---

PCB Trace Width Calculator: IPC-2221 Minimum Width, Resistance and Via Capacity

A PCB trace that’s too narrow for its current can overheat, degrade or burn out. This tool uses the industry-standard IPC-2221 formula to find the minimum safe trace width for your current and allowed temperature rise, on both external and internal layers. It also works in reverse – enter a width to find the maximum safe current and includes trace resistance, voltage drop, power loss and a separate via current-capacity check, all in one place instead of across multiple tools.

---

How to Use

1. Choose your mode: enter current to find the required width or enter width to find the maximum safe current (reverse mode).
2. Enter the allowed temperature rise (°C) – how much hotter the trace is allowed to get above ambient.
3. Select copper weight (commonly 1oz or 2oz) and whether the trace is External or Internal.
4. (Optional) Enter the trace length (mm) to also see resistance, voltage drop and power loss.
5. Click Calculate to see the recommended width (mils and mm) or maximum current, with a scale preview.
6. For vias, scroll to Via Current Capacity enter via diameter and plating thickness and calculate separately.

---

Key Features

• IPC-2221 standard formula for minimum trace width, with correct constants for External vs Internal layers
• Reverse mode – enter a trace width and get the maximum safe current
• Results shown in both mils and millimetres
• Optional trace resistance, voltage drop and power loss when you enter trace length
• Separate via current-capacity estimator based on via diameter and copper plating thickness
• Visual scale preview showing the calculated trace width relative to a PCB reference
• Supports common copper weights (1oz, 2oz, etc.)
• Export as PDF or copy the result

---

Formula / Logic Used

Minimum Trace Width (IPC-2221, Current → Width)$$Area\ (mils^2) = \left(\frac{I}{k \times \Delta T^{0.44}}\right)^{1/0.725}$$

$$Width\ (mils) = \frac{Area}{Thickness\ (mils)}$$

Where $I$ is current in Amperes, $\Delta T$ is allowed temperature rise, $k$ = 0.048 for external layers or 0.024 for internal layers (internal traces are surrounded by insulation and dissipate heat less efficiently, so they need more copper for the same current) and $Thickness$ is copper weight converted to mils (1 oz ≈ 1.378 mils).

Reverse Mode (Width → Maximum Current)$$I = k \times \Delta T^{0.44} \times Area^{0.725}$$

Trace Resistance, Voltage Drop and Power Loss$$R = \frac{\rho \times L}{A}, \qquad V_{drop} = I \times R, \qquad P = I^2 \times R$$

Where $\rho$ is copper resistivity (≈1.72×10⁻⁸ Ω·m), $L$ is trace length and $A$ is cross-sectional area.

Via Current Capacity$$Area = \pi \times Diameter \times Plating\ Thickness$$

The via’s copper barrel is treated like an unrolled trace and this area is used in the same IPC-2221 formula (external-layer constant) to estimate current capacity .

---

Who Should Use This Tool

Diploma and B.Tech ECE/Electrical students learning PCB design and current-carrying capacity. Also useful for hobbyists and design engineers who need to size power traces and vias together without switching between multiple calculators.

---

Frequently Asked Questions (FAQs)

---

Related Tools

• RLC Color Code Calculator – verify component values before placing them on your PCB layout
• Op-Amp Gain/Filter Designer – design the circuit this PCB trace will carry
• Antenna Length Calculator – useful if your board includes an RF section

Read More>>>