Tools / PCB trace width calculator
PCB trace width calculator
Find the trace width for a given current, the current a trace can carry or how hot it will run. IPC-2221 inner and outer layers and IPC-2152 side by side, with resistance, voltage drop and power loss.
Pick what to solve for and enter your numbers. Results update as you type, and the most conservative result for your inputs is tagged.
IPC-2221 Internal layer
Most conservative
Required width
–
- Cross-section
- Resistance
- Voltage drop
- Power loss
- Trace temperature
Inner-layer trace. Also use it for outer layers that are potted, thickly coated or in a vacuum.
IPC-2221 External layer
Most conservative
Required width
–
- Cross-section
- Resistance
- Voltage drop
- Power loss
- Trace temperature
Outer-layer trace in still air. IPC-2152 testing found these curves optimistic above a few amps.
IPC-2152 Any layer
Most conservative
Required width
–
- Cross-section
- Resistance
- Voltage drop
- Power loss
- Trace temperature
Universal chart for a board with no copper plane nearby. A plane close to the trace lowers the rise.
How the calculator works
Both IPC standards relate three things: the current, the temperature rise you can accept and the cross-sectional area of the copper.
The calculator finds the copper area each standard needs for your current and allowed rise, then divides by the copper thickness to get a width. Solving for current or temperature rise runs the same relationship the other way.
IPC-2221
The older curves, carried over from decades-old test data. They split traces into internal and external, and give internal traces roughly half the current of external ones.
I = k × ΔT0.44 × A0.725
k = 0.048 for external layers and 0.024 for internal layers, with I in amps, ΔT in °C and A in square mils. The charts cover up to 35 A, 400 mil wide traces, 10 to 100 °C of rise and 0.5 to 3 oz copper.
IPC-2152
Published in 2009 from new testing. Its universal chart covers a trace on a board with no copper plane nearby, and it applies to inner and outer layers alike. We use a published curve fit of that chart, which tracks it within about 3%:
A = (117.555 × ΔT−0.913 + 1.15) × I(0.84 × ΔT−0.108 + 1.159)
The full standard adds modifiers for copper thickness, board thickness, plane distance and laminate. A solid plane close to the trace usually lowers the real rise well below the universal chart, so treat this result as the no-plane baseline. Above a few amps it asks for more copper than the IPC-2221 external curve, which IPC-2152 testing found optimistic.
Resistance, voltage drop and power loss
R = ρ × L / A × (1 + 0.00393 × (T − 20 °C))
ρ is the resistivity of copper, 1.72 × 10−8 Ω·m, L is the trace length and T is the trace temperature: ambient plus the rise. Voltage drop is I × R and power loss is I² × R.
These results are estimates from curve fits to the IPC charts. They do not account for nearby heat sources, parallel traces closer than about an inch, vias, airflow or the enclosure. Use them for early sizing, and confirm high-current or high-reliability designs with thermal analysis or measurement.
Trace width vs current for 1 oz copper
Required widths for common currents, from the same formulas. At 2 oz copper each width halves, because the required copper area stays the same.
