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Ground Rod Resistance and Test Calculator

Model an isolated vertical rod in homogeneous soil, explore a bounded target depth and compare actual tests with uncertainty and a chosen threshold.

Use this result well

Inputs that matter
Soil survey and geometry basis, Representative soil resistivity (ohm-m), Rod diameter (mm), Buried rod length to evaluate (m), and 6 more
Output to expect
Isolated vertical-rod resistance and depth model, Ground-test reading and uncertainty comparison
  • Check the units and required inputs before comparing results.
  • Keep the assumptions with a copied result so you can reproduce the calculation later.
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Reference & details

How it works

Isolated vertical-rod resistance and depth model

Explore the ideal resistance of one thin vertical rod in homogeneous soil, with its top at the surface. This uses measured representative soil resistivity, buried length and actual rod diameter. It does not determine how many electrodes are required or model layered soil, nearby electrodes, step/touch voltage or a complete grounding system.

Modified Dwight model: R = rho / (2πL) × [ln(8L/d) − 1], with rho in ohm-m and L,d in meters.

Ground-test reading and uncertainty comparison

Compare documented resistance readings plus their stated absolute uncertainty with a chosen review threshold. Each row is an independent measurement record. A numerical comparison does not establish that the test method measured the intended electrode or that the grounding system is compliant.

Upper comparison bound = reading ohms + absolute uncertainty ohms; compare each bound with the entered target.

Updated: September 2026

Example Scenarios

Try the built-in example, then replace its source data with your actual documented values. Retain failed comparisons and unresolved decisions.

→ 39.831826 ohms ideal isolated-rod resistance

Try the built-in example, then replace its source data with your actual documented values. Retain failed comparisons and unresolved decisions.

→ 1 recorded upper bounds exceed the target

FAQ

Explore the ideal resistance of one thin vertical rod in homogeneous soil, with its top at the surface. This uses measured representative soil resistivity, buried length and actual rod diameter. It does not determine how many electrodes are required or model layered soil, nearby electrodes, step/touch voltage or a complete grounding system. Compare documented resistance readings plus their stated absolute uncertainty with a chosen review threshold. Each row is an independent measurement record. A numerical comparison does not establish that the test method measured the intended electrode or that the grounding system is compliant.

Use the exact equipment, dimensions, current ratings, operating conditions and applicable requirements described in the selected mode. Unknown values are not replaced by a generic wire, device count or capacity. Illustrative examples are arithmetic examples, not an approved installation.

Save planning case keeps an explicit local history entry. Copy MD retains current inputs, source notes and interpretation; Download CSV exports the current result breakdown. Export a separate copy before changing devices or clearing browser storage.

About Ground Rod Resistance and Test Calculator

Explore the ideal resistance of one thin vertical rod in homogeneous soil, with its top at the surface. This uses measured representative soil resistivity, buried length and actual rod diameter. It does not determine how many electrodes are required or model layered soil, nearby electrodes, step/touch voltage or a complete grounding system. Compare documented resistance readings plus their stated absolute uncertainty with a chosen review threshold. Each row is an independent measurement record. A numerical comparison does not establish that the test method measured the intended electrode or that the grounding system is compliant.