PCB Trace Width Calculator
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.
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
In Flux
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.
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.
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.
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
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.
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.
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.
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.
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.
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.