PCB Track Width Calculator
Table of Contents
PCB Track Width Calculator Online – Free IPC-2221 Trace Sizing Tool
This PCB track width calculator online gives you the correct copper track width for any current in seconds. Built on the IPC-2221 standard, it's a free PCB track width calculator online that returns results in both mil and mm — no signup, no install, just an instant answer.
What Is PCB Track Width and Why Does It Matter?
Every copper path on a printed circuit board is called a track, or a trace depending on which side of the world you learned PCB design in. Whatever you call it, its width is not a cosmetic choice — it's an engineering decision that determines how much current the copper can carry before it heats up beyond a safe limit.
A track that's too narrow for the current running through it acts like a tiny heating element. It gets hot, the surrounding solder mask can discolor or lift, and in extreme cases the copper itself can burn open, taking your circuit down with it. A track that's too wide wastes board space and, on a dense layout, forces you to make compromises elsewhere. This is exactly the problem a PCB track width calculator online is built to solve — it gives you the narrowest safe width for a given current, so you're not guessing and not over-engineering.
Whether you search for it as a track width tool or a trace width calculator, the underlying question is the same: for this much current, on this layer, with this copper weight, how wide does the copper need to be?
Understanding the IPC-2221 Standard Behind This Calculator
IPC-2221, formerly known as IPC-D-275, is the generic standard published by IPC — the Association Connecting Electronics Industries — for the design of printed circuit boards. It's the reference document this PCB track width calculator online is built around, just like most professional trace width tools used across the industry.
The standard is based on empirical test data: engineers ran real current through real copper traces of known dimensions and recorded how hot they got. From that data, curve-fitted formulas were derived that let you predict temperature rise for a given track width and current, or work backwards to find the width you need for a target temperature rise.
Two separate curves exist in IPC-2221 — one for traces on the outer (external) layers of a board, and one for traces buried inside the board (internal layers). This distinction matters a lot, and we'll cover exactly why a little further down.
The PCB Trace Width Current Calculator Formula Explained
At the core of this PCB trace width current calculator is the same empirical relationship between current, cross-sectional area, and temperature rise used across the industry:
To turn this into a working PCB track width calculator online, the formula is rearranged to solve for the cross-sectional area A once you know the current and the temperature rise you're willing to accept. That area is then divided by the copper thickness (based on copper weight in ounces per square foot) to get the final track width in mils, which the calculator then converts to millimeters automatically.
This is exactly the calculation running behind the scenes on this page — you supply the current, the tool applies the IPC-2221 formula for 1 oz copper and a 10°C rise, and returns the track width instantly in both mil and mm.
How to Use This PCB Track Width Calculator Online
Getting a result from this free tool takes less time than opening a spreadsheet. Here's the process:
- Enter your current (A) — This is the maximum current the track will need to carry continuously, not just a momentary peak.
- Click Calculate — The PCB track width calculator online applies the IPC-2221 external-layer formula for 1 oz copper and a 10°C temperature rise.
- Read the result — You'll get the recommended track width in both mil and mm, ready to punch straight into your PCB design software.
- Check the reference table — Use the "IPC-2221 Reference Table" link below the result to compare against standard current values at a glance.
Calculator Inputs Explained
This PCB track width calculator online keeps things simple with a single input — current — while assuming standard defaults for the rest. Here's what's happening under the hood with each parameter:
| Parameter | Default Used | Why It Matters |
|---|---|---|
| Current (A) | User input | The main driver of track width — higher current always needs more copper cross-section |
| Copper Weight | 1 oz/ft² | Thicker copper (2 oz) allows a narrower track for the same current |
| Temperature Rise (ΔT) | 10°C | A conservative, widely used design margin suitable for most consumer and industrial boards |
| Layer Location | External | Internal traces need to be wider for the same current since heat escapes more slowly |
Internal vs External Trace Width — What's the Difference?
