Published: May 2026 | Reading time: ~10 min

2oz in Mils: How Thick Is 2 oz Copper on a Circuit Board?

2oz in mils means a 2 oz PCB copper layer is about 2.8 mils thick, or approximately 70 microns. In PCB manufacturing, “2 oz” does not mean the board weighs 2 ounces. It means the copper foil has a nominal mass of 2 ounces per square foot, which corresponds to a practical design thickness of about 0.0028 inches.

For engineers, PCB designers, and electronics manufacturing teams, this conversion matters because copper thickness affects trace resistance, current capacity, heat rise, etching limits, impedance control, and fabrication cost.

TL;DR / Key Takeaways

• 2 oz copper is approximately 2.8 mils thick, equal to about 70 microns.
• A mil is one-thousandth of an inch, so 2.8 mils equals 0.0028 inches.
• 1 oz copper is commonly treated as 1.37 mils, or about 35 microns.
• 2 oz copper reduces trace resistance compared with 1 oz copper but requires wider fabrication allowances.
• Use 2 oz copper for higher-current PCB traces, power electronics, and thermal spreading.

Table of Contents

• What Does 2oz in Mils Mean?
• 2 oz Copper Thickness Conversion Chart
• How Does Copper Weight Convert to Thickness?
• How Thick Is 2 oz Copper in Mils?
• 2 oz Copper vs 1 oz Copper
• Why Use 2 oz Copper PCB Material?
• How to Choose PCB Copper Weight
• Common Design Rules for 2 oz Copper PCBs
• Final Thoughts

What Does 2oz in Mils Mean?

In PCB design, 2oz in mils refers to the thickness of a copper layer made from 2 oz copper foil. The standard design shorthand is:

A mil is not a millimeter and is not a milliliter. A mil is 0.001 inch, which equals 25.4 microns. The inch-to-metric relationship is defined through SI unit practice by NIST.

This distinction is important because generic search results often interpret “2 oz in ml” as a fluid-volume question. In PCB manufacturing, the intended meaning is usually 2 oz copper thickness in mils, not fluid ounces converted to milliliters.

2 oz Copper Thickness Conversion Chart

The most useful answer for fabrication and design review is simple:

For quick engineering work, use 2.8 mils or 70 µm for 2 oz copper. For procurement, stackup notes, and fabrication release, confirm whether the value refers to base copper, finished copper, or copper after plating.

That distinction matters on outer PCB layers because electroplating can add copper during fabrication. Inner layers usually use copper foil thickness more directly, while outer layers may end up thicker after plating steps.

How Does Copper Weight Convert to Thickness?

PCB copper weight is specified as the mass of copper spread over one square foot of surface area. A 1 oz copper layer means 1 ounce of copper per square foot. A 2 oz copper layer means 2 ounces of copper per square foot.

The conversion follows this relationship:

Copper thickness = copper mass ÷ (copper density × surface area)

Copper has a density of about 8.96 g/cm³, and its room-temperature electrical resistivity is commonly cited near 1.724 × 10⁻⁸ Ω·m. These physical properties are published by the Copper Development Association.

Using the mass-per-area definition, 1 oz copper calculates close to 34–35 microns, depending on rounding conventions. Therefore, 2 oz copper is approximately 68–70 microns. PCB fabricators and designers typically round this to 70 µm, or 2.8 mils, for practical stackup and design-rule discussions.

How Thick Is 2 oz Copper in Mils?

2 oz copper is approximately 2.8 mils thick. Since 1 mil equals 0.001 inch, 2.8 mils equals 0.0028 inches. In metric units, that is approximately 0.070 mm, or 70 microns.

The mil conversion is:

70 µm ÷ 25.4 µm per mil = 2.76 mils

That result is usually rounded to 2.8 mils in PCB manufacturing. If a drawing lists 2 oz copper as 2.7 mils, 2.75 mils, or 2.8 mils, the values are typically referring to the same nominal copper class, not three meaningfully different materials.

For controlled-impedance boards, high-current traces, and power electronics PCBs, the exact finished copper thickness should still be confirmed with the fabricator. Standards such as IPC-2221 provide general design guidance, while fabrication capability depends on the board shop’s process limits.

2 oz Copper vs 1 oz Copper

The main difference between 2 oz copper and 1 oz copper is thickness. 1 oz copper is about 1.37 mils, while 2 oz copper is about 2.8 mils. That makes 2 oz copper roughly twice as thick.

Because resistance is inversely related to conductor cross-sectional area, doubling copper thickness can reduce trace resistance significantly when trace width stays the same. For example, a trace made with 2 oz copper has about 2× the copper cross-section of the same-width trace made with 1 oz copper.

That does not mean every PCB should use 2 oz copper. Thicker copper can make fine traces harder to etch cleanly. It may also require larger spacing, adjusted solder mask design, and a higher fabrication quote.

Why Use 2 oz Copper PCB Material?

Designers use 2 oz copper PCB material when the circuit needs more current capacity, lower voltage drop, or better heat spreading than standard 1 oz copper can provide.

Common use cases include:

• DC-DC converters
• Motor drivers
• Battery management systems
• LED lighting boards
• Power distribution PCBs
• Automotive and industrial control boards
• High-current connectors and relay outputs

A thicker copper layer gives each trace more cross-sectional area. That reduces resistance and can help control temperature rise. Trace current calculations are commonly based on IPC methods, but many modern designers reference IPC-2152 because it gives more detailed guidance on current, conductor geometry, board construction, and thermal environment than older simplified charts.

