Earthing Resistance Calculator | Earth Rod & Soil Resistivity

Soil & Rod Parameters

Soil Resistivity (ρ)

(Typical: 10-100 Ω·m Garden/Clay, 1000+ Rock)

Rod Length (L)

m

Rod Diameter (d)

mm

Multiple Rods (Parallel)

Number of Rods (N)

Group Arrangement

Approximates mutual resistance effects.

Resistance Estimates

Single Rod (R₁) - Ω

Total System (R_t) - Ω

Status Check CHECK

*Based on BS 7430 simplified formulas. Always verify with field measurements (Fall-of-Potential method).

Technical Notes & Engineering Logic

Variable Definitions

ρ (Rho): Soil Resistivity (Ohm-meters). High variability based on moisture/salt.
L: Length of the rod buried in soil (meters).
d: Diameter of the rod (mm).
N: Number of parallel rods connected to the same earthing system.

Formulas (BS 7430)

Single Rod: R = (ρ / 2πL) × [ln(8L/d) - 1]
Group (Approx): R_t = (R₁ / N) × Factor
Factor accounts for mutual resistance when rods are close (typically Spacing = Length).

Assumptions

Soil is homogeneous (uniform resistivity).
Rod is driven vertically and fully buried.
"Auto" multiplier assumes rod spacing ≈ rod length (common practice).