10 °C temperature rise
| Current | IPC-2221 external | IPC-2221 internal | IPC-2152 |
|---|---|---|---|
| 0.25 A | 1.75 mil (0.044 mm) | 4.55 mil (0.115 mm) | 0.91 mil (0.023 mm) |
| 0.5 A | 4.55 mil (0.115 mm) | 11.8 mil (0.30 mm) | 3.2 mil (0.081 mm) |
| 1 A | 11.8 mil (0.30 mm) | 30.8 mil (0.78 mm) | 11.3 mil (0.29 mm) |
| 2 A | 30.8 mil (0.78 mm) | 80 mil (2.03 mm) | 39.6 mil (1.01 mm) |
| 3 A | 53.8 mil (1.37 mm) | 140 mil (3.56 mm) | 82.6 mil (2.10 mm) |
| 5 A | 109 mil (2.77 mm) | 283 mil (7.19 mm) | 209 mil (5.30 mm) |
| 7.5 A | 190 mil (4.84 mm) | 495 mil (12.6 mm) | 435 mil (11.1 mm) |
| 10 A | 283 mil (7.19 mm) | 737 mil (18.7 mm) | 734 mil (18.6 mm) |
20 °C temperature rise
| Current | IPC-2221 external | IPC-2221 internal | IPC-2152 |
|---|---|---|---|
| 0.25 A | 1.15 mil (0.029 mm) | 2.98 mil (0.076 mm) | 0.55 mil (0.014 mm) |
| 0.5 A | 2.98 mil (0.076 mm) | 7.77 mil (0.197 mm) | 1.87 mil (0.048 mm) |
| 1 A | 7.77 mil (0.197 mm) | 20.2 mil (0.51 mm) | 6.37 mil (0.162 mm) |
| 2 A | 20.2 mil (0.51 mm) | 52.6 mil (1.33 mm) | 21.7 mil (0.55 mm) |
| 3 A | 35.3 mil (0.90 mm) | 91.9 mil (2.34 mm) | 44.4 mil (1.13 mm) |
| 5 A | 71.5 mil (1.82 mm) | 186 mil (4.72 mm) | 109 mil (2.78 mm) |
| 7.5 A | 125 mil (3.18 mm) | 325 mil (8.26 mm) | 224 mil (5.69 mm) |
| 10 A | 186 mil (4.72 mm) | 484 mil (12.3 mm) | 372 mil (9.46 mm) |
Widths above 400 mil are beyond the IPC-2221 charts and are extrapolated. IPC-2152 values assume no copper plane near the trace.
Common questions
What temperature rise should I use?
10 °C is a safe default for almost any board. 20 to 30 °C is common where space is tight, as long as the laminate, nearby parts and the enclosure can take the heat. Add the rise to the highest ambient the product will see, not room temperature.
Which result should I design to?
Without data on your stackup, use the result tagged Most conservative. On multilayer boards with a solid plane close to the trace, the IPC-2152 result is a reasonable baseline and the real rise is usually lower. Potted, thickly coated or vacuum assemblies should use IPC-2221 internal values for every layer.
Why does IPC-2221 make internal traces wider than external ones?
Under IPC-2221, outer traces shed heat to the air while inner traces are wrapped in laminate, so its curves give inner traces about half the current. IPC-2152 testing found that laminate conducts heat better than assumed, which is why it uses one chart for every layer.
What copper thickness should I enter?
Enter the finished copper. 1 oz is about 35 µm (1.38 mil). Outer layers often start as 0.5 oz foil and are plated up to roughly 1 to 1.5 oz, so check the finished thickness with your fabricator. Thicker copper carries the same current in a narrower trace.
Does it work for pulsed or AC current?
Use the RMS current, as long as the pulses are short compared with how fast the trace heats up, which is on the order of seconds. For long pulses, size the trace for the peak current.
What about very high currents or wide traces?
Both standards stop at their test limits: about 35 A and 400 mil for IPC-2221, and about 30 A for IPC-2152. Beyond that the formulas extrapolate, and the calculator warns you. High-current paths are usually better as pours, planes or bus bars, checked with thermal simulation or measurement.
Do short neck-downs and thermal relief spokes need the full width?
No. The standards assume long, isolated traces. A short neck into a pad or the spokes of a thermal relief are heat-sunk at both ends and can be narrower than the calculator suggests, though they should stay as wide as assembly allows.
Can Evertech review my power layout?
Yes. Current capacity, stackup and copper weight are part of every PCB layout and DFM review we do, and our production team builds the boards here in Cedarburg. Send your files for a quote.
Sizing a high-current board?
Our engineers lay out power paths, stackups and copper weights alongside our own production team in Cedarburg, Wisconsin. Send your files and we will take a look.