PCB Trace Width Calculator
Free online PCB trace width calculator. Size copper traces from current and temperature rise using IPC-2221 formulas for external and internal layers.
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What is PCB Trace Width Calculator?
The PCB Trace Width Calculator is a free electronics engineering tool that sizes copper traces using the IPC-2221 generalized chart formulas. Enter the current, the allowed temperature rise, the copper weight, and whether the trace runs on an external or internal layer — and instantly get the minimum trace width in mils and millimeters, the cross-section area, and, for a given trace length, the temperature-corrected resistance, voltage drop, and power dissipation. Everything runs in your browser.
Key Benefits
- Size power traces correctly before sending the board to fab — no more guessing from old projects
- Internal and external layer constants applied automatically, so buried traces get the wider width they need
- Copper weights from 0.5 oz to 4 oz with exact µm conversions, matching common fab capabilities
- Trace resistance and voltage drop help catch IR-drop problems on long, high-current runs
- No signup, no server, no design file upload — the calculator runs fully offline
Common Use Cases
- •Sizing power rails and motor-driver traces in hobby and professional PCB designs
- •Checking whether an existing trace can carry more current after a design change
- •Teaching electronics classes how current capacity, copper thickness, and heat relate
- •Quick sanity checks on open-hardware designs before ordering prototypes
How to Use the PCB Trace Width Calculator
- Enter the current: Type the DC or RMS current the trace will carry, in amps. For pulsed loads, use the RMS value.
- Set the allowed temperature rise: Choose how many °C the trace is allowed to heat above ambient — 10 °C is a conservative default.
- Pick copper weight and layer: Select the copper thickness (0.5–4 oz) and whether the trace runs on an external or internal layer.
- Read the width and optional losses: See the minimum width in mils and mm instantly. Enter a trace length to also get resistance, voltage drop, and power dissipation.
Key Features
- IPC-2221 generalized chart formulas for external (k=0.048) and internal (k=0.024) layers
- Width results in both mils and millimeters with cross-section area in mil² and mm²
- Copper weights from 0.5 oz to 4 oz with exact µm thickness conversions (1 oz ≈ 35 µm)
- Optional trace length computes temperature-corrected resistance, voltage drop, and power dissipation
- One-click copy of a full engineering summary for design reviews
- Works fully offline in the browser — design values never leave the device
Frequently Asked Questions
What is the IPC-2221 trace width formula?
IPC-2221 uses the generalized chart relationship A[mil²] = (I / (k · ΔT^0.44))^(1/0.725), where A is the cross-section area, I the current, ΔT the temperature rise, and k a layer constant (0.048 external, 0.024 internal). The width is the area divided by the copper thickness.
Why do internal layers need wider traces?
Internal layers are sandwiched in the laminate and cannot shed heat into the air, so the IPC chart uses half the constant (0.024 vs 0.048). For the same current and temperature rise, an internal trace needs roughly twice the cross-section.
How does copper weight (oz) affect trace width?
Copper weight is the foil thickness: 1 oz ≈ 1.378 mil ≈ 35 µm. Because width = area ÷ thickness, doubling the copper weight (e.g., 1 oz → 2 oz) roughly halves the required width for the same current.
Should I derate the calculated trace width?
Yes. The IPC-2221 chart is a generalized starting point. Add margin for vias in the path, closely spaced parallel traces, copper plating variation, high-altitude or enclosed products, and any current spikes. Many designers target a 30–50% wider trace than calculated.