Earth electrode resistance calculator
Enter the soil resistivity and the electrode size. The calculator gives the resistance of a single rod, pipe or plate electrode and how many rods, well spaced, a target resistance needs.
Basis
IS 3043 (Code of practice for earthing): rod or pipe R = ρ / (2πL) · ln(4L / d); plate R = (ρ / 4) · √(π / A).
Reference values for planning and comparison. Confirm against the current standard, the purchaser’s specification and the manufacturer’s datasheet before ordering.
Single rod resistance (Ω) by soil resistivity
| Soil | 1.5 m × 40 mm | 3 m × 40 mm | 3 m × 17.2 mm |
|---|---|---|---|
| 10 Ω·m | 5.3 | 3 | 3.5 |
| 50 Ω·m | 26.6 | 15.1 | 17.4 |
| 100 Ω·m | 53.2 | 30.3 | 34.7 |
| 200 Ω·m | 106.3 | 60.5 | 69.5 |
| 500 Ω·m | 265.8 | 151.3 | 173.7 |
| 1000 Ω·m | 531.6 | 302.6 | 347.4 |
Worked example: 3 m pipe electrode in 50 Ω·m soil
- R = ρ ÷ (2π L) × ln(4L ÷ d) = 50 ÷ (2π × 3) × ln(12 ÷ 0.04).
- R = 15.1 Ω for one electrode.
- For 2 Ω, plan about 8 electrodes spaced at least 6 m apart, then measure.
What is the resistance of a 3 m earth rod?
In 100 Ω·m soil, a 3 m rod of 40 mm diameter is about 30.3 Ω by the IS 3043 formula. Halving resistivity halves the resistance.
How many earth pits are needed for 1 ohm?
Roughly the single-electrode resistance divided by the target, if electrodes are spaced at least twice their length apart. Closer spacing needs more electrodes because their fields overlap.
Does the calculator include the earth conductor?
No. Size the earthing conductor for the fault current with the short-circuit calculator, and measure the installed resistance on site.