How to calculate the resistance?

Resistance (R) – physical quantity that characterizes the ability of a circuit element or section to prevent an electric current from flowing through it. Depending on the type of material, it may tend towards zero (conductors, semiconductors) or take huge values (dielectrics). The international unit of measure is Ohm (Ω).

This tool helps you calculate the resistance for a section of DC network by voltage, current and power, and also allows you to calculate active and reactive (inductive, capacitive) resistances for AC networks.

To calculate the resistance of a cable, you need to specify its length, cross-sectional area and specific material resistance, the remaining fields are cleared (active resistance = conductor resistance). The theoretical justification is presented below. Calculation results are updated after pressing the "Calculate" button.

Resistance calculation formulas

— Resistance through amperage and voltage: R = U / I
— Resistance through amperage and power: R = P / I²
— Resistance through voltage and power: R = U² / P

I – amperage, A;
U – voltage, V;
P – power, W.

— AC resistance (total): Z = √(R² + (X_L - X_C)²)
— Active resistance : R = (ρ × l) / S
— Inductive resistance: X_L = 2π × ƒ × L
— Capacitive resistance: X_C = 1 / (2π × ƒ × C)

ƒ – frequency, Hz;
L – inductance, H;
C – capacitance, F;
ρ – conductor resistivity, Ω·mm²/m;
l – conductor length, m;
S – conductor cross-sectional area, mm².