PCB Trace Width Calculator
The maximum continuous DC current the trace must carry. IPC-2221 valid range: 0–35 A.
Standard copper weights: 1 oz/ft² = 35 µm = 1.378 mils thick. Most PCBs use 1 oz outer layers.
Maximum allowed temperature increase above ambient. Typical values: 10°C (conservative), 20°C (standard), 30°C (permissive). Valid range: 10–100°C.
Unlocks resistance, voltage drop, and power loss outputs. Leave blank to skip.
Used to calculate voltage drop as a percentage of supply, and to look up track clearance from IPC-2221 Table 2-1.
Widens the recommended trace by this percentage to account for manufacturing tolerances and conservative design practice.
Split the total current across N identical parallel traces, reducing each individual trace width by factor N.
Enter Your Trace Parameters
Fill in the current, copper weight, and temperature rise to calculate the minimum PCB trace width per IPC-2221 and IPC-2152.
How to Use the PCB Trace Width Calculator
Choose Calculation Mode
Select 'Width from Current' (the standard mode) to find the minimum trace width for a given current. Or switch to 'Current from Width' (reverse mode) if you already have a trace width and want to know the maximum current it can safely carry.
Enter Your Electrical and Thermal Parameters
Input the maximum continuous current your trace must carry, the copper weight of your PCB (most boards use 1 oz/ft² = 35 µm), the allowable temperature rise above ambient (10°C is conservative, 20°C is typical), and the expected ambient temperature. These four values drive the IPC-2221 and IPC-2152 calculations.
Add Optional Inputs for Full Results
Enter the trace length to unlock resistance, voltage drop, and power loss outputs. Enter the supply voltage to see voltage drop as a percentage of your rail (keep below 3% for power rails). Optionally set a safety margin (20% is recommended for production boards) and select the number of parallel traces if splitting the current across multiple routes.
Read and Apply Your Results
The results panel shows the recommended trace width from three standards side by side: IPC-2221 External, IPC-2221 Internal, and IPC-2152 Universal. Use the 'Recommended Width' (with safety margin applied) for your PCB layout. Check the warnings section for any out-of-range conditions, minimum-width violations, or temperature concerns before finalizing your design.
Frequently Asked Questions
What is the difference between IPC-2221 and IPC-2152 trace width results?
IPC-2221 (derived from MIL-STD-275) was developed from tests on single, isolated traces with no nearby copper planes. Because it does not account for the cooling effect of adjacent copper, it tends to be conservative — often recommending traces 20–40% wider than actually necessary. IPC-2152 (published in 2009) introduced correction factors for copper weight, board thickness, the presence of a copper plane, and the distance to that plane, producing a more accurate result for real PCB designs. For a standalone trace far from any copper fill, the two standards give similar results. For a trace running above a large ground plane, IPC-2152 will recommend a noticeably narrower trace. When in doubt, use the more conservative IPC-2221 external result as your minimum, and treat IPC-2152 as the likely-achievable target.
Why do inner (internal) layer traces need to be wider than outer (external) traces?
External layer traces sit on the surface of the PCB where they can lose heat to the surrounding air through both convection and radiation. Internal layer traces are sandwiched between layers of FR-4 fiberglass, which has roughly 1000 times lower thermal conductivity than copper. With no convective path to ambient air, inner layers rely almost entirely on conduction through the laminate to dissipate heat. The IPC-2221 formula captures this difference through the k constant: k = 0.048 for external and k = 0.024 for internal. Since k appears in the denominator, halving it doubles the required cross-sectional area — meaning internal traces typically need to be about twice as wide as external traces for the same current and temperature rise. This is a critical consideration for multilayer boards with internal power planes.
What temperature rise should I use in my PCB trace width calculation?
The IPC-2221 standard recommends using a temperature rise of 10°C for precision or signal-sensitive applications and up to 20°C for general-purpose power traces. A value of 10°C is considered conservative and provides a larger safety margin; 20°C is the most commonly used value in commercial electronics; and 30°C is sometimes acceptable in industrial or automotive designs where board temperatures are well understood. The key constraint is your maximum trace temperature: if ambient could reach 70°C and you allow 30°C rise, your trace temperature reaches 100°C — still below the FR-4 Tg of approximately 130°C but leaving little headroom. For high-reliability designs, always compute the maximum trace temperature (ambient + ΔT) and ensure it stays at least 20°C below your board's rated Tg.
When does voltage drop across a PCB trace become a design problem?
As a rule of thumb, keep trace voltage drop below 3% of the rail voltage for power distribution networks. On a 3.3 V supply, that is no more than ~100 mV of drop; on a 12 V supply, you can tolerate up to ~360 mV. Exceeding these limits means downstream circuits receive a lower voltage than expected, which can push them outside their specified operating range and cause incorrect behavior or reduced efficiency. Voltage drop becomes especially critical for: low-voltage microcontrollers and FPGAs (3.3 V or 1.8 V rails with tight supply tolerance), high-current motor drivers or LED drivers, and USB power delivery traces. The calculator shows voltage drop in absolute millivolts and as a percentage of supply voltage (if you enter the supply voltage), and warns you when the drop exceeds 3%.
What is the minimum trace width most PCB manufacturers can produce?
Standard PCB manufacturing processes at mainstream fab houses (JLCPCB, PCBWay, OSH Park, etc.) can reliably produce traces down to 6 mils (0.15 mm). This is known as the '6/6 rule' — 6 mil minimum trace width and 6 mil minimum spacing. Some advanced fabricators offer 4 mil or even 3 mil minimum trace width for HDI (high-density interconnect) boards, typically at higher cost. If the IPC-2221 formula calculates a required width below 6 mils, the calculator displays a warning reminding you that you may have a manufacturing feasibility issue. In practice, this scenario usually occurs only for very low-current signals where trace impedance — not current capacity — should be the design driver instead.
How does running parallel traces help with high-current routing?
When a single wide trace is impractical because it would block routing channels or violate clearance rules for adjacent copper features, you can split the total current across multiple identical parallel traces. If the IPC-2221 calculation requires a 50 mil trace for 10 A, you could instead use two 25 mil traces (each carrying 5 A) or five 10 mil traces (each carrying 2 A). For this to work correctly the parallel traces must be roughly equal in length — if they are not, the shorter trace will carry proportionally more current due to its lower resistance, potentially overloading it. The calculator's Parallel Traces feature shows you the required width per trace for 1, 2, 3, or 4 parallel paths, making it easy to evaluate routing trade-offs.