Copper Weight to Thickness Calculator
Convert PCB copper weight (oz) into physical thickness (mils, microns, mm) instantly.
Calculated Thickness (Mils)
Figure 1: Visual comparison of calculated copper thickness against common objects.
What is a Copper Weight to Thickness Calculator?
A Copper Weight to Thickness Calculator is an essential engineering tool used primarily in the design and manufacturing of Printed Circuit Boards (PCBs). In the electronics industry, copper thickness is rarely specified by direct measurement (like millimeters or microns). Instead, it is specified by weight per area—specifically, how many ounces of copper are used to cover one square foot of substrate.
This calculator bridges the gap between the industry-standard "weight" specification (e.g., 1 oz copper) and the physical "thickness" needed for impedance calculations, stack-up planning, and thermal management. It is designed for PCB designers, electrical engineers, and hardware developers who need precise conversions to ensure their boards can handle the required current loads without overheating.
Who should use this tool?
- PCB Designers: To calculate stack-up height and clearance constraints.
- Electrical Engineers: To determine trace resistance and current carrying capacity.
- Hardware Enthusiasts: To understand the physical properties of the boards they are ordering.
Copper Weight to Thickness Formula and Explanation
The conversion from weight to thickness relies on the physical density of copper. Since "1 oz copper" actually means "1 ounce of copper spread over 1 square foot," we can derive the thickness using the volume and density relationship.
| Variable | Meaning | Unit | Standard Value |
|---|---|---|---|
| W | Weight of Copper | Ounces (oz) | Input Value |
| Area | Reference Area | Square Feet (ft²) | 1 ft² |
| ρ (Rho) | Density of Copper | g/cm³ | ~8.96 g/cm³ |
| T | Thickness | Mils / µm | Calculated Result |
Step-by-Step Derivation
1. Convert Units to Metric:
1 oz (avoirdupois) ≈ 28.3495 grams.
1 ft² ≈ 929.0304 cm².
2. Calculate Volume:
Since Density = Mass / Volume, then Volume = Mass / Density.
Volume = 28.3495 g / 8.96 g/cm³ ≈ 3.164 cm³.
3. Calculate Thickness:
Thickness = Volume / Area.
Thickness (cm) = 3.164 cm³ / 929.0304 cm² ≈ 0.003405 cm.
4. Convert to Mils and Microns:
0.003405 cm = 34.05 microns (µm).
34.05 µm / 25.4 ≈ 1.34 mils.
Note: In the industry, "1 oz copper" is nominally defined as 1.37 mils or roughly 35 microns due to slight variations in copper purity and manufacturing processes (rolled vs. electro-deposited).
Practical Examples (Real-World Use Cases)
Example 1: High-Current Power Supply Board
Scenario: You are designing a power supply unit (PSU) that needs to handle 20 Amps. You decide to use 2 oz copper to reduce resistance and heat. You need to know the thickness to calculate the required trace width.
- Input: 2.0 oz
- Calculation: 2.0 × 1.37 mils/oz
- Output: ~2.74 mils (69.6 µm)
- Interpretation: The copper layer is roughly twice as thick as a standard board, allowing for narrower traces for the same current, or cooler operation for the same width.
Example 2: Fine-Pitch BGA Breakout
Scenario: You are routing a complex FPGA with a fine-pitch Ball Grid Array (BGA). The manufacturer recommends 0.5 oz copper to allow for finer etching of traces between pads.
- Input: 0.5 oz
- Calculation: 0.5 × 1.37 mils/oz
- Output: ~0.69 mils (17.5 µm)
- Interpretation: The thinner copper foil allows the manufacturer to etch very thin traces (e.g., 3-4 mils wide) with higher precision than they could with 1 oz or 2 oz copper.
How to Use This Copper Weight to Thickness Calculator
- Enter Copper Weight: Locate the "Copper Weight (oz)" field. The default is 1.0 oz, which is the industry standard for most PCBs. Change this to match your specification (e.g., 0.5, 2, 3, or even 4 oz for heavy copper boards).
- Select Density (Optional): If you are using specialized copper (like rolled annealed), you can adjust the density. For 99% of cases, the default "Standard Copper" is correct.
- Review Results: The calculator updates instantly.
- Mils: Used primarily in the US and imperial-based design tools.
- Microns (µm): Used globally and in metric-based fabrication houses.
- Check the Chart: Look at the bar chart to visualize how thick the copper is compared to a standard sheet of paper or a human hair.
- Copy Data: Click "Copy Results" to paste the specifications into your design documentation or email.
Key Factors That Affect Copper Thickness Results
While the math is straightforward, real-world PCB manufacturing involves several factors that influence the final thickness of the copper on your board.
1. Manufacturing Tolerances
PCB fabrication is a chemical process. The IPC-6012 standard allows for tolerances in final copper thickness. A "1 oz" starting foil might end up slightly thinner after cleaning processes, or thicker if plating is added.
2. Plating vs. Base Foil
On outer layers, manufacturers start with a base foil (e.g., 0.5 oz) and then electroplate additional copper to plate the holes (vias). This plating adds thickness. A finished "1 oz" outer layer often starts as 0.5 oz foil + 0.5 oz plating.
3. Temperature Coefficients
While temperature doesn't change the amount of copper, it affects the resistance of that thickness. When calculating current capacity based on this thickness, you must account for the temperature rise allowed (e.g., +10°C or +20°C).
4. Copper Purity
Standard Electronic Grade (ED) copper is about 99.8% pure. Higher purity copper reduces resistance slightly but has similar density. Impurities can alter the mechanical strength and density slightly, affecting the weight-to-thickness ratio.
5. Surface Roughness
To get copper to stick to the FR-4 fiberglass, the copper surface is roughened. This "tooth" structure means the effective thickness for high-frequency signals (Skin Effect) might differ from the physical DC thickness measured by this calculator.
6. Etching Factors
During the etching process, acid eats away copper from the top down. Thicker copper (e.g., 3 oz) suffers from more "undercut" (trapezoidal trace shape) than thinner copper. This is why 0.5 oz is preferred for fine lines.
Frequently Asked Questions (FAQ)
The most common standard is 1 oz finished copper, which corresponds to approximately 1.37 mils or 35 microns. For inner layers, 0.5 oz (17.5 µm) is also very common.
It is a historical legacy from the roofing and sheeting industry, measuring the weight of copper rolled out to cover one square foot. It remains the standard unit in the PCB industry globally.
Heavy copper generally refers to weights of 3 oz (105 µm) or more. It is used for high-power distribution, battery management systems, and automotive electronics.
Thicker copper has a larger cross-sectional area, which lowers resistance. Lower resistance means less heat generation for a given current, allowing the trace to carry more power safely.
Not exactly. Mathematically, it is closer to 34.1 microns based on pure copper density, but industry convention often rounds it to 35 microns or uses a nominal 1.37 mils (34.8 microns).
Yes, the weight-to-thickness conversion is physical and applies to both. However, keep in mind that outer layers usually include plating thickness on top of the base foil.
You can, but manufacturers usually convert it back to the nearest ounce equivalent to select their foil stock. It's safer to specify in ounces to avoid ambiguity.
2 oz copper is approximately 2.74 mils or 70 microns thick.
Related Tools and Internal Resources
Explore more tools to assist with your electronics design and engineering projects:
- PCB Trace Width Calculator: Determine the required trace width for your specific current and copper thickness.
- Via Current Capacity Calculator: Calculate how much current a plated through-hole via can handle.
- PCB Impedance Calculator: Design controlled impedance traces for high-speed signals.
- Power Plane Resistance Calculator: Calculate the voltage drop across large copper areas.
- Skin Depth Calculator: Analyze AC resistance at high frequencies based on copper thickness.
- Voltage Drop Calculator: Ensure your power delivery network is efficient.