Use this calculator for quick voltage-drop checks in resistive circuits and simple cable runs.
Inputs
This topic also has a deeper guide and a printable reference pack, so you can move from the live answer into the method, assumptions, and worked examples without leaving the topic cluster.
A denser practical sheet covering resistor combinations, divider outputs, LED resistor selection, voltage drop, and cable resistance in one workflow-oriented pack.
A practical field guide for low-voltage cable runs, voltage drop, line resistance, and quick sizing checks, designed for installation and bench planning rather than classroom-only use.
These are the main values the calculator uses. Keep the units consistent and, where relevant, match the assumptions explained in the related guide.
Unit: A
Use the current flowing through the same conductor or component whose resistance you are checking.
Unit: ohms
Enter the total resistance responsible for the drop, including any relevant conductor or loop estimate.
Use this page when you want a quick estimate of how much voltage is lost across a known