Grounding Resistance Calculator
Use this grounding resistance workflow for early engineering screening when soil resistivity and rod geometry are known. It is not a field test or acceptance decision.
- Single-rod resistance
- ohm
- Estimated combined resistance
- ohm
- Spacing ratio
- x rod length
- Spacing effectiveness
- x
- Effective rod count
- count
Calculation details
- Calculation basis
- Selection boundary
Recent results
Formulas
- Rod length meters = rod length ft x 0.3048
- Rod diameter meters = rod diameter in x 0.0254
- Single rod resistance = soil resistivity / (2 x pi x rod length meters) x (ln(8 x rod length meters / rod diameter meters) - 1)
- Spacing ratio = rod spacing ft / rod length ft
- Effective rod count = 1 + (rod count - 1) x capped spacing effectiveness
- Estimated combined resistance = single rod resistance / effective rod count
Use this calculator
Estimate single-rod resistance, combined resistance, spacing ratio, spacing effectiveness, and effective rod count from entered soil and rod assumptions.
Read the result
Review the calculated values with their displayed units and assumptions. The result is a planning aid for the stated inputs, not a final equipment or installation decision.
Check before final work
This grounding resistance estimate is a simplified engineering approximation. It does not replace fall-of-potential testing, soil modeling, electrode design, bonding review, utility rules, AHJ requirements, or code compliance.
FAQs
Is this a ground resistance test result?
No. It is a model estimate from entered assumptions. Field testing and interpretation are separate tasks.
Why is spacing only an approximation?
Ground rod interaction depends on soil layers, electrode geometry, moisture, and installation details. This calculator only applies a capped screening factor.
Can this decide whether grounding is acceptable?
No. Acceptance criteria and electrode design require local code, AHJ, utility, and engineering review.