# PCB Trace Width Calculator

Free IPC-2221 PCB trace width calculator. Pick an external or internal conductor, enter current, temperature rise and copper thickness in your own units, and get the minimum trace width plus cross-section, resistance, voltage drop and power loss.

Size your copper for current in seconds. Pick **external or internal** copper, enter your current, allowed temperature rise and copper thickness, and get the **minimum trace width** plus cross-section, resistance, voltage drop and power loss. Based on the **IPC-2221** conductor-sizing charts.

Board view

Results

Minimum trace width —

Cross-section area —

Resistance —

Voltage drop —

Power loss —

IPC-2221 sizes copper for current-carrying capacity only. Add margin for vias, connectors and thermal hotspots, and check the resistance and voltage drop before you commit — resistance uses copper resistivity at the trace's operating temperature (ambient + rise).

## Stop typing trace widths by hand

A calculator is a sanity check — but you still have to copy the number into a constraint dialog for every net, on every layer, and redo it when the copper weight changes. In Flux, you just ask. Tell Flux how much current a net carries and it sizes the copper, sets the net class and routes it — live on the canvas.

-   Set current per net, not width per trace
-   Flux applies the width and routes the net for you
-   Widths stay IPC-compliant across copper weights and inner layers

[Try Flux for Free](https://www.flux.ai/signup)

### In Flux

VBAT\_5V carries 3 A on the top layer — how wide should it be, and can you route it?

![Flux](https://www.flux.ai/p/assets/site/6446c14683b3da60aea75bce_copilot-icon-filled-white.svg)

For 3 A on 1 oz external copper with a 10 °C rise, IPC-2221 needs:

-   **Width:** 1.37 mm (54 mil)
-   **Drop over 50 mm:** 57 mV

I've set the **VBAT\_5V** net class to 1.4 mm and routed it on the top layer. If it has to drop to an inner layer I'll widen it to 3.6 mm.

## How the trace width is calculated

The IPC-2221 conductor-sizing formula, evaluated client-side as you type.

01

### Required copper area

Area in mils². The constant k is 0.048 for external conductors and 0.024 for internal ones, because buried copper cannot shed heat into the air.

02

### Copper thickness

One ounce of copper per square foot is about 35 µm (1.378 mil) thick. Enter a thickness directly if your fab quotes microns or mils.

03

### Width, resistance & drop

Divide the area by the thickness to get the width. Resistance, voltage drop and power loss then follow from the trace length and copper resistivity at ambient + rise.

## Trace width calculator FAQ

### How do you calculate PCB trace width?

Trace width for current capacity uses the IPC-2221 formula. First find the required copper cross-sectional area **A = (I / (k · ΔT0.44))1/0.725**, where *I* is current in amps, *ΔT* is the allowed temperature rise, and *k* is 0.048 for external layers or 0.024 for internal layers. Divide that area by the copper thickness (1 oz ≈ 35 µm, or 1.378 mils) to get the width. This calculator does all of that for you as you type.

### What is the difference between an external and an internal trace?

An external trace runs on an outer copper layer, so it sheds heat into the surrounding air and IPC-2221 allows a higher current density (k = 0.048). An internal trace is buried between dielectric layers, where the heat is trapped in the laminate, so the standard halves the constant (k = 0.024) — halving k raises the required area by 21/0.725, so an internal trace ends up roughly 2.6× as wide as an external one for the same current and temperature rise. Switch the conductor location above to see both.

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

IPC-2221 is the classic, conservative chart-based method that most online calculators (and this one) use. IPC-2152 is the newer standard built on modern thermal testing — it factors in board thermal conductivity, adjacent copper planes, and environment, and usually permits narrower traces. IPC-2221 is a safe, widely accepted starting point; step up to IPC-2152 when you need to optimize board area.

### How wide should a trace be for 1 A, 3 A, or 5 A?

On 1 oz external copper with a 10 °C rise: ~1 A needs ≈0.30 mm (12 mils), ~3 A needs ≈1.37 mm (54 mils), and ~5 A needs ≈2.77 mm (109 mils). Internal layers need about 2.6× these widths. Enter your exact values above to get precise numbers.

### Does copper weight matter?

Yes. Heavier copper (2 oz, 3 oz) is thicker, so it carries more current at the same width — or lets you use a narrower trace for the same current. Standard PCBs use 1 oz (35 µm). Power boards often specify 2 oz or more. You can also enter the finished thickness your fab quotes directly, in µm, mils or mm.

### Do I have to type trace-width constraints manually in Flux?

No. That's the whole point. Assign a target current to a net in Flux and the cloud-native routing engine calculates and applies the IPC-compliant trace width dynamically on the canvas — no manual constraint entry, no back-and-forth with a spreadsheet.

## Design the whole board with AI

From schematic to IPC-compliant copper — let Flux size and route your traces.

[Try Flux for Free](https://www.flux.ai/signup)