PCB Trace Width Calculator
Compare the familiar legacy trace-current relationship with a published approximation based on IPC-2152 data. Solve width, current or temperature rise within stated model limits. IPC-2221C is actively revised; IPC currently marks IPC-2152 as “No Longer Maintained”, so neither row should be treated as an automatic present-day acceptance criterion.
| Basis | Min width | Cross-section | Resistance | V-drop | Power |
|---|---|---|---|---|---|
| IPC-2221 external | - | - | - | - | - |
| IPC-2221 internal | - | - | - | - | - |
| IPC-2152 | - | - | - | - | - |
Method based on Legacy IPC-2221 relationship; published IPC-2152 reference fit · editorial check September 2026 · revision 1.1
Trace width, thickness and copper area
How it's calculated
IPC-2221 links a conductor's cross-sectional area to the current it carries and the temperature rise that current produces. One equation ties the three together:
- I
- current, in amperes
- ΔT
- temperature rise above ambient, in °C
- A
- cross-sectional area, in mil²
- k
- 0.048 for external layers, 0.024 for internal
The mode switch rearranges the legacy relationship to solve width, current or temperature rise. Width equals cross-sectional area divided by copper thickness. Resistance uses R = ρL/A at an assumed ambient of 25 °C plus the calculated rise. The separate IPC-2152 row uses the cited published reference fit, with its own validity checks. It does not implement all chart corrections for a particular board.
2 A on an external 1 oz trace, 10 C rise
- Required cross-section A = (I / (k x dT^0.44))^(1/0.725), with k = 0.048 for an external layer.
- A = (2 / (0.048 x 10^0.44))^(1/0.725) = 42.4 mil-squared.
- Width = area / copper thickness. A 1 oz layer is 1.378 mil thick, so width = 42.4 / 1.378 = 30.8 mil (0.78 mm).
- This is the legacy equation’s estimate, not a certified minimum. Account for manufacturing tolerances and validate the thermal behavior of the completed board.
5 A on an internal 2 oz trace, 10 C rise
- Internal layers use k = 0.024, half the external value, because the 1950s IPC-2221 model assumes they shed heat less easily.
- A = (5 / (0.024 x 10^0.44))^(1/0.725) = 390 mil-squared.
- 2 oz copper is 2.756 mil thick, so width = 390 / 2.756 = 142 mil (3.6 mm).
- This width follows from the legacy internal coefficient. A board-specific thermal assessment can produce a different answer.
Same 2 A trace, but allow a 20 C rise
- Raising the allowed temperature rise lets the trace run hotter, so it can be narrower.
- A = (2 / (0.048 x 20^0.44))^(1/0.725) = 27.8 mil-squared.
- Width = 27.8 / 1.378 = 20.2 mil (0.51 mm), down from 30.8 mil at a 10 C rise.
- Trading temperature headroom for board space is a real design lever, but a hotter trace also has higher resistance and sits closer to its limit.
Quick reference
Minimum width at a 10 °C rise on 1 oz copper, by current. Treat it as a starting point, then confirm with your own copper weight and temperature rise above.
| Current | External | Internal |
|---|---|---|
| 0.5 A | 4.5 mil | 11.8 mil |
| 1 A | 11.8 mil | 30.8 mil |
| 2 A | 30.8 mil | 80.0 mil |
| 3 A | 53.8 mil | 140 mil |
| 5 A | 109 mil | 283 mil |
| 10 A | 283 mil | 737 mil |
Before you commit the width
Neither a legacy equation nor an unadjusted reference fit guarantees a safe temperature on a finished PCB. Check the actual stackup, copper tolerances, local ambient and nearby heat sources, then validate critical paths by measurement or thermal analysis. The tool flags legacy results outside its stated coverage. The IPC-2152 fit is checked independently and withheld outside its supported domain. Use the fabricator’s actual minimum geometry and tolerances rather than a universal minimum trace width.
Where engineers use this
Motor drives and inverters
Sizing the DC-bus and phase-output traces that carry tens of amps, where a controlled temperature rise keeps the copper and nearby components within their ratings.
Switching power supplies
Width for input and output power traces and pours, where high RMS current and a warm enclosure push you past standard 1 oz copper.
LED lighting and strips
Long low-voltage runs where both trace heating and the resistance-driven voltage drop along the run decide the width.
Automotive and under-hood electronics
Power traces derated for a high ambient, where the temperature rise is added on top of an already-hot board, not room temperature.
Frequently asked questions
Can it work backwards from a trace width?
Shouldn't an external trace need more copper, since it can lift off the board when it overheats?
Should I use IPC-2221 or IPC-2152?
The calculator wants very wide thermal-relief spokes. Is that right?
What temperature rise should I design for, and what about a hot enclosure?
How accurate is the result?
How this relates to other standards
| Standard / tool | Relationship | What it means |
|---|---|---|
| IPC-2221B (2012) | Superseded by | IPC-2221C (2023) is the current edition; this constant-current method is unchanged between the two. |
| IPC-2152 | Refined by | A 2009 test-based current-capacity reference. IPC currently lists it as “No Longer Maintained”; this calculator exposes only one published approximation, not the full document workflow. |
| PCB Via Current | Same standard as | Sizes the plated via barrel by the same IPC-2221 method - size them together so the via is not the bottleneck. |
Related tools
Related standards
Sources: IPC-2221C, Generic Standard on Printed Board Design (current generic PCB design reference) · IPC-2152 (2009), current-carrying-capacity reference; IPC revision table now lists it as No Longer Maintained · L. Rozenblat, PCB trace width calculation based on IPC-2152 (universal still-air curve-fit of Fig 5-2). Verify against the current edition.