PCB Trace Width vs Current Capacity Calculator (IPC-2152 Standard)
Undersized PCB traces overheat, degrade, and can eventually fail open under sustained current, while oversized traces waste valuable board space. This calculator applies the IPC-2152 empirical formula to compute the minimum safe trace width for your current, temperature rise, copper weight, and layer location.
For 5.00A at 10°C rise on 1oz external copper, use at least a 108.9 mil (2.77mm) trace.
| Metric | Value |
|---|---|
| Continuous current | 5.00 A |
| Allowable temp rise | 10°C |
| Copper weight | 1 oz |
| Layer type | External |
| Cross-section area | 150 mils² |
| Minimum trace width | 108.9 mils (2.77 mm) |
| Voltage drop per inch | 23.895 V |
- 1.
Area(mils²) = (Current / (k × TempRise^0.44))^(1/0.725) - 2.
TraceWidth(mils) = Area / (CopperOz × 1.378) - 3.
Resistance/in(Ω) ≈ 717 / Area(mils²)
How to Use This Calculator
1. Enter your details
Use the labelled fields and units that match your situation.
2. Calculate instantly
The result, visual comparison, and working update as values change.
3. Review your result
Check assumptions, then copy, print, or share the calculation.
Formula & step-by-step maths
- k
- 0.048 external layer, 0.024 internal layer
- TempRise
- Allowable temperature rise in °C
Why external and internal traces differ
Internal traces are surrounded by insulating FR4 material and dissipate heat far less efficiently than external traces exposed to open air, so IPC-2152 uses a lower k-constant (0.024 vs 0.048) requiring roughly double the width for the same current and temperature rise.
Understanding the IPC-2152 curve
IPC-2152 replaced the older IPC-2221 standard with more accurate empirical curves derived from thermal testing on real boards, accounting for heat spreading, board thickness, and copper pour proximity more realistically than the older simplified formula.
Copper weight and trace width tradeoffs
Doubling copper weight (e.g. 1oz to 2oz) roughly halves the required trace width for the same current, since more copper volume conducts and dissipates heat more efficiently per unit of board area.
Voltage drop matters for long traces
Even a correctly-sized trace for thermal safety can cause unacceptable voltage drop over long distances, especially in low-voltage logic circuits — always check voltage drop separately for traces longer than a few inches.
IPC-2152 reference trace widths (external, 10°C rise, 1oz copper)
| Current | Approx. width (mils) | Approx. width (mm) |
|---|---|---|
| 1 A | 12 mils | 0.30 mm |
| 2 A | 24 mils | 0.61 mm |
| 3 A | 37 mils | 0.94 mm |
| 5 A | 68 mils | 1.73 mm |
| 10 A | 160 mils | 4.06 mm |
| 15 A | 260 mils | 6.60 mm |
Frequently Asked Questions
Three worked examples
Same engine, three different starting points — useful if you want to see how sensitive the answer is before you type your own numbers in.
Example 1: continuous current 3.9 A, allowable temperature rise "10°C"
On the lower / more conservative end. For 3.90A at 10°C rise on 1oz external copper, use at least a 77.3 mil (1.96mm) trace.
Example 2: continuous current 5 A, allowable temperature rise "10°C"
A typical middle-of-the-road setup. For 5.00A at 10°C rise on 1oz external copper, use at least a 108.9 mil (2.77mm) trace.
Example 3: continuous current 6.5 A, allowable temperature rise "20°C"
On the higher / more demanding end. For 6.50A at 20°C rise on 1oz external copper, use at least a 102.7 mil (2.61mm) trace.
Quick answers about the PCB Trace Width & Current Capacity
What exactly does the PCB Trace Width & Current Capacity work out?
Undersized PCB traces overheat, degrade, and can eventually fail open under sustained current, while oversized traces waste valuable board space. You enter continuous current, allowable temperature rise, copper weight and trace location and the result panel updates straight away, so you can compare two or three versions of the same question in a few seconds.
What do I need before I start?
Only 4 fields: continuous current, allowable temperature rise, copper weight and trace location. Nothing else is needed and nothing is stored.
How is it calculated — why external and internal traces differ?
Internal traces are surrounded by insulating FR4 material and dissipate heat far less efficiently than external traces exposed to open air, so IPC-2152 uses a lower k-constant (0. The same maths runs inside this page, so hand-checking the result on paper gives you the identical figure.
Why do two calculators give me different answers for pCB Trace Width & Current Capacity?
IPC-2152 replaced the older IPC-2221 standard with more accurate empirical curves derived from thermal testing on real boards, accounting for heat spreading, board thickness, and copper pour proximity more realistically than the older simplified formula. Different sites pick different assumptions, so always check which method a calculator states before you trust the gap between two numbers.
What does the "IPC-2152 reference trace widths (external, 10°C rise, 1oz copper)" table on this page tell me?
It is the reference range this tool works against — 6 rows from "1 A" (12 mils) up to "15 A" (260 mils). Use it to sanity-check whether the number you just calculated sits where you expected it to.
Which allowable temperature rise should I pick?
The dropdown offers 3 choices — 10°C, 20°C and 30°C. Pick the one that matches your real situation rather than the one you would like to be true; allowable temperature rise usually moves the final figure more than any other single input, so it is worth running it twice with the option above and below your guess.
Do I have to press a button or reload the page to see the result?
No. PCB Trace Width & Current Capacity runs completely inside your browser, so the moment you change a value the cards recalculate — there is no submit step, no page reload and no waiting for a server round trip. That also means it keeps working on a weak or intermittent mobile connection.
Is it free, and do you keep what I type?
It is free with no sign-up, no app install and no usage limit. Nothing you enter into PCB Trace Width & Current Capacity leaves your device — the calculation is JavaScript running locally, so there is no upload of your figures to DrHint or anyone else.
Can I use it on a phone?
Yes — the layout stacks to a single column on small screens and the number fields open the numeric keypad on both Android and iOS. Many people bookmark this page or add it to their home screen and re-open it whenever the question comes up.
Anything to be careful about with the result?
For 5A continuous current with 1oz external copper and a 10°C temperature rise, a trace width of roughly 68 mils (1. Treat the output as a well-grounded estimate for planning, not as a professional, legal or medical decision on its own.
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