Copper Weight, Conversion & Fabrication Requirements
PCB Copper Thickness Capabilities
Convert copper weight into thickness, distinguish starting foil from finished copper and define the requirements for each PCB layer. PCBELEC supports outer-layer copper up to 15 oz and inner-layer copper up to 10 oz for specified board constructions.
- Unit Reference oz/ft² · μm · mm · mils
- Outer-Layer Copper Up to 15 oz/ft²
- Inner-Layer Copper Up to 10 oz/ft²
Copper Weight to μm, mm & mils
PCB Copper Weight to Thickness Conversion
Copper weight describes mass per unit area, commonly expressed in oz/ft². Copper thickness is a length. The chart below converts nominal copper weight into approximate thickness for PCB specification and design reference.
How Thick Is 1 oz PCB Copper?
≈ 35 μm · 0.035 mm · 1.37 mils
Common rounded values for 1 oz/ft² copper; nominal thickness is approximately 34.8 μm.
How Thick Is 2 oz PCB Copper?
≈ 70 μm · 0.070 mm · 2.74 mils
Common rounded values for 2 oz/ft² copper; nominal thickness is approximately 69.6 μm.
PCB Copper Thickness Conversion Chart
Swipe horizontally to view all thickness units.
| Copper Weight (oz/ft²) | Approx. μm | Approx. mm | Approx. mils |
|---|---|---|---|
| 1/3 oz | 11.6 | 0.0116 | 0.46 |
| 0.5 oz | 17.4 | 0.0174 | 0.69 |
| 1 oz | 34.8 | 0.0348 | 1.37 |
| 1.5 oz | 52.2 | 0.0522 | 2.06 |
| 2 oz | 69.6 | 0.0696 | 2.74 |
| 3 oz | 104.4 | 0.1044 | 4.11 |
| 4 oz | 139.2 | 0.1392 | 5.48 |
| 5 oz | 174.0 | 0.1740 | 6.85 |
| 6 oz | 208.8 | 0.2088 | 8.22 |
| 8 oz | 278.4 | 0.2784 | 10.96 |
| 10 oz | 348.0 | 0.3480 | 13.70 |
| 12 oz | 417.6 | 0.4176 | 16.44 |
| 15 oz | 522.0 | 0.5220 | 20.55 |
Values use approximately 34.8 μm per oz/ft² and are rounded. They are nominal conversions, not minimum finished-copper acceptance limits or a capability statement for every layer and board construction.
Use Copper Weight per Unit Area
In PCB specifications, “1 oz copper” is shorthand for 1 oz/ft². An ounce by itself is a mass and cannot be converted to millimeters without defining the area and material.
Quick Nominal Conversion
Use these approximations for reference, then specify the required manufacturing and acceptance basis separately. Thickness (μm) ≈ copper weight (oz/ft²) × 34.8 Copper weight (oz/ft²) ≈ thickness (μm) ÷ 34.8
Material Input vs. Finished Conductor
Starting Copper vs. Finished Copper
Starting copper identifies the foil used before circuit processing. Finished copper identifies the resulting conductor after the relevant fabrication steps. State which requirement applies to each layer instead of relying on a copper-weight label alone.
Illustrative Outer-Layer Conductor
Nominal Foil Is Not a Minimum Finished Value
A nominal copper-weight conversion describes an approximate material thickness. Manufacturing tolerances and processing mean it should not be used as an automatic finished acceptance limit.
Plating Does Not Create a Universal Formula
Outer-layer processing may add copper, while other steps remove copper. Do not assume a fixed starting-foil and plating combination without a defined manufacturing process.
Specify the Required Result
Identify controlled starting-foil requirements and any minimum finished conductor thickness separately. Include the layer, units, tolerance or applicable acceptance criteria.
Distinguish the Copper Requirements
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| Copper Definition | What It Describes | What to Specify |
|---|---|---|
| Starting copper foil | The copper foil used before the relevant conductor-processing steps. | Layer identity, nominal foil weight or thickness and any controlled material requirement. |
| Finished outer-layer copper | The outer conductor after relevant processing, including copper removal and any copper plating. | Finished-thickness requirement, minimum or nominal basis, units and applicable acceptance criteria. |
| Finished inner-layer copper | The internal conductor after its applicable circuit-processing steps. | Layer-specific foil requirements and any finished-copper acceptance limits needed by the design. |
| Plated-hole copper | The copper deposit on the walls of specified plated holes, separate from surface conductor copper. | Hole-wall copper requirement, relevant hole types and specified verification criteria. |
Layer-Specific Copper Manufacturing
Inner- and Outer-Layer Copper Capabilities
PCBELEC supports standard and heavy-copper PCB requirements, with outer-layer copper up to 15 oz/ft² and inner-layer copper up to 10 oz/ft². Define the copper specification by layer alongside the complete board construction.
