Pcb Trace Width Calculator - Width, Cross-Section, Resistance

A PCB trace width calculator is a board-design tool that uses a closed-form curve fit of the older IPC trace-current charts to back-solve for the trace width your layout needs. Enter the maximum current, the copper weight, the temperature rise, and the trace location, and it returns the required width in mm and mils plus the cross-section, the resistance, the voltage drop, and the I²R power dissipation.

• • Sizing a power-distribution trace: Pick the current, set a 10 °C budget, and read the width the layout needs on 1 oz/ft² copper.
• • Comparing 1 oz vs 2 oz copper: Switch the copper weight and watch the width halve.
• • Estimating the heat budget: Read the I²R power dissipation and feed it into a thermal model.
• • Checking an LED-driver or USB VBUS segment: Run a 1 A or 0.5 A segment through the calculator to confirm the existing trace is wide enough.

The PCB trace width calculator uses the closed-form curve fit I = k × ΔT^0.44 × A^0.725 with k = 0.024 for internal traces and k = 0.048 for external traces. That algebraic form is the Brooks-style empirical fit of the older IPC-D-275 and IPC-2221 trace-current charts. IPC-2152 reports the same heating relationship from new test data but as correction-factor charts, not one equation, so designers use this curve fit for a first-pass width and confirm tight designs against IPC-2152 charts or thermal simulation. Once A is known, the width is A divided by the copper thickness (1 oz/ft² maps to 35 µm), and the same sized trace feeds an Ohm's law step that returns resistance, voltage drop, and I²R power dissipation.

Once the width is set, the PCB trace resistance calculator feeds the same copper weight and length back into a resistance, voltage drop, and per-metre ohm readout so the design review sees both numbers on the same layout.

The calculator uses the Brooks-style closed-form fit of the older IPC-D-275 and IPC-2221 trace-current charts to find the cross-section, divides by copper thickness for the width, and adds a temperature-corrected Ohm's law step so resistance, voltage drop, and I²R power all come from the same sized trace.

• I, dT, t: Maximum current (A), temperature rise above ambient (°C), and copper weight (oz/ft²).
• k: Layer constant from the closed-form fit: 0.024 internal, 0.048 external.
• A, W: Cross-section in mils² and the resulting width in mils. Width in mm is the mils value multiplied by 0.0254.
• R, V, P: Resistance (Ω), voltage drop V = I × R (V), and I²R power (W) at the operating temperature.

The 0.44 and 0.725 exponents are the empirical constants Brooks used to fit the IPC-D-275 / IPC-2221 trace-current charts to one equation; the 0.024 and 0.048 constants separate buried internal layers (trapped heat) from external layers (open to air).

According to the UltraCAD PCB Trace Calculator page, the closed-form I = k × ΔT^0.44 × A^0.725 with k = 0.024 internal and 0.048 external is the Brooks & Adam curve fit designers use to back-solve IPC trace-current charts; UltraCAD fits the IPC-2152 data closely once correction factors are applied.

According to Engineering Toolbox resistivity reference, copper has a bulk resistivity of 1.724 × 10⁻⁸ Ω·m at 20 °C with a temperature coefficient of 3.93 × 10⁻³ 1/°C - the pair the temperature-correction step uses to scale the resistance away from the 25 °C reference.

For non-rectangular conductors or arbitrary cross-sections, the electrical resistance calculator solves the same uniform-conductor R = ρL/A form once the equivalent area is known.

Four short ideas cover every number the calculator returns.

These four ideas cover every value the calculator prints. For most boards the defaults - 1 oz/ft² copper, 25 °C ambient, 10 °C rise - are the right place to start.

When the sized trace sits in series with a load, the voltage divider calculator models the pair as a series resistor chain so the actual load voltage reads off the divider output.

Five short steps take a current value and a temperature-rise budget to a sized trace.

1. 1 Enter the maximum current: Use steady-state DC for power rails or RMS for pulsed loads; 2 A is a typical LED-driver level.
2. 2 Pick the copper weight: 1 oz/ft² is the default for most consumer boards. 2 oz/ft² halves the width you need.
3. 3 Set the temperature-rise budget: 10 °C is a common conservative budget; lower values force a wider trace because ΔT sits in the denominator.
4. 4 Choose internal or external layer: The k constant in the curve fit switches from 0.048 to 0.024 when you go internal because the buried layer traps heat.
5. 5 Add trace length and ambient, read the result panel: Length and ambient drive the resistance, voltage drop, and I²R power.

For a 2 A external power rail on 1 oz/ft² copper with a 10 °C budget, leave current = 2, thickness = 1, tempRise = 10, traceLocation = external, traceLength = 50, ambientTemp = 25. The calculator returns about 0.78 mm of width, 0.032 Ω of resistance, 0.065 V of drop, and 0.13 W of heat. Step copper to 2 oz/ft² and the width drops to roughly 0.39 mm.

When the load is specified in watts at a known supply voltage, the watts to amps converter turns that into the current the trace has to carry before it goes into the Current input here.

A purpose-built trace width tool keeps the closed-form curve fit, the copper weight, and the temperature-rise budget in one place.

• • Closed-form trace fit in one screen: The Brooks-style empirical equation is built in, so a layout review no longer needs a separate handbook.
• • Internal and external layer support: Switching from external to internal halves k from 0.048 to 0.024, so the same calculator covers surface and buried traces.
• • Copper weight input covers common foils: 1 oz/ft² is the default; the input accepts 0.5, 1, 2, and 3 oz/ft² plus custom values from 0.25 to 6 oz/ft² for power planes.
• • Cross-section sanity check: The cross-section readout shows the geometric area used, so a typo in copper weight or temperature rise is visible.
• • Resistance and voltage drop together: The sized trace feeds an Ohm's law step, so resistance, voltage drop, and I²R power line up with the width.

The most useful output is usually the I²R power dissipation. Feed that number into a thermal model to see if the trace stays within the temperature-rise budget. For impedance-controlled layouts, run the calculator the other way and confirm the width is at least as large as the curve-fit minimum.

For pulsed or AC loads, the RMS to watts calculator converts the RMS voltage and current into the steady-state watts that drives the I²R power line.

Three variables drive the cross-section the closed-form fit returns, and two limitations tell you when to reach for a different tool.

• • The closed-form I = k × ΔT^0.44 × A^0.725 is an empirical curve fit. Real IPC-2152 correction-factor charts and detailed thermal simulations can differ from the fit by 10-20 % on tight budgets.
• • The width output assumes a flat rectangular trace. Plated half-ounces, selective gold plating, or unusual copper profiles change the effective cross-section.

These two limitations are also where the closed-form curve fit breaks down: tight temperature-rise budgets and non-rectangular cross-sections. For those cases, use a board-level thermal simulator or read the IPC-2152 correction-factor charts directly.

According to the UltraCAD Brooks & Adam thermal book page, the Brooks and Adam thermal simulations fit IPC-2152 external trace data closely and fit the internal trace data more closely than the older IPC-D-275 chart fit, which is why the calculator uses the closed-form equation for first-pass sizing.

When the I²R power dissipation needs to be reported in horsepower, BTU/h, or another unit, the power converter takes the watts number from the result panel and returns the same value in the unit the thermal report expects.