This is one of the most common points of confusion for anyone new to sizing copper tracks, and it's worth clearing up properly.
| Property | External Trace | Internal Trace |
|---|---|---|
| Location | Top or bottom copper layer | Buried between internal layers |
| Heat Dissipation | Good — exposed to air, cools by convection | Poor — surrounded by insulating dielectric material |
| Required Width for Same Current | Narrower | Roughly 2x wider |
| IPC-2221 Constant (k) | 0.048 | 0.024 |
It feels counterintuitive at first — surely a buried trace, protected on both sides, should be safer? But heat doesn't care about protection, it cares about escape routes. An external track can shed heat straight into open air. An internal track is wrapped in fiberglass and epoxy, which is a decent electrical insulator but a poor thermal one, so the heat has nowhere to go. That's why internal traces always need to be wider for the same current if you're trying to hit the same temperature rise target.
PCB Copper Track Width Calculator — Copper Weight and Thickness
Copper weight is measured in ounces per square foot, and it directly sets the thickness of the copper layer: 1 oz copper is roughly 1.4 mils (35 microns) thick, and 2 oz copper is roughly double that. This matters because a PCB copper thickness calculator or track width tool needs this value to convert the required cross-sectional area into an actual physical width.
Since cross-sectional area is simply width multiplied by thickness, doubling the copper weight roughly halves the width you need to carry the same current at the same temperature rise. This is why high-current boards — power supplies, motor drivers, battery chargers — often specify 2 oz or even 3 oz copper on the outer layers, letting the designer keep track widths manageable without sacrificing current capacity.
Most low to medium current consumer electronics stick with the industry-default 1 oz copper, which is exactly what this PCB track width calculator online assumes unless you're working from a custom fabrication spec.
Real-World Example — Sizing a Track for 12A
Let's walk through a practical scenario. Say you're routing a 12V DC power path on a two-layer board that needs to carry 12A continuously — a fairly common requirement for a small motor controller or a DC-DC converter output.
Punch 12 into the PCB track width calculator online above and you'll get exactly this result. Notice how much wider this is than a typical signal trace — that's the whole point of a dedicated trace width current capacity calculator: it stops you from routing power the same way you'd route a logic signal, which is one of the most common mistakes on first-time board layouts.
If 9.25mm feels too wide for your layout, you have two practical options: increase the copper weight to 2 oz (which roughly halves the required width), or split the current across two parallel traces on different layers, each carrying half the load.
Trace Resistance, Voltage Drop and Power Loss
Track width doesn't just control temperature — it also controls how much voltage you lose along the length of the copper. A PCB trace resistance calculator layers on top of the basic width calculation by factoring in trace length and copper resistivity.
Resistance rises with trace length and falls as track width and thickness increase. Once you know the resistance, voltage drop is simply current multiplied by resistance, and power loss is current squared multiplied by resistance. On a long, narrow, high-current track, this power loss shows up as heat — which is exactly what the IPC-2221 temperature rise formula is trying to keep in check in the first place. The two calculations are really two sides of the same coin: width prevents overheating, and resistance tells you how much energy you're wasting getting there.
For power-sensitive designs — battery-powered devices especially — even a small voltage drop across a supply track can matter. Keeping traces short and appropriately wide isn't just about safety, it's about efficiency too.
Common Mistakes When Choosing PCB Track Width
- Using signal-trace widths for power paths. A 6 mil track might be fine for a logic signal but will overheat instantly carrying several amps.
- Ignoring the internal vs external difference. Copying an external track width onto an internal layer routing the same current is a common way to end up with a board that runs hot.
- Forgetting connector and via current limits. Even a perfectly sized track is only as good as the connector pins and vias it passes through — check their current ratings too.
- Designing for average current instead of peak sustained current. Motors, LEDs, and switching circuits often draw more than their nameplate average during startup or switching transitions.
- Skipping the temperature rise consideration for enclosed boards. A board inside a sealed enclosure with no airflow needs a lower target temperature rise than one with a fan or open-air mounting.
Pro Tips From PCB Design Engineers
1. Add a Safety Margin for Real-World Conditions
The IPC-2221 formula behind this PCB track width calculator online assumes still air at a defined ambient temperature. If your board sits inside a warm enclosure, near a heatsink, or in direct sunlight, add extra width beyond what any basic calculator suggests.