- Outer-Layer Copper Up to 15 oz/ft² Identify the starting-foil basis and any required finished-conductor thickness in the fabrication notes.
- Inner-Layer Copper Up to 10 oz/ft² Assign the foil and finished-copper requirements to the designated internal conductive layers.
- Stackup Definition Different Copper by Layer Plan heavier power layers and other routing layers within one released stackup.
Copper Configuration and Specification Basis
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| Copper Configuration | Capability / Reference | Define in Your Files |
|---|---|---|
| Standard copper selections | Common nominal references include 0.5 oz, 1 oz and 2 oz/ft². | State which layers use each selection and whether the note controls starting foil, finished copper or both. |
| Heavy outer-layer copper | Outer-layer capability up to 15 oz/ft². | Identify each outer layer, the copper requirement, critical conductor geometry and finished acceptance basis. |
| Heavy inner-layer copper | Inner-layer capability up to 10 oz/ft². | Release the inner-layer copper, dielectric construction and any required finished-thickness limits in the stackup. |
| Mixed copper weights by layer | Different copper requirements assigned to different conductive layers. | List the requirement for every layer and review copper balance, dielectric fill and conductor rules as one construction. |
| Minimum finished conductor copper | A separately defined acceptance requirement, not a nominal conversion. | Give the minimum value, units, applicable layer and relevant verification or acceptance criteria. |
| Plated-hole copper | Specified independently from surface copper weight. | Identify hole types, hole-wall copper requirements and any associated inspection criteria. |
Capability maxima do not imply that every copper weight, layer count and feature combination uses the same process. Mixed copper weights here means differences between layers, not different copper thicknesses within one layer.
Electrical Needs & Manufacturing Trade-Offs
Choosing Copper Weight for Your PCB
Choose copper from the required conductor geometry, electrical performance and board construction. More copper can reduce conductor resistance, but it also changes the layout and fabrication requirements.
1 oz vs. 2 oz Copper: What Changes?
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| Comparison Factor | 1 oz Copper Reference | Changing to 2 oz Copper |
|---|---|---|
| Nominal thickness | Approximately 34.8 μm, commonly rounded to 35 μm. | Approximately 69.6 μm, commonly rounded to 70 μm. |
| Conductor cross-section | Defined by the actual finished thickness and conductor width. | Approximately doubles if actual finished thickness doubles and the conductor width stays the same. |
| DC conductor resistance | Depends on length, cross-section, material and temperature. | Approximately halves for the same length, width, material and temperature if finished thickness doubles. |
| Allowable current | Requires a defined temperature-rise and operating-condition assessment. | Does not automatically double. Reassess the conductor and complete thermal environment. |
| Trace and spacing rules | Use rules matched to the actual copper and fabrication process. | Review etch compensation, finished widths and available spacing before retaining the original layout. |
| Stackup and fabrication | Copper is one part of the complete board definition. | Review dielectric fill, copper balance, mask coverage and any controlled-impedance geometry. |
Electrical comparisons are simplified and assume the stated conditions. Nominal foil labels alone do not establish the exact finished cross-section or an application current rating.
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Define the Electrical Requirement
Identify continuous and peak current, duty cycle, allowable voltage drop and temperature rise. Evaluate bottlenecks such as neck-downs, terminals and interlayer connections as well as the main copper path.
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Compare Copper Thickness with Available Width
Review the available routing area before increasing copper weight. Wider conductors, planes or suitable parallel paths may form part of the design, with their connections and current sharing assessed together.
-
Check the Whole Stackup
Assign copper requirements to the relevant layers. Review layer position, dielectric construction, copper distribution and any impedance-controlled structures instead of increasing every layer by default.
-
Review Manufacturing Before Design Release
Check conductor spacing, hole structures, resin fill and solder-mask coverage against the selected copper. Include the required finished-copper basis and critical no-change features in the fabrication package.
Three Different Thickness Specifications
Copper Thickness, Copper Core and Board Thickness
Circuit copper, the copper base and the finished PCB thickness describe different parts of a board. Define each applicable requirement separately instead of using one thickness value for all three.
