PCB Trace Width Calculator
Calculate the minimum PCB trace width for a given current using the IPC-2221 standard. Enter amps, temperature rise, copper weight and layer for an instant result.
Updated 2026-06-14 · Free · No sign-up · Runs privately in your browser
Show the formula & steps
IPC-2221 estimate for currents up to 35 A, widths up to 400 mils and temperature rise up to 100°C. Add margin for vias, high-frequency and safety-critical designs.
How the PCB Trace Width Calculator Works
This calculator finds the minimum copper trace width a printed circuit board needs to safely carry a given current without overheating. It uses the IPC-2221 standard, the long-established industry guideline for conductor sizing. Enter the current, the allowable temperature rise, the copper weight and whether the trace runs on an external or internal layer, and it returns the width in mils and millimetres along with the required cross-sectional area.
The Formula
IPC-2221 first calculates the cross-sectional area of copper needed (in square mils):
A (mil²) = ( I / (k × ΔT^0.44) )^(1/0.725)
where:
- I = current in amps
- ΔT = allowable temperature rise above ambient, in °C
- k = 0.048 for external (outer) layers, 0.024 for internal layers
The exponents 0.44 and 0.725 come from curve-fitting the original IPC charts. Once you have the area, convert it to a width by dividing by the copper thickness:
Thickness (mils) = copper weight (oz) × 1.378 Width (mils) = A ÷ thickness
To convert mils to millimetres, multiply by 0.0254 (1 mil = 0.0254 mm).
Worked Example
For 2 A, a 10°C temperature rise, 1 oz copper, on an external layer:
- Area = (2 / (0.048 × 10^0.44))^(1/0.725) = 42.4 mil²
- Thickness = 1 × 1.378 = 1.378 mils
- Width = 42.4 ÷ 1.378 = ≈ 30.8 mils (0.78 mm)
So a roughly 31-mil trace safely carries 2 A with only a 10°C rise on a standard 1 oz external layer.
Why Trace Width Matters
A trace that is too narrow for its current heats up, increasing resistance and risking delamination or open circuits. Sizing copper correctly lets you:
- Limit heating — keep the temperature rise within your chosen budget (10°C is common).
- Reduce voltage drop — wider traces have lower resistance and lose less energy.
- Save board space — using the right copper weight avoids over-sizing every track.
| Current | ΔT 10°C, 1 oz external | Approx. width |
|---|---|---|
| 1 A | external layer | ≈ 12 mils (0.30 mm) |
| 2 A | external layer | ≈ 31 mils (0.78 mm) |
| 5 A | external layer | ≈ 110 mils (2.8 mm) |
Remember IPC-2221 is intentionally conservative and ignores nearby copper planes and board material. For demanding designs, cross-check against IPC-2152 and validate with real thermal measurements.
Frequently asked questions
How do I calculate PCB trace width for a given current?+
Use the IPC-2221 formula. First find the cross-sectional area in square mils: A = (I / (k × ΔT^0.44))^(1/0.725), where k is 0.048 for external layers and 0.024 for internal layers. Then divide the area by the copper thickness in mils (copper weight in oz × 1.378) to get the trace width in mils.
What trace width do I need for 1 amp?+
For 1 A with a 10°C temperature rise on a 1 oz external layer, IPC-2221 gives a minimum width of about 12 mils (0.30 mm). The exact value depends on your temperature rise, copper weight and whether the trace is on an external or internal layer.
Why are internal traces wider than external traces?+
Internal traces are buried between dielectric layers and dissipate heat much more poorly than external traces exposed to air. IPC-2221 uses k = 0.024 for internal layers versus 0.048 for external, which roughly doubles the required cross-sectional area and therefore the width for the same current.
What does copper weight mean in this calculator?+
Copper weight is the thickness of the copper foil, given in ounces per square foot. One ounce of copper spreads to about 1.378 mils (35 microns) thick. Heavier copper (2 oz, 3 oz) is thicker, so it carries the same current with a narrower trace.
Is the IPC-2221 trace width formula accurate for high current?+
IPC-2221 is a conservative design guideline derived from charts valid for currents up to about 35 A, widths up to 400 mils and temperature rise up to 100°C. For very high current, RF, or safety-critical boards, add margin, consider IPC-2152 (which accounts for board material and copper planes), and verify with thermal testing.