R = ρ × L / (w × t_cu)
Voltage Drop: V_drop = I × R
Power Loss: P = I² × R

ρ_copper ≈ 1.724 µΩ·cm at 20 °C (increases ~0.39% per °C)

For long traces or high currents, voltage drop can limit performance more than temperature rise. Always check both. A 5 V supply with 250 mV of trace drop delivers only 4.75 V to the load — a 5% loss that can cause regulators or digital ICs to operate outside spec.

Practical Design Tips

Size power traces generously — a failure in a power path is costly; adding an extra 20–30% width costs nothing.
Use copper pours and planes — large polygons spread current and heat far better than thin traces.
Check the bottlenecks — vias, pads, and connector necks are the narrowest points in the path.
Use 2 oz copper for power boards — it halves the required width at no routing cost.
Account for temperature — copper resistivity rises ~0.39%/°C; a trace at 80 °C has ~23% more resistance than at 20 °C.
Always apply a safety factor (1.2–1.5) — IPC formulas assume ideal conditions; real boards have vias, connectors, and restricted airflow.

Frequently Asked Questions

What temperature rise should I use?

10 °C is a common conservative target. 20 °C is moderate and widely used. 30–40 °C may be acceptable for non-critical traces. Lower ΔT = wider, cooler traces.

Does trace length affect required width?

Not for thermal sizing (the IPC formula depends only on I and ΔT). But length affects resistance and voltage drop, which may require a wider trace.

Is the IPC-2152 result exact?

It is a well-established engineering estimate. Actual performance depends on layout, adjacent copper, airflow, and ambient conditions. Always add margin.

When should I use 2 oz or 3 oz copper?

When carrying more than ~5 A continuously, when board space is limited and you can't make traces wider, or for any power-dense design like motor drives or LED arrays.

What is current density and what's safe?

Current density (J = I / A) is typically kept below 20–30 A/mm² for external traces. Higher densities cause more heating. IPC-2152 doesn't set a fixed density limit — it derives width from ΔT instead.

Related Calculators

Voltage Drop PCB Calculator — trace resistance, voltage drop, and power loss
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