How to Calculate for a Load Resistor

By David Gitonga

The load resistance can be calculated using Ohm's Law.
i electronic component board 1 image by PeteG from

Load resistance, also referred to as load impedance, is the opposition that an alternating current experiences on the device being fed the signal. A speaker offers load impedance to incoming signals. Load resistance is employed in a number of ways. It can be used to determine matching impedances as well as bridging impedances, each of which has a different application in electronic circuits. In most cases, however, a high load resistance is preferred, as it results in maximum voltage transfer.

Basic Circuits

Determine the total voltage in the circuit by adding all the voltage sources together.

Determine the total current in a circuit by adding each individual branch current in a parallel circuit. Current in a series circuit is the same, so only one current through one component is needed to determine the overall current in a circuit.

Use Ohm's Law to determine the total resistance. The following formula is used to determine the total resistance in a circuit when both current and voltage are known: R = V / I, where R = Resistance, V = Voltage, and I = Current.

Parallel Circuits

Calculate parallel resistances using the following formula: 1 / R = 1/R1 + 1/R2 + 1/R3 + 1/Rn. Rn represents the total number of load resistances in parallel.

Work out the resistances of identical resistors in a parallel circuit by taking the resistance of one of the resistors and dividing it by the number of resistors.

Use Ohm's Law to determine other values in the circuit using the total resistance that have been determined.

Add the resistances of both series and parallel circuits after computing the resistances of each circuit separately. Use the methods described in previous steps to determine the resistances of each network.