PCB Trace Width Calculator
Find a trace width for your current, or estimate current for an existing width. Use finished copper thickness and a selected temperature rise.
How to Use the Trace Width Calculator
- Choose the task. Select Find width to size a trace for a known current, or Estimate current to see the current associated with an entered width.
- Enter the trace conditions. Provide finished copper thickness and the allowed temperature rise, along with the known current or width requested by your task. Check the displayed model and units. Results update as you edit.
- Add optional details. Enter trace length when you want resistance, voltage drop, or power loss estimates. Review the inputs and result, then export the calculation if you need to keep or share it.
Calculate Trace Width or Current Capacity
Live results · edit any inputCurrent, Copper and Temperature Rise
Required inputs. Start with the filled example, then enter your trace conditions.
1 oz/ft² ≈ 35 µm. These shortcuts do not add plating or specify a finished construction.
Width and Current Results
Continuous DC estimate at the selected rise. Planes, cooling, nearby heat sources and local bottlenecks are not resolved.
Outside this tool’s numerical reference-check window. Extrapolation deserves additional review; see model scope.
Optional Electrical Checks
Add length for resistance, voltage drop & loss
25 °C is an editable example. Copper temperature for resistance = ambient + selected rise; this is not a separate thermal simulation.
Add trace length to calculate resistance, voltage drop and loss.
- DC resistance
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- Voltage drop
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- Trace power loss
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Export locally, then attach the file yourself if you contact FLJ.
Results update automatically. Your calculation entries stay in this browser page.
Calculation Models and Assumptions
IPC-2152-Based External Trace Fit
The modern option uses the published Brooks–Adam external-trace fit (Equation 3-2, Table 3-1):
ΔT = 215.3 × I² / (Wmil1.15 × tmil)
Here I is current in amperes, and W and copper thickness t are in mils. For target rise, width is: W = [215.3 × I² / (ΔT × t)]1/1.15. This published fit is not the complete IPC-2152 method; it does not model planes, vias, pulses, AC skin effect, or current crowding. The 1 oz external case is a fit application, not a separate original IPC-2152 test dataset. See the published formula reference and the IPC-2152 scope.
IPC-2221 Legacy Estimates
The legacy estimate is I = k × ΔT0.44 × (Wmil × tmil)0.725, jossa k = 0.048 for an outer trace and k = 0.024 for an inner trace. Current is in amperes; width and thickness are in mils, and rise is in °C. Its width form is: W = [I / (k × ΔT0.44)]1/0.725 / t. The inner-layer constant belongs to this legacy estimate only; the modern option does not provide an inner-layer thermal fit.
DC Resistance, Voltage Drop and Power Loss
Electrical results use a separate rectangular-trace resistance estimate: R = ρ₂₀[1 + α(Tcu − 20°C)]L/(w × t), where Tcu = ambient + selected rise. Approximate copper constants are ρ₂₀ = 1.673 × 10−8 Ω·m at 20°C and α = 0.0039/K. Use consistent SI units for length, width, and thickness. Length is required only for these electrical results. Voltage drop is I × R, and trace loss is I² × R. Width mode uses the entered current; current mode uses the estimated current at the selected rise. Ambient affects resistance, not the thermal width fit.
Copper-property references: 20 °C resistivity table ja approximate copper-foil temperature coefficient. These are nominal approximations, not measured values for your foil.
Numerical reference-check window: 5–400 mil width, 17.5–105 µm finished copper and 10–100 °C rise. This is the tool’s software cross-check window, not a published accuracy envelope or a manufacturing limit. Values outside it receive an extrapolation notice. DC resistance uses an application guard of −50 to 150 °C ambient and ≤200 °C ambient + rise; these limits do not qualify the board for that temperature.
From Calculated Width to Finished Copper
FLJ translates the proposed trace geometry into fabrication requirements for finished copper, etched width and spacing. Imaging and etch compensation control the conductor pattern; plating changes the finished outer copper. Our heavy copper PCB fabrication service provides another construction option when wider traces compete with board space.
Review neck-downs at pads, thermal spokes and interlayer connections along the complete current path. A trace-width result does not size a via barrel. Our PCB design services connect these transitions with routing and placement; the stackup tool keeps finished copper and dielectric thicknesses together.
Send the exported calculation with your board files, material requirements and operating conditions for a board-specific fabrication discussion.
Discuss your PCB →PCB Trace Width Calculator FAQs
Should I enter continuous current or peak current?
Enter the continuous DC current for the trace segment. These models estimate current at a selected rise; they do not cover pulse heating or peak capacity. Analyze transient loads separately.
What is the difference between ambient temperature and temperature rise?
Ambient is the surrounding temperature; rise is the allowed copper increase above it. The thermal model uses rise. Ambient plus rise sets copper temperature for optional resistance, voltage-drop, and loss estimates.
Is nominal copper weight the same as finished copper thickness?
No. Copper weight is a nominal designation; plating and etching affect finished trace thickness. Enter finished thickness when known. An ounce preset is approximate.
Why do the two models give different results?
Brooks–Adam is a published external-trace fit. IPC-2221 is a legacy estimate with separate outer- and inner-layer constants. Their equations differ, and neither captures every board or cooling condition.
Does the calculated current mean the trace is safe in my product?
No. It estimates a uniform rectangular trace at the selected rise; it is not a fuse limit or product safety rating. Validate the full current path, including narrow sections, pads, connections, and cooling.
Can this tool size vias, thermal spokes or arbitrary copper pours?
No. It covers straight rectangular traces. Vias, spokes, pours, planes, and current crowding need separate analysis.
Are my calculation inputs uploaded?
Calculations run in your browser; the tool does not upload entered values. Loading the page still makes normal site and asset requests, which may be logged.