liminfoPCB Trace Width Calculator
Free web tool: PCB Trace Width Calculator
Cross-Section Area
16.30 mils²
Trace Width (mils)
11.83
Trace Width (mm)
0.300
About PCB Trace Width Calculator
The PCB Trace Width Calculator implements the IPC-2221 standard formula to determine the minimum conductor width required to carry a specified current without exceeding a defined temperature rise. The tool accepts four inputs: current in amperes, allowable temperature rise in degrees Celsius, copper weight in ounces per square foot, and whether the trace is on an external (outer) or internal (buried) layer. Results are displayed as cross-sectional area in square mils, trace width in mils, and trace width in millimetres.
PCB designers, electronics engineers, and hardware developers use this calculator during schematic-to-layout translation to verify that power traces — such as motor drive lines, power rails, and high-current bus bars — can safely handle the expected current. The IPC-2221 standard distinguishes between external and internal layers because internal traces have less convective airflow, requiring approximately twice the cross-sectional area for the same current and temperature rise. The tool applies coefficients k = 0.048 for external layers and k = 0.024 for internal layers.
The calculation follows the IPC-2221 formula: Area (mils²) = [I / (k × ΔT^0.44)]^(1/0.725), where I is current in amperes and ΔT is temperature rise in °C. Trace width is then derived by dividing the required area by the conductor thickness in mils (copper weight in oz × 1.378 mils/oz). All computation runs entirely in your browser — no data is sent to any server, making it safe to use with proprietary circuit specifications.
Key Features
- Implements the IPC-2221 industry-standard formula for current carrying capacity
- Separate coefficients for external (k=0.048) and internal (k=0.024) PCB layers
- Outputs cross-section area in mils², trace width in mils, and trace width in mm
- Supports copper weights of 0.5 oz, 1 oz, and 2 oz per square foot
- Real-time calculation — results update immediately as you change any input
- Helps prevent thermal damage by ensuring traces are sized for their load current
- 100% client-side processing — no data uploaded to any server
- Clean, focused interface with labelled inputs for current, temperature rise, copper weight, and layer
Frequently Asked Questions
What standard does this PCB trace width calculator use?
The calculator uses the IPC-2221 standard (Generic Standard on Printed Board Design), which is the industry-accepted reference for PCB conductor sizing. The formula is: Area (mils²) = [I / (k × ΔT^0.44)]^(1/0.725), where k = 0.048 for external layers and k = 0.024 for internal layers.
What is the difference between external and internal layers?
External (outer) layers are exposed to air and can dissipate heat through convection. Internal (buried) layers are sandwiched between dielectric material and rely mainly on conduction for heat transfer, making them less efficient. IPC-2221 accounts for this with different k coefficients: external layers use k = 0.048 and internal layers use k = 0.024, which roughly doubles the required trace width for internal conductors.
What is copper weight in oz and how does it affect trace width?
Copper weight in oz/ft² describes the thickness of the copper foil. 1 oz copper is approximately 35 µm (1.378 mils) thick. Thicker copper (2 oz = 2.756 mils) provides a larger cross-sectional area per unit width, so the required trace width is narrower for the same current. The calculator converts oz to mils using the factor 1.378 mils per oz.
What temperature rise should I use?
A temperature rise of 10°C is a common conservative target for general-purpose PCBs, while 20–30°C may be acceptable for designs where thermal headroom is available. The allowable rise depends on the maximum ambient temperature plus the rise staying below the glass transition temperature of the PCB substrate (typically 130–180°C for FR4).
How do I convert mils to mm?
1 mil = 0.0254 mm. The calculator provides the result directly in both mils and millimetres. For example, a trace width of 20 mils = 0.508 mm. Most PCB EDA tools accept both units; check your design rules for the required format.
Does this calculator account for impedance-controlled traces?
No. This tool is specifically for current-carrying capacity sizing based on IPC-2221. Impedance-controlled traces (e.g., 50 Ω microstrip or differential pairs) require a separate impedance calculator that considers trace width, dielectric thickness, and Dk. Always check both current capacity and impedance requirements for high-speed or RF traces.
What current should I use — RMS or peak?
Use RMS (root mean square) current for AC or switching waveforms. For DC power rails, use the maximum continuous DC current. Temperature rise is a thermal effect driven by I²R dissipation, which is proportional to the RMS value of the current waveform.
Should I add a safety margin to the calculated trace width?
Yes. IPC-2221 results are minimum values. It is common practice to add a 20–50% safety margin, especially for traces that carry current continuously, for boards operating in high-ambient-temperature environments, or where manufacturing tolerances may reduce actual copper thickness. Round up to the nearest standard design-rule increment.