PCB Trace Width Calculator
Find a starting trace width for your current, or estimate how much current an existing trace can carry. Compare external and internal layers, including resistive losses.
IPC-2221 empirical method & limitations ↓Compare external & internal traces
IPC-2221 empirical estimate · nominal finished cross-section
External trace
Width W · copper thickness t
Copper on the board surfaceInternal trace
Width W · copper thickness t
Enter your requirements and select Calculate. Both layer estimates will appear here.
Use these estimates for early routing decisions. Plane proximity, board construction, airflow and nearby heat sources are outside this model. Confirm final geometry and thermal performance for your application.
METHOD & SOURCES
How the trace width estimate works
The calculator uses the common IPC-2221 empirical relationship between current, copper cross-section and temperature rise. It is a planning estimate, with separate coefficients for external and internal traces.
I = k × ΔT0.44 × A0.725
I is current in amperes; ΔT is temperature rise in °C; A is the copper cross-sectional area in mil². The coefficient k is 0.048 for external traces and 0.024 for internal traces. Width is cross-sectional area divided by finished copper thickness.
Resistance is R = ρ(T) × L / A, using copper resistivity 1.724 × 10⁻⁸ Ω·m at 20 °C and a linear temperature coefficient of 0.00393/°C. Conductor temperature is ambient plus the selected rise. Voltage drop is I × R; power loss is I² × R. These losses are calculated at the displayed current for each layer.
Unit changes convert the existing physical value. Nominal copper weight uses 1 oz/ft² = 35 µm; this is a PCB convention, and actual finished copper should be confirmed with your fabricator.
This calculator accepts ambient −40 to 125 °C, temperature rise greater than zero up to 100 °C, and a combined conductor temperature no higher than 150 °C. These are calculator operating limits. They do not certify the model for every board or establish your laminate's temperature rating.
It does not implement IPC-2152 thermal charts or solve airflow, nearby planes, board thickness, trace spacing, transient current or heat-source coupling. Values shown are nominal estimates; choose design margin and verify the actual board.
- Texas Instruments TIDUCS7, page 9, Equation 7: IPC-2221 coefficients
- IPC-2152 contents: additional current-carrying and thermal considerations
- Copper Development Association, Earthing Practice, Table 12-5: copper electrical properties
For worked examples and current tables, read our PCB trace width design guide (English).
Published by HilPCB · Method notes updated November 8, 2026
COMMON QUESTIONS
PCB trace width questions
Understand the estimates before choosing your trace dimensions.
Why is the internal trace wider?
The empirical model uses a lower coefficient for internal conductors. For the same current, copper thickness and allowed rise, it therefore estimates a larger internal cross-section. Real board cooling also depends on copper planes and construction.
Does a longer trace need to be wider?
Trace length does not enter this model's current-to-width equation. It increases resistance, voltage drop and dissipated power, so your electrical requirements may still call for a wider trace.
Can I use this to calculate controlled impedance?
Current capacity and controlled impedance use different models. Use our impedance and stackup workbench to evaluate signal geometry and reference layers.
Is the displayed current a guaranteed safe limit?
No. It is an estimate at your chosen temperature rise under a simplified empirical model. Check final dimensions, material limits, temperature margin and operating conditions with your design and manufacturing engineers.