2. Use Copper Pours Instead of Traces Where Possible
For very high current paths, a solid copper pour (a filled polygon rather than a thin trace) spreads current across a much larger area and dissipates heat far more effectively than even a wide single track.
3. Double-Check Against Your Fabricator's Actual Copper Weight
Not every fab house defaults to 1 oz copper on every layer. Confirm the actual copper weight in your stackup before finalizing track widths for a production run.
4. Keep High-Current Traces Short and Direct
Shorter tracks mean less resistance, less voltage drop, and less heat — often a bigger win than simply making the trace wider.
Frequently Asked Questions
How do I calculate PCB trace width for current?
Enter your maximum continuous current into this PCB track width calculator online. It applies the IPC-2221 formula I = k × ΔT^0.44 × A^0.725 to solve for the cross-sectional area needed, then converts that into a track width in mil or mm based on your copper weight and whether the trace is internal or external.
What is the minimum trace width for 10A?
For an external layer with 1 oz copper and a 10°C temperature rise, roughly 320–340 mil (8–8.6mm) is typical. The exact figure depends on copper weight and how much temperature rise you're willing to allow — enter 10 into the calculator above for a precise number.
How much current can a PCB trace handle?
It depends entirely on track width, copper thickness, layer location, and how much temperature rise is acceptable. There's no single fixed number — a 10 mil external track on 1 oz copper handles roughly 1A safely, while a 100 mil track under the same conditions can handle several amps.
What is the difference between internal and external trace width?
Internal traces are buried inside the board and dissipate heat poorly compared to external traces, which are exposed to open air. As a result, an internal track typically needs to be roughly twice as wide as an external track to carry the same current at the same temperature rise.
How wide should a PCB track be for 5 amps?
On an external layer with standard 1 oz copper and a 10°C rise, a 5A track generally falls in the 100–150 mil range. Enter 5 into the PCB track width calculator online above to get the exact width for your specific conditions.
What is the IPC-2221 standard for PCB design?
IPC-2221 is the generic PCB design standard published by IPC that defines, among other things, empirical formulas for calculating trace width based on current, temperature rise, and copper thickness. It replaced the older IPC-D-275 standard and remains the industry reference for current-carrying capacity calculations.
How do I convert PCB trace width from mm to mil?
One mil equals 0.0254mm, so to convert mil to mm, multiply by 0.0254. To go from mm to mil, divide by 0.0254. This calculator does the conversion automatically and displays both units side by side in the results table.
Why do internal traces need more width than external traces?
Internal traces are surrounded by dielectric material that insulates electrically but conducts heat poorly. External traces are exposed to air, which cools far more efficiently through convection. Since both are sized to hit the same temperature rise target, internal traces need extra copper cross-section to compensate for the weaker heat dissipation.
What is temperature rise in PCB trace design?
Temperature rise is how much hotter a track gets above ambient temperature once current flows through it. It's a design input you choose based on your board's environment — 10°C is a commonly used, conservative default suitable for most general-purpose designs.
How does copper weight affect trace width?
Heavier copper weight means a thicker conductor layer. Since current-carrying capacity depends on cross-sectional area (width × thickness), increasing copper weight from 1 oz to 2 oz roughly halves the width needed to carry the same current safely.
What happens if a PCB trace is too thin?
A track that's too thin for its current load will exceed its safe temperature rise, potentially damaging the solder mask, delaminating the copper, or in severe cases burning open and breaking the circuit entirely. This is exactly the failure this PCB track width calculator online is designed to prevent.
How do I calculate voltage drop in a PCB trace?
Voltage drop equals current multiplied by trace resistance (V = I × R). Trace resistance depends on copper resistivity, trace length, and cross-sectional area — longer, narrower tracks have higher resistance and therefore a larger voltage drop for the same current.
Ready to Size Your Next Board's Power Traces?
Use this free PCB track width calculator online to get an instant, IPC-2221-based track width for any current — then cross-check with our via current and copper weight tools before you send your board to fab.
Explore All PCB Calculators →For the official IPC-2221 standard documentation, visit the IPC standards organization.
