# Electronic – Calculate resistance of coil/inductor made of PCB traces

copperresistancetrace

This is to be a NFC coil/inductor of 1.1uH according do ST's eDesignSuite tool, with 7 turns.

The drawing above follows these parameters: ST's tool give inductance value as 1.1uH, but also I need to know the resistance of entire track, in ohms.
I have measured the antenna total lenght on the layout software and it is 418 mm long.

So I have these parameters:

• 0.25mm width
• 418mm length
• 0.5 oz (17.5 micrometers) copper thickness

Then I entered these value of this calculator: https://www.allaboutcircuits.com/tools/trace-resistance-calculator/

And the result given by the site is 1.66 Ohms. Can I trust this value? I need the know correct value of resistance to calculate the components of RF portion of NFC filter and matching circuits.

The board will have 0.5 oz copper thickness, I can guarantee this.

Resistivity of Annealed copper: 1.72x10-8 Ωm

Resistivity is defined as:

$$\ \rho = R\cdot \frac{A}{l}\$$

therefore $$\ R = \frac{\rho \cdot l}{A} \$$

your length is 0.418m your area is $$\0.25\,\mathrm{mm}\times 17.5\,\mu \mathrm{m}\$$

therefore your resistance = $$\ \frac{ 1.72\times10^{-8} \,\Omega \mathrm{m} \,\times\, 0.418\, \mathrm{m}}{ 0.25\,\mathrm{mm} \,\times\, 17.5\,\mu \mathrm{m}} = 1.64\,\Omega\$$ at 20C