Copper Weight Converter
Convert copper thickness without confusing a nominal PCB copper grade with an exact mass-per-area calculation. Choose the basis explicitly.
35 µm per oz: linear nominal convention.
8.96 g/cm³: physical density assumption.
Choose the basis before converting.
A nominal ounce grade is not a measurement of finished copper. The two conversion modes intentionally give different results.
Nominal grade and physical thickness are different.
PCB copper grades are commonly specified using an ounce designation. Fabrication processes and the purchase specification determine the base and finished copper requirements. Manufacturing context
This tool offers a stated nominal convention and a separate mass-density calculation. It does not declare either result to be the minimum acceptable finished copper.
Nominal mode (declared linear convention): T [µm] = oz grade × 35 Physical mass-density mode: 1 avoirdupois oz = 28.349523125 g 1 international ft² = 0.09290304 m² Reference copper density = 8.96 g/cm³ Areal mass [g/m²] = oz/ft² × 28.349523125 / 0.09290304 T [µm] = areal mass [g/m²] / 8.96 Both modes: 1 mil = 25.4 µm
Why the two modes disagree
Under the specified density, exactly 1 oz/ft² gives approximately 34.0571 µm. The nominal mode returns 35 µm per oz grade by convention. The mass and length definitions are exact; the density is an assumed material property. Additional digits do not turn that assumption into a foil measurement. Unit definitions · Density reference
Fractional grades and finished copper
This nominal mode is explicitly linear: 0.5 oz grade maps to 17.5 µm. Suppliers may quote a half-ounce nominal foil as 17 or 18 µm and apply their own specified thickness tolerances. Check the approved foil / drawing specification. Plating and etching can change finished copper relative to starting foil.
| Ounce designation* | Nominal: 35 µm / oz grade | Physical: actual oz / ft² |
|---|---|---|
| 0.25 | 8.75 µm | 8.5143 µm |
| 0.5 | 17.5 µm | 17.0286 µm |
| 1 | 35 µm | 34.0571 µm |
| 2 | 70 µm | 68.1142 µm |
| 3 | 105 µm | 102.1713 µm |
| 4 | 140 µm | 136.2284 µm |
| 6 | 210 µm | 204.3427 µm |
Questions before
you use the result.
Know what the tool answers—and what still needs engineering review.
Why does physical mode show about 34.057 µm for 1 oz/ft²?
It divides the exactly converted areal mass by the stated 8.96 g/cm³ reference density. Nominal mode instead uses a declared 35 µm-per-oz-grade convention.
Is 0.5 oz always exactly 17.5 µm?
No. It is 17.5 µm only in this explicitly linear nominal convention. Suppliers may specify a rounded 17 or 18 µm nominal foil and separate tolerance limits.
Which copper thickness should I use for a trace calculation?
Use the finished thickness specified or measured for the actual layer, with the appropriate minimum and tolerance review—not an unqualified nominal grade.
Technical references & data basis
- NIST — SI and customary unit conversion factors
- Royal Society of Chemistry — copper density reference
- Würth Elektronik — BASIC Design Rules (PDF)
Check the linked manufacturer data and calculation references when using your results. Confirm the exact material grade and applicable document revision before production.