# PCB Trace Current Calculator (IPC-2221) URL: https://speedycalculator.com/calculators/other/pcb-trace-current/ Last updated: 2026-10-30 > The PCB trace current calculator finds the maximum current a copper trace can carry for a given width, copper thickness and allowed temperature rise, for internal or external layers using the IPC-2221 formula, plus cross-section, trace temperature, resistance, voltage drop, power loss and current density. ## Inputs - Trace width (mil, mm, µm, in) - Copper thickness (oz/ft², mil, µm, mm) — 1 oz/ft² = 1.378 mil = 35 µm; 2 oz = 70 µm. - Maximum temperature rise (°C, °F, K) - Trace location - Ambient temperature (°C, °F, K) - Trace length (cm, mm, in, mil) ## Results - Cross-sectional area - Maximum current - Trace temperature - Resistance at that temperature - Voltage drop at maximum current - Power dissipation - Current density - IPC-2221 chart range ## Formula ``` I = k × ΔT^0.44 × A^0.725 (A in mil², ΔT in °C, k = 0.048 external, 0.024 internal) · A = W × T · R = ρL ÷ A × [1 + α(T_trace − 20 °C)] · V = I × R · P = I² × R ``` ## Explanation Current flowing through a PCB trace heats it. The heat escapes into the board and the air, and the trace settles at a temperature above ambient that rises with current. Exceed the laminate's limits and you risk delamination, damaged solder joints or a trace that acts as a fuse – so designers size power traces for an acceptable temperature rise, commonly 10–20 °C. The classic sizing rule comes from IPC-2221 (formerly IPC-D-275), which fitted curves to tests from the 1950s: I = k × ΔT^0.44 × A^0.725, with the cross-section A in square mils. External traces get k = 0.048 because they shed heat to the air; internal traces get k = 0.024, half the current for the same size. This calculator solves that equation for the current, and also reports the trace's resistance, voltage drop and power loss for a given length. Its successor, IPC-2152 (2009), measured many more configurations and found that internal traces are not nearly as bad as the old charts suggest, while board thickness, copper planes and nearby traces matter a lot. The IPC-2221 values are therefore conservative for internal layers and remain a safe, widely accepted first estimate; use IPC-2152 charts or thermal simulation for critical high-current designs. ### How to use the PCB Trace Current Calculator - **Trace width** - **Copper thickness** — 1 oz/ft² = 1.378 mil = 35 µm; 2 oz = 70 µm. - **Maximum temperature rise** - **Trace location** - **Ambient temperature** - **Trace length** Results update as you type, every field has its own unit menu, and everything is calculated in your browser. ### How it works Enter the trace width, copper thickness, allowed temperature rise and location, plus the ambient temperature and length. The calculator computes the cross-section, applies the IPC-2221 formula for current, then uses copper resistivity at the trace temperature for resistance, voltage drop and power. ### Worked example A 10 mil wide outer-layer trace in 1 oz copper (1.378 mil) has a cross-section of 13.78 mil². For a 10 °C rise: I = 0.048 × 10^0.44 × 13.78^0.725 = 0.048 × 2.754 × 6.70 = **0.886 A**. An inner-layer trace carries half: 0.443 A. At 35 °C a 5 cm length has a resistance of 0.102 Ω, so at 0.886 A it drops 91 mV and dissipates 80 mW. ### Current for 1 oz copper, 10 °C rise (IPC-2221) WidthExternalInternal10 mil (0.25 mm)0.89 A0.44 A20 mil (0.51 mm)1.46 A0.73 A50 mil (1.27 mm)2.83 A1.41 A100 mil (2.54 mm)4.70 A2.35 A ### Inputs explained FieldWhat to enterTrace widthUnits: mil, mm, µm, inCopper thicknessUnits: oz/ft², mil, µm, mm. 1 oz/ft² = 1.378 mil = 35 µm; 2 oz = 70 µm.Maximum temperature riseUnits: °C, °F, KTrace locationChoose one: External (outer layer), Internal (inner layer)Ambient temperatureUnits: °C, °F, KTrace lengthUnits: cm, mm, in, mil ### What each result means - **Cross-sectional area** = [Trace width]×[Copper thickness] - **Maximum current** = [k constant]×[Maximum temperature rise]^0.44×[Cross-sectional area]^0.725 - **Trace temperature** = [Ambient temperature] + [Maximum temperature rise] - **Resistance at that temperature** = 1.72e-6×[Trace length]÷([Cross-sectional area]×6.4516e-6)×(1 + 0.00393×([Trace temperature] - 20)) - **Voltage drop at maximum current** = [Maximum current]×[Resistance at that temperature] - **Power dissipation** = [Maximum current]^2×[Resistance at that temperature] - **Current density** = [Maximum current]÷([Cross-sectional area]×0.00064516) ## Worked example Inputs — Trace width: 10 mil; Copper thickness: 1 oz/ft²; Maximum temperature rise: 10 °C; Trace location: External (outer layer); Ambient temperature: 25 °C; Trace length: 5 cm. Results — Cross-sectional area = 13.78 mil²; **Maximum current = 0.8855 A**; Trace temperature = 35 °C; Resistance at that temperature = 102.4371 mΩ; Voltage drop at maximum current = 90.7098 mV; Power dissipation = 80.3251 mW; Current density = 99.6 A/mm²; IPC-2221 chart range = Within the IPC-2221 chart range. ## Key terms - **Temperature rise (ΔT)**: How much hotter the trace runs than its surroundings. - **Copper weight (oz/ft²)**: Copper thickness expressed as mass per area: 1 oz ≈ 35 µm. - **Cross-section**: Trace width × thickness, in mil² for the IPC formula. - **Current density**: Current per cross-sectional area, in A/mm². ## FAQ **How much current can a 10 mil trace carry?** About 0.89 A on an outer layer with 1 oz copper and a 10 °C rise, or 0.44 A on an inner layer (IPC-2221). **Why are internal traces rated lower?** IPC-2221 assumes they cannot shed heat to air; IPC-2152 tests show they actually do nearly as well, so the old rule is conservative. **What temperature rise should I allow?** 10 °C is a conservative default; 20–30 °C is common for power traces if the board and parts tolerate it. **Does doubling the width double the current?** No – current grows with area to the power 0.725, so twice the width gives about 1.65 times the current. **What about short traces?** Very short traces near large pads or planes run cooler than the formula predicts, because copper conducts heat away. **Should I use 2 oz copper?** Yes for high currents – it halves the width needed for the same cross-section. ## Sources - [IPC-2221B – Generic Standard on Printed Board Design (table of contents)](https://www.ipc.org/TOC/IPC-2221B.pdf) - [IPC-2152 – Standard for Determining Current-Carrying Capacity in Printed Board Design](https://www.ipc.org/TOC/IPC-2152.pdf)