Illustrative Insulated Copper-Base Cross-Section
- Circuit copper
- Dielectric
- Copper base
Conductor Copper Thickness
The thickness of a conductive circuit layer. Specify it by layer using copper weight or thickness units, with the starting or finished requirement clearly identified.
Copper Core / Base Thickness
The thickness of the copper metal core or base in the specified construction. It is a separate structural requirement, not a substitute for circuit copper weight.
Finished PCB Thickness
The overall finished-board dimension at the specified measurement location. State the tolerance and whether coatings or finishes are included in the drawing's measurement basis.
Need Thicker Circuit Conductors?
Explore heavy-copper fabrication for layer-specific conductor requirements, copper-related DFM and prototype-to-production manufacturing.
Heavy Copper PCB FabricationNeed a Copper-Base Construction?
Explore the copper-core service for the required base structure. Define circuit copper, dielectric and metal-base requirements together.
Copper Core PCB ManufacturingStackup Notes & Manufacturing Definition
How to Specify Copper in Your Fabrication Files
Place copper requirements in the released stackup or fabrication drawing. Use matching layer names, clear units and an explicit starting or finished basis so the intended conductor requirement is carried into manufacturing.
Identify Each Layer or Feature
Match copper notes to the layer names in the artwork and stackup. Identify plated-hole requirements separately from circuit-layer copper.
State the Requirement and Units
Distinguish nominal starting foil from minimum finished copper. Use oz/ft², μm or other explicit units and state the applicable tolerance or acceptance basis.
Include the Complete Construction
Provide layer order, material, dielectric requirements and finished board thickness. For copper-base builds, define the metal base independently of the circuit copper.
Keep the Release Consistent
Use one matching revision across the artwork, drawing and stackup. Identify open items and resolve conflicting copper notes before the manufacturing definition is released.
Submit copper notes together with the board files, quantity and required delivery date.
Conversion & Specification Questions
PCB Copper Thickness FAQ
Answers to common questions about copper-weight conversion, finished copper and layer-specific fabrication requirements.
Preparing manufacturing files? Identify the copper requirement and acceptance basis for each relevant layer or feature.
View the Specification TemplateHow thick is 1 oz copper in mm, microns and mils?
One ounce per square foot of copper is approximately 34.8 μm, 0.0348 mm or 1.37 mils. It is commonly rounded to 35 μm or 0.035 mm in PCB discussions.
These are nominal equivalents. They do not automatically define the minimum finished copper accepted on a manufactured board.
How thick is 2 oz copper?
Two ounces per square foot of copper is approximately 69.6 μm, 0.0696 mm or 2.74 mils. Common rounded values are 70 μm and 0.070 mm.
State whether the requirement refers to starting foil or finished conductor copper when preparing the fabrication specification.
Can ounces be converted directly to millimeters?
Not without additional information. An ounce is a mass, while a millimeter is a length. PCB copper conversion uses mass per unit area, typically oz/ft², together with the density of copper.
In this context, “1 oz copper” means 1 oz/ft², not the total copper mass of the PCB. A mil is also a length unit: 1 mil equals 0.001 inch or 0.0254 mm.
Is nominal foil thickness the same as minimum finished copper?
No. Nominal foil describes the starting material reference. Finished copper reflects the conductor after the relevant fabrication processes.
Specify the required minimum finished thickness separately where it is a controlled design requirement, including the layer, units and acceptance criteria.
Does 1 oz copper on two layers make a 2 oz PCB?
It does not make either conductor layer 2 oz. The board has two separately specified 1 oz layers. Adding the layer weights does not replace the individual conductor requirements.
Define each layer in the stackup. Finished board thickness is a separate overall dimension.
What are the thickness equivalents of 16 oz and 20 oz copper?
Using the nominal reference of approximately 34.8 μm per oz/ft², 16 oz is about 556.8 μm or 0.5568 mm, and 20 oz is about 696 μm or 0.696 mm.
These are unit conversions, not supply-capability claims. This page lists PCBELEC outer-layer copper up to 15 oz/ft² and inner-layer copper up to 10 oz/ft².
Can copper thickness alone determine a safe current rating?
No. Conductor width and length, layer position, surrounding copper, allowable voltage drop, temperature rise and operating conditions all influence the design.
Assess the complete current path, including connections and vias. A copper-weight label is not a substitute for electrical and thermal validation of the application.
Can different PCB layers use different copper weights?
Yes. Assign the required copper to each power or routing layer in the stackup. Review the combination with the dielectric, copper balance, conductor rules and finished board requirements.
Different copper weights between layers do not mean different thicknesses within the same layer. Define any special same-layer construction explicitly.