PCB Trace Width Calculator
Review a Circuit Edge power path: compare minimum copper width, resistive loss and the allowance you will carry into layout.
Design inputs
01 / CONFIGURECalculation workspace
02 / EXPLOREThis legacy IPC-2221 power law is an early sizing model, not an IPC-2152 thermal simulation. Nearby copper, enclosure, airflow and neck-downs change actual heating. Results are estimates; confirm critical designs with your fabricator.
How it works · formula & assumptions
I = k × ΔT^0.44 × A^0.725; w = A / t. k = 0.048 external or 0.024 internal; A and t in mil units.
This legacy IPC-2221 power law is an early sizing model, not an IPC-2152 thermal simulation. Nearby copper, enclosure, airflow and neck-downs change actual heating.
Where will this power net become narrow?
Where will this power net become narrow?
A motor-driver output or actuator feed should be reviewed from the connector pad to the load, not only across the long straight track. Ask for sustained current, startup behavior, local ambient and the permitted supply drop before selecting copper width.
Release a copper rule with its operating assumptions
Keep the calculated minimum separate from the routed design width. The Circuit Edge handoff should identify every neck-down, the return conductor and the copper specification used for the estimate. If assembly changes the relief geometry, revisit the path rather than treating the original calculator number as permanent.
The question this Circuit Edge workspace addresses
Review a Circuit Edge power path: compare minimum copper width, resistive loss and the allowance you will carry into layout. This legacy IPC-2221 power law is an early sizing model, not an IPC-2152 thermal simulation. Nearby copper, enclosure, airflow and neck-downs change actual heating.
Formula and assumptions
I = k × ΔT^0.44 × A^0.725; w = A / t. k = 0.048 external or 0.024 internal; A and t in mil units.
Choose a real thermal budget
Temperature rise is an increase above the local ambient, not the absolute copper temperature. A board in a sealed enclosure may already be substantially warmer than the room. Enter the ambient near the conductor and decide how much extra heating the surrounding components can tolerate. The resistance calculation uses ambient plus the selected rise, referenced to copper resistivity at 20 °C. This is an assumed operating temperature, not a solved thermal equilibrium.
Read the voltage-drop result
The width model does not depend on conductor length, but electrical resistance does. Doubling length doubles resistance, voltage drop and dissipation at the same current. Compare the result with the power rail budget at the receiving device. Include the return path, connector resistance, fuses and any current-sense element separately. A trace that meets a temperature-rise estimate can still cause unacceptable regulator headroom loss or load-step droop.
Keep the narrowest section honest
A wide polygon does not remove the importance of a narrow pad exit. Inspect neck-downs, thermal spokes, transitions and copper clearances around mounting holes. Use the minimum finished copper thickness rather than assuming nominal copper weight is guaranteed everywhere. The displayed 15 percent margin is a practical starting allowance within the requested 10–20 percent range; it is not a substitute for a tolerance or thermal analysis.
Apply the result in layout
Record the calculated minimum and the chosen design width as separate values. Round upward to a sensible CAD rule, then inspect the entire path at that rule. For short pulses, model the waveform and transient heating instead of entering a peak value as if it were continuous current. For sustained high power, evaluate planes, busbars, copper inserts or alternative layer allocation. Measure the prototype at the expected enclosure temperature and airflow.
Work from your project brief
Start by confirming the units shown beside each input. Enter the operating condition you expect in the finished product, then change one variable at a time so the effect stays clear. The plus and minus controls make small adjustments, while the slider is useful for a quick sensitivity sweep. Blank fields, impossible ranges and unsupported geometries stop the calculation instead of silently preserving a previous result. A unit change converts the displayed value while the underlying calculation keeps a consistent canonical unit system.
Keep a Circuit Edge board-review record
Use Copy Results for a design-review note, CSV for a calculation register, and Share Link to preserve the input values in the URL. Download PDF creates a local report with the inputs, outputs, formula and limitations. The exported estimate is only useful when its assumptions remain attached. Keep the board revision, stackup revision, supplier tolerances and applicable load or interface requirement in the same review record. A later fabrication change can invalidate an earlier calculation even if the calculator inputs have not changed.
Separate the displayed digits from project confidence
Several digits are displayed to make comparisons and unit conversions useful. Those digits do not imply matching physical accuracy. Manufacturing variation, environmental conditions and the simplicity of the selected model can dominate the final result. Round the chosen design requirement in a direction that preserves engineering margin, then agree the tolerance with your fabricator. Use prototype measurements and the relevant analysis tools when a small change would affect reliability, regulatory compliance or product performance.
Worked example
At 1 A, 10 °C rise and 1 oz external copper, the required width is approximately 0.301 mm. A 15% margin raises this to approximately 0.346 mm. Use the defaults as a reproducible starting point, then substitute your own board data. When comparing a manual calculation, keep dimensional units consistent and avoid rounding intermediate values. If your result differs, check the input definitions before changing the model or applying an unexplained correction factor.
Continue with our calculation methodology, fabrication review checklist and high-speed layout guide. For board-specific support, contact Circuit Edge Technologies.
Frequently asked questions
What does the trace width tool calculate?
Review a Circuit Edge power path: compare minimum copper width, resistive loss and the allowance you will carry into layout. This legacy IPC-2221 power law is an early sizing model, not an IPC-2152 thermal simulation. Nearby copper, enclosure, airflow and neck-downs change actual heating.
Which formula does this calculator use?
I = k × ΔT^0.44 × A^0.725; w = A / t. k = 0.048 external or 0.024 internal; A and t in mil units. The Methodology page records the model and its limitations so that a design reviewer can reproduce the assumptions.
How should I check the input definitions?
Temperature rise is an increase above the local ambient, not the absolute copper temperature. A board in a sealed enclosure may already be substantially warmer than the room. Enter the ambient near the conductor and decide how much extra heating the surrounding components can tolerate. The resistance calculation uses ambient plus the selected rise, referenced to copper resistivity at 20 °C. This is an assumed operating temperature, not a solved thermal equilibrium.
What is a useful worked example?
At 1 A, 10 °C rise and 1 oz external copper, the required width is approximately 0.301 mm. A 15% margin raises this to approximately 0.346 mm. This example is a starting point for checking units, not a universal production recommendation.
Can I use the result as a fabrication or compliance approval?
This legacy IPC-2221 power law is an early sizing model, not an IPC-2152 thermal simulation. Nearby copper, enclosure, airflow and neck-downs change actual heating. Obtain the required engineering and manufacturing review before releasing a critical design.
How can I save and share my calculation?
Copy Results includes the inputs, outputs and limitations. CSV provides a local record, while Download PDF creates a local engineering report. Share Link encodes the canonical input values in the URL. Anyone with the link can reproduce that input set.
What should I verify before design release?
Record the calculated minimum and the chosen design width as separate values. Round upward to a sensible CAD rule, then inspect the entire path at that rule. For short pulses, model the waveform and transient heating instead of entering a peak value as if it were continuous current. For sustained high power, evaluate planes, busbars, copper inserts or alternative layer allocation. Measure the prototype at the expected enclosure temperature and airflow.
Inputs and related calculators
Design current, Temperature rise, Copper weight, Copper layer, Conductor length, Ambient temperature.