# What is the mathematical formula for calculating the resistance-to-ground of parallel electrodes?

## We highly recommend using a computer program such as CDEGS to facilitate the calculation process.

**Slamat Asked:**What is the mathematical formula for calculating the resistance-to-ground of parallel electrodes?

**Our Answer:**The simplified calculation for predicting the resistance-to-ground (earth) of a given length grounding rod is:

**R=(p/(2*pi*L))*(ln*(4L/a)-1)) + (p/(2*pi*s))*(1-(L squared/3s(10X8)) + (2L(10×4)/5s(10×4)…)**

Where:

- R= Resistance
- p= soil resistivity
- L = Length of the rod
- a= radius of the rod
- ln= natural log
- s = rod spacing

The above is the hand formula, however it does not take into account multi-layered soils. We highly recommend using a computer program such as CDEGS.

**The Engineering Experts at E&S Grounding Solutions**