Calculate loop resistance, resistivity, length or cross-sectional area from any three values, or estimate resistance from AWG wire size and material.

Uniform conductor, DC resistance. Material presets assume 20ยฐC; joints, temperature changes and AC/fault-loop impedance are excluded.

For a loop, total path includes outgoing and return conductors.

Material preset (editable)

Selecting a material fills resistivity; you can edit it.

Loop Resistance Formula

The following formula is used to calculate the loop resistance for a given resistivity, total conductor path length, and cross-sectional area. For two identical outgoing and return wires, total path length is twice the one-way cable distance.

R = (ฯ ร— L) / A

Variables:

  • R is the loop resistance
  • ฯ is the resistivity in ฮฉยทm at the conductor temperature
  • L is the total conductor path length in metres, including outgoing and return conductors for a loop
  • A is one conductorโ€™s cross-sectional area in mยฒ

To calculate the loop resistance, multiply the resistivity by the length and divide by the cross-sectional area. This estimates uniform DC conductor resistance; it excludes connections and AC or earth-fault loop impedance. Material presets use approximate 20ยฐC values from OpenStax. AWG estimates use nominal equivalent solid-round area.

What is Loop Resistance?

Loop resistance is the total resistance encountered by an electrical current as it travels through a loop of conductive material. This resistance is influenced by the material’s resistivity, the length of the loop, and the cross-sectional area of the conductor. Loop resistance is a critical factor in the design and performance of electrical circuits, as it affects the efficiency and heat generation within the system.

How to Calculate Loop Resistance?

The following steps outline how to calculate the Loop Resistance.

  1. First, determine the resistivity of the material (ฯ).
  2. Next, measure the total conductor length (L), or choose the two-wire convention and enter one-way cable distance.
  3. Next, measure the cross-sectional area of the conductor (A).
  4. Finally, calculate the loop resistance using the formula R = (ฯ * L) / A.
  5. After inserting the values and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

Resistivity (ฯ) = 1.68 x 10^-8 ฮฉยทm

Total conductor path length (L) = 10 m (5 m out and 5 m return)

Cross-sectional Area (A) = 2 x 10^-6 mยฒ. Resistance = 0.084 ฮฉ.