Enter your values below for an instant estimate. Each calculator shows the formula it uses, so you can check the working yourself.
Diameter has a much smaller effect on resistance than length — doubling the rod length reduces resistance far more than doubling its diameter. In low-resistivity (highly corrosive) soils, don't reduce electrode diameter below 14–17 mm, as it affects service life more than performance.
This is a preliminary single-electrode estimate. Multi-rod arrays, mutual resistance between electrodes, and seasonal soil moisture variation are not accounted for — confirm with a fall-of-potential test on site.
Short-circuit impedance is set by the transformer designer, typically 4–6%. A lower impedance means lower losses but a higher fault current — sometimes high enough that it becomes expensive to clear safely through the earthing system.
If an earth resistance value is entered, EPR = I_fault × R. This voltage rise must stay within the step and touch voltage limits for the installation.
Increasing the spacing a probes deeper soil layers, building a picture of resistivity at depth. Most soils have two or three layers — a full multi-layer study needs dedicated software, but this two-layer estimate is a solid starting point.
Take readings at several spacings and average them; a single reading can be skewed by local variation near the electrodes.
Preliminary engineering estimates only, provided for design guidance. Actual earthing performance depends on soil conditions, moisture, and seasonal variation — confirm with on-site testing before finalising an installation. Reference: IS 3043 (Code of Practice for Earthing).