A copper weight to thickness calculator is an essential engineering tool used primarily in the manufacturing of Printed Circuit Boards (PCBs) and metal fabrication. Unlike standard measurements where thickness is measured directly in length units (like millimeters or inches), the PCB industry traditionally specifies copper thickness by its weight spread over a specific area—specifically, one ounce of copper rolled out to cover one square foot.
This unique unit of measurement, "ounces per square foot" (oz/ft²), often confuses newcomers to electronics design. This calculator bridges that gap by instantly converting the weight specification into tangible thickness dimensions such as mils (thousandths of an inch), micrometers (µm), and millimeters (mm).
Engineers, PCB designers, and fabrication managers use this tool to determine if a specific copper weight will support the required current density, manage thermal loads effectively, and fit within the mechanical constraints of the device enclosure.
Copper Weight Formula and Mathematical Explanation
The conversion from copper weight (oz) to thickness relies on the physical density of copper. The logic assumes a flat, uniform sheet of pure copper.
The Core Constants:
Density of Copper: Approximately 8.96 g/cm³ (or 8960 kg/m³).
1 oz (mass): Approximately 28.3495 grams.
1 ft² (area): Approximately 929.03 square centimeters.
The Derivation:
If you have 1 oz of copper spread over 1 ft², the thickness ($T$) is calculated by dividing the volume by the area.
$$ Volume = \frac{Mass}{Density} $$
$$ T = \frac{Volume}{Area} = \frac{Mass}{Density \times Area} $$
When you plug in the standard values for 1 oz copper:
Thickness ≈ 1.37 mils (thousandths of an inch)
Thickness ≈ 34.79 micrometers (µm)
Thickness ≈ 0.0348 millimeters (mm)
Variable Reference Table
Variable
Meaning
Unit
Typical Range
W
Copper Weight
oz/ft²
0.5 oz – 6 oz
T (mils)
Thickness
mils
0.7 – 8.2 mils
T (µm)
Thickness
micrometers
17 – 210 µm
ρ (rho)
Resistivity
Ω⋅m
1.68 × 10⁻⁸
Key variables used in copper thickness calculations.
Practical Examples (Real-World Use Cases)
Example 1: Standard Power Plane
Scenario: A PCB designer is creating a power distribution board and needs to know the physical thickness of a "2 oz copper" layer to check stack-up height constraints.
Input: 2 oz/ft²
Calculation: $2 \times 1.37 \text{ mils}$
Result: 2.74 mils (approx. 70 µm)
Interpretation: The layer adds roughly 0.07mm to the board's Z-axis height. This is standard for boards carrying moderate current (1-3 Amps) without excessive heating.
Example 2: Heavy Copper for Electric Vehicles
Scenario: An engineer designing a battery management system (BMS) for an EV specifies "4 oz copper" to handle high current surges.
Input: 4 oz/ft²
Calculation: $4 \times 34.79 \text{ µm}$
Result: ~139.16 µm (0.14 mm)
Interpretation: This thick layer provides lower resistance and better heat dissipation, crucial for the high-power environment of electric vehicles.
How to Use This Copper Weight to Thickness Calculator
Using this calculator is straightforward and designed for quick engineering checks.
Enter Copper Weight: Input the weight specification in ounces (oz). Common values are 0.5, 1, 2, or 3.
Optional Dimensions: If you want to calculate the total mass of a specific copper sheet or trace, enter the Width and Length in millimeters.
Review Results: The tool instantly displays thickness in three units: mils (Imperial), micrometers (Metric), and millimeters (Metric).
Analyze Extras: Check the "Total Weight" and estimated "Resistance" to understand the electrical and mechanical implications of your selection.
Compare: Use the chart to visually compare your input against standard industry weights.
Decision Guidance: If your calculated thickness is too thin for the required current (leading to overheating), consider increasing the copper weight (e.g., from 1 oz to 2 oz) or widening the trace.
Key Factors That Affect Copper Weight Selection
Choosing the right copper weight involves balancing electrical performance, cost, and manufacturability.
Current Carrying Capacity: Thicker copper (heavier weight) reduces resistance, allowing traces to carry more current with less temperature rise.
Thermal Management: Heavy copper acts as a heat spreader. 2 oz or 4 oz copper is often used in LED lighting or power supplies to dissipate heat effectively.
Impedance Control: For high-speed signals, the thickness of the copper affects the characteristic impedance of the transmission line. Changing from 1 oz to 0.5 oz may require adjusting trace width to maintain 50Ω impedance.
Etching Tolerances: Thicker copper requires more time in the etching bath, which can lead to "undercutting" (trapezoidal trace shapes). Fine-pitch components often require thinner copper (0.5 oz) for precise definition.
Cost: Heavier copper boards are more expensive due to higher raw material costs and more complex processing steps (lamination and etching).
Mechanical Flexibility: For flexible PCBs (Flex circuits), thinner copper (0.5 oz or roughly 17µm) is preferred to prevent cracking during bending.
Frequently Asked Questions (FAQ)
What is the thickness of 1 oz copper?
1 oz copper is approximately 1.37 mils (35 µm) thick. This is the industry standard for most signal layers in PCBs.
Why is copper measured in ounces instead of millimeters?
It is a historical tradition from the metal roofing and sheeting industry, referring to the weight of one square foot of material. It has persisted in the PCB industry as a shorthand standard.
When should I use 2 oz copper instead of 1 oz?
Use 2 oz copper for power planes, ground planes, or traces carrying higher currents (typically above 1-2 Amps) to minimize voltage drop and heat generation.
Is the thickness exact?
It is a nominal value. IPC standards allow for a tolerance of +/- 10% depending on the manufacturing class. Surface roughness can also affect the effective electrical thickness.
Does plating affect the final thickness?
Yes. The outer layers of a PCB are often plated with extra copper (typically 0.5 oz to 1 oz) to metalize the through-holes. A "1 oz finished" outer layer might start as 0.5 oz foil.
What is "Heavy Copper"?
Heavy copper usually refers to weights of 3 oz/ft² to 20 oz/ft². These are used for high-power distribution, battery chargers, and industrial controllers.
How does thickness affect resistance?
Resistance is inversely proportional to cross-sectional area. Doubling the thickness (e.g., 1 oz to 2 oz) halves the resistance per unit length, assuming the width remains constant.
Can I use this calculator for other metals?
No. This calculator uses the specific density of copper. Aluminum or gold would have different weight-to-thickness conversion factors.
Related Tools and Internal Resources
Explore more engineering calculators to optimize your electronics designs:
PCB Trace Width Calculator – Determine the required width for your specific current and temperature rise.
Via Current Calculator – Calculate how many vias you need to stitch planes together safely.
PCB Manufacturing Guide – A step-by-step look at how copper weight impacts the etching process.
Impedance Calculator – Design controlled impedance lines for high-speed signals.