A practical example: if a board has a 100 mil wide power trace, switching from 1 oz copper to 2 oz copper roughly doubles the copper cross-section. That can lower I²R losses and improve voltage delivery, especially in compact power electronics layouts.

Is 2 oz Copper Worth It for PCB Fabrication?

2 oz copper is useful when the electrical or thermal benefit justifies the fabrication tradeoff. It is usually a good choice for high-current PCBs, but it can be unnecessary for low-current signal boards.

Use 2 oz copper when:

• Trace current is high enough that 1 oz copper requires very wide traces.
• Voltage drop across power paths must be reduced.
• The board carries heat away from power devices.
• Connectors, MOSFETs, inductors, or relays create concentrated current paths.
• The design has enough room for wider spacing and fabrication tolerances.

Avoid defaulting to 2 oz copper when:

• The PCB is mostly low-current digital logic.
• The design needs very fine pitch routing.
• Controlled impedance is easier to achieve with thinner copper.
• Cost and lead time matter more than current capacity.
• Thermal performance is already handled by planes, vias, heatsinks, or copper pours.

In many boards, a mixed approach is best: use 1 oz copper for dense signal routing and reserve thicker copper for power layers or specific high-current designs.

How to Choose PCB Copper Weight

Choosing PCB copper weight starts with current, temperature rise, voltage drop, and fabrication limits. The right value is not only a thickness decision; it is a system-level design choice.

A good workflow is:

1. Estimate current per trace or plane.
2. Define acceptable voltage drop.
3. Set maximum temperature rise.
4. Calculate trace width using IPC-based methods or a PCB trace width calculator.
5. Check whether the needed trace width fits the board.
6. Confirm minimum trace, spacing, and copper tolerance with the fabricator.

For early design estimates, 2 oz copper is a strong candidate when 1 oz copper forces traces to become too wide for the available board area. For final release, always use the fabricator’s process rules rather than a generic chart alone.

Internal reference suggestions:

• PCB trace width calculator
• PCB stackup design guide
• High-current PCB design rules

Common Design Rules for 2 oz Copper PCBs

2 oz copper PCBs need more design-rule attention than standard 1 oz boards. Thicker copper takes longer to etch, and etching tends to affect trace sidewalls as copper thickness increases.

Key design checks include:

• Minimum trace width: Ask the fabricator for 2 oz-specific limits, not only default 1 oz limits.
• Minimum spacing: Wider spacing may be required because thicker copper can increase etch variation.
• Solder mask clearance: Raised copper features can affect solder mask coverage.
• Plated holes: Finished hole size must account for copper plating thickness.
• Impedance control: Wider or adjusted geometries may be needed because copper thickness affects impedance.
• Copper balance: Large copper areas should be balanced to reduce bow, twist, and uneven plating.

Fabricators often separate base copper from finished copper. For example, a board may start with 1 oz base copper and receive additional copper plating on outer layers. Another board may specify 2 oz base copper before plating. These are not always equivalent, so procurement notes should be clear.

For production drawings, avoid writing only “2 oz copper” if the stackup needs tighter control. A clearer note is: “Outer layers: 2 oz finished copper. Inner layers: 1 oz base copper,” or the reverse, depending on the design.

Frequently Asked Questions

What is 2oz in mils?

2oz in mils means the approximate thickness of 2 oz PCB copper expressed in thousandths of an inch. In standard PCB shorthand, 2 oz copper is about 2.8 mils, equal to 0.0028 inches, 0.070 mm, or 70 microns.

How does copper weight convert to thickness?

Copper weight converts to thickness by dividing copper mass by copper density and surface area. PCB copper is specified in ounces per square foot. Since 1 oz copper is about 35 microns, 2 oz copper is about 70 microns, or 2.8 mils.

What is the thickness of 2 oz copper?

The thickness of 2 oz copper is typically treated as 70 microns, 0.070 mm, 0.0028 inches, or 2.8 mils. Exact values may vary slightly by foil class, plating process, and whether the specification means base copper or finished copper.

How many mils is 2 oz copper?

2 oz copper is about 2.8 mils thick. Using the metric conversion, 70 microns divided by 25.4 microns per mil equals approximately 2.76 mils, which PCB designers and fabricators commonly round to 2.8 mils.

Why use 2 oz copper PCB material?

Use 2 oz copper PCB material when a circuit needs higher current capacity, lower trace resistance, reduced voltage drop, or better heat spreading. It is common in power electronics, motor drivers, LED boards, battery circuits, and industrial control PCBs.

Final Thoughts

2oz in mils equals about 2.8 mils of PCB copper thickness, or roughly 70 microns. That conversion is the key number designers need when comparing 1 oz vs 2 oz copper, calculating trace width, or preparing a PCB stackup for fabrication.

For most low-current electronics, 1 oz copper is enough. For higher-current paths, compact power layouts, or boards where voltage drop and heat rise are design constraints, 2 oz copper can be the better engineering choice. The safest next step is to calculate trace width using your actual current and temperature-rise targets, then confirm copper thickness, spacing, and finished-copper requirements with your PCB fabricator.