- Choose a tab — Trace Calculator for IPC-2221 computations, Copper Reference for thickness data, or Design Guide for minimum spacing and clearance rules.
- Trace Calculator: Enter the current in amps your trace must carry, the allowable temperature rise above ambient, the copper weight (0.5 to 6 oz), and trace length. Select whether the trace is on an external (outer) or internal (inner) layer — internal traces have less cooling and require wider dimensions.
- Click Calculate — the tool shows minimum trace width (mm and mil), cross-section area, trace resistance, voltage drop, power dissipation, and a visual cross-section diagram. A warning reminds you to apply a safety margin above the IPC minimum.
- Copper Reference tab shows thickness in µm and mil for each standard copper weight (0.5 to 6 oz/ft²) with typical application notes.
- Design Guide tab lists IPC-2221 Class 2 rules for minimum trace width, spacing, via clearance, high-voltage clearance, and thermal relief.
PCB Trace Width Calculator — IPC-2221 Design Standard
Designing printed circuit board traces that can safely carry the required current is one of the most critical aspects of PCB design. An undersized trace can overheat, cause board damage, create intermittent failures, or even start a fire. Our PCB Trace Width Calculator uses the industry-standard IPC-2221 equations to determine the minimum trace width for your current, copper weight, temperature rise, and layer type — all computed instantly in your browser with complete privacy.
Understanding IPC-2221 Trace Width Calculations
The IPC-2221 standard provides empirically-derived formulas for calculating the minimum cross-sectional area of a copper trace needed to carry a given current with a specified temperature rise:
A = (I / (k × ΔT^b))^(1/c)
Where A is the cross-sectional area in mil², I is the current in amps, ΔT is the temperature rise above ambient in °C, and k, b, c are empirical constants that differ based on the layer:
- External (outer) layers: k = 0.048, b = 0.44, c = 0.725
- Internal (inner) layers: k = 0.024, b = 0.44, c = 0.725
The trace width is then calculated by dividing the cross-sectional area by the copper thickness: Width = A / Thickness.
Key Features
- IPC-2221 Compliance: Uses the standard empirical formula with correct constants for both external and internal PCB layers.
- Six Copper Weights: Supports 0.5 oz through 6 oz copper (17.5 µm to 210 µm), covering everything from thin signal traces to heavy copper power boards.
- Complete Electrical Analysis: Beyond trace width, calculates trace resistance (temperature-compensated using copper's 0.00393/°C coefficient), voltage drop across the trace length, and power dissipation as heat.
- Visual Cross-Section: SVG diagram shows the trace cross-section proportional to the calculated width and copper thickness, with the FR-4 substrate shown in green.
- Copper Reference Table: Quick-reference table showing the relationship between copper weight (oz/ft²), thickness (µm and mil), and typical application.
- Design Guidelines: IPC Class 2 minimum rules for trace width, spacing, via clearance, high-voltage clearance, and thermal relief spoke width.
Copper Weight and Thickness
Copper weight is specified in ounces per square foot (oz/ft²). The relationship to thickness is linear:
- 0.5 oz: 17.5 µm (0.7 mil) — fine-pitch SMD components and high-density signal routing
- 1 oz: 35 µm (1.4 mil) — standard PCB manufacturing, most consumer electronics
- 2 oz: 70 µm (2.8 mil) — power supply circuits, LED drivers, motor controllers
- 3 oz: 105 µm (4.2 mil) — high-current power electronics, automotive ECUs
- 4 oz: 140 µm (5.6 mil) — very high-current applications, bus bar alternatives
- 6 oz: 210 µm (8.4 mil) — extreme heavy copper, specialized power converters
Trace Resistance and Power Loss
The calculator computes trace resistance using the fundamental formula R = ρL/A, where ρ is the resistivity of copper adjusted for the actual operating temperature. Copper's resistivity increases linearly with temperature at approximately 0.393% per degree Celsius above 20°C. This temperature-compensated resistance is then used to calculate voltage drop (V = IR) and power dissipation (P = I²R) across the trace.
Why Trace Resistance Matters
Even small trace resistances become significant in high-current designs. A 1A current through 100 mΩ resistance produces only 0.1V drop and 0.1W loss. However, a 10A current through the same resistance produces 1V drop and 10W of concentrated heat — potentially damaging the board.
Internal vs. External Layers
Internal layers require wider traces for the same current because they are sandwiched between insulating layers of FR-4 substrate with limited thermal dissipation paths. External layers benefit from convective air cooling on one side. The IPC-2221 formula accounts for this by using a k-value of 0.024 for internal layers versus 0.048 for external layers — effectively requiring approximately double the cross-sectional area for internal traces.
Design Best Practices
- Always apply safety margin: Use 1.5x to 2x the calculated minimum width to account for manufacturing tolerances, etching undercut, and real-world cooling limitations.
- Consider thermal vias: For high-current internal traces, add thermal vias to conduct heat to external layers and improve dissipation.
- Use copper pours: Large copper areas (ground planes, power planes) provide better current distribution and thermal management than narrow traces.
- Verify with thermal simulation: IPC-2221 provides a starting point, but complex designs benefit from finite-element thermal analysis.
Privacy and Security
All calculations run entirely in your browser using JavaScript. No PCB design data is transmitted to any server. No accounts, no tracking, no data collection.