![[Equation to find dc resistance from cross sectional area]](../images/round-wire-resistance-formula1.svg "Resistance from area"){kind=small}
Equation 1.Calculates the dc Resistance of a single round wire of common conducting materials using Equation 2 below.
Note: To use different values for the Resistivity, select Enter Data in the Conductor Material selection text box and then enter the required Resistivity (ρ) value in the box highlighted in amber.
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The dc resistance of a conductor is calculated using the resistivity and the cross-sectional area:-
Equation 1.
Where:
ρ is the Resistivity of the conductor in Ω.m
l is the Length in metres
A is the Cross-sectional area in metres
Round wire is normally specified by diameter and the dc resistance from the diameter is:-
![[Equation to find dc resistance from diameter]](../images/round-wire-resistance-formula2.svg "Resistance from diameter")
Equation 2.
Where:
ρ is the Resistivity of the conductor in Ω.m
l is the Length in metres
d is the diameter of the round conductor in metres
The values for ρ are from CRC Handbook of Chemistry and Physics 1st Student Edition 1998 page F-88 and are for high purity elements at 20°C.
| Table of "bench mark" measurements made in our lab using Enamelled Copper Wire | |||||
| Measured | Calculated | ||||
| Diameter | Length | Voltage | Current | Resistance | Resistance |
| (mm) | (mm) | (V) | (A) | (Ω) | (Ω) |
| 1.0 | 410 | 0.0091 | 1.031 | 0.008826 | 0.0087596 |
| 0.5 | 410 | 0.0359 | 1.031 | 0.03482 | 0.0350385 |
| 0.2 | 410 | 0.24 | 1.032 | 0.2326 | 0.2189908 |
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