Introduction
This trace width calculator helps you find the right copper trace size for your printed circuit board (PCB). It uses the IPC-2221 standard, which is the most common set of rules for PCB design. You enter your design current, copper thickness, and allowed temperature rise, and the tool gives you the minimum trace width needed for both external (in air) and internal (embedded) layers.
A trace that is too narrow can overheat and damage your board. A trace that is too wide wastes space. This calculator solves that problem by doing the math for you in seconds. It also shows resistance, voltage drop, and power loss if you enter a trace length. Every result includes a step-by-step solution, a chart, and clear diagrams so you can check the work and understand how the answer was found.
How to Use Our Trace Width Calculator
Enter your PCB design values below to find the minimum trace width needed for your external and internal copper layers. The calculator also shows resistance, voltage drop, and power loss when a trace length is provided.
Design Current (required): Enter the amount of current your trace must carry, in amps. This is the load current that will flow through the copper trace during normal use.
Copper Thickness (required): Enter the thickness of the copper on your PCB. You can pick oz/ft², mil, mm, or µm from the dropdown. Most standard boards use 1 oz or 2 oz copper.
Temperature Rise (required): Enter the maximum temperature increase you will allow above the ambient temperature. You can set this in °C or °F. A common starting point is 10 °C.
Ambient Temperature (optional): Enter the air temperature around your board. This value is shown with your results for reference but does not change the trace width calculation. The default is 25 °C.
Trace Length (optional): Enter the length of your copper trace. You can choose inches, feet, mil, mm, µm, cm, or meters. When you provide a length, the calculator will also show trace resistance, voltage drop, and power loss. Leave this field blank if you only need the trace width.
Click Calculate to see your results. Click Reset to return all fields to their default values. Click Copy Results to copy the full output to your clipboard.
What Is Trace Width and Why Does It Matter?
A trace is a thin strip of copper on a printed circuit board (PCB) that carries electric current from one part of the board to another. Think of it like a tiny wire, but flat and built right into the board. The trace width is how wide that copper strip is.
Getting the width right is important. If a trace is too narrow for the current it carries, it heats up. Too much heat can damage the board, melt solder, or cause the circuit to fail. A wider trace can carry more current without getting too hot. But making every trace extra wide wastes space on the board. That is why engineers calculate the exact width they need.
How This Trace Width Calculator Works
This calculator uses the IPC-2221 standard, which is the most widely accepted guideline in the electronics industry for PCB design. You enter three required values:
- Design current — how much current (in amps) the trace must carry.
- Copper thickness — how thick the copper layer is, usually measured in ounces per square foot (oz/ft²). One ounce equals about 1.378 mil (thousandths of an inch) of copper.
- Temperature rise — how many degrees the trace is allowed to heat up above the surrounding temperature.
From these inputs, the calculator finds the minimum trace width for both external layers (traces on the outside of the board, cooled by open air) and internal layers (traces buried inside the board, where heat escapes more slowly). Internal traces always need to be wider because they cannot cool as easily.
Optional Inputs: Trace Length and Ambient Temperature
You can also enter a trace length. When you do, the calculator shows three extra results: the trace's electrical resistance, the voltage drop across it, and the power loss as heat. These help you check whether your circuit will still work correctly after the small voltage loss along the trace.
Ambient temperature is the temperature of the air or environment around the board. It does not change the trace width calculation, but it helps you see the estimated maximum temperature the copper will reach during operation.
External vs. Internal Layers
PCBs often have multiple layers of copper stacked together. The top and bottom layers are called external layers. They sit in open air, so heat leaves them quickly. Layers sandwiched between sheets of fiberglass (FR-4) inside the board are called internal layers. Because the surrounding material traps heat, internal traces must be wider to stay within the same temperature rise limit. The IPC-2221 formula accounts for this by using a smaller constant (k = 0.024) for internal layers compared to external layers (k = 0.048).
Understanding the IPC-2221 Formula
The IPC-2221 formula first calculates the cross-sectional area of copper needed. It then divides that area by the copper thickness to get the trace width. The key equation is:
Area = (Current ÷ (k × ΔT0.44))1/0.725
Here, k is a constant that depends on whether the trace is external or internal, and ΔT is the allowed temperature rise in degrees Celsius. The result is an area in square mils. Dividing by the copper thickness in mils gives you the required width in mils.
This standard is based on charts and data that have been tested and trusted by engineers for decades. It gives safe, reliable results for most common PCB designs. However, if your current, temperature rise, or copper thickness falls outside the tested range, the calculator will warn you that results should be used with caution. For related electrical engineering calculations, you may also find our parallel resistor calculator, voltage divider calculator, and impedance calculator useful when designing your circuits.