Free Grounding Resistance Calculator
Estimate the ground resistance of a single vertical ground rod using soil resistivity.
ohm-m
m
mm
Ground Resistance
35.12 ohm
Ground Resistance vs Soil Resistivity (rho)
Ground Rod Resistance
The resistance of a ground rod depends on soil resistivity and rod geometry.
Formula (simplified for vertical rod)
R = (rho / 2 pi L) ln(4L / d)
where rho is soil resistivity in ohm-metres, L is rod length, d is rod diameter, and ln is the natural logarithm. Lower resistance is better for safety. Most codes require < 5 ohms for power systems and < 25 ohms for lightning protection.
Example Calculation
A 3 m x 16 mm ground rod in soil with 100 ohm-m resistivity.
- 01d = 0.016 m
- 02ln(4 x 3 / 0.016) = ln(750) = 6.62
- 03R = 100 / (2 x pi x 3) x 6.62 = 100/18.85 x 6.62 = 35.12 ohm
- 04This exceeds 5 ohm. Multiple rods or soil treatment may be needed.
Frequently Asked Questions
Learn More
Beam Stress Calculation Guide: From Theory to Practice
Learn how to calculate beam stress step by step. Covers bending stress, shear stress, the flexure formula, stress distributions, and practical design checks for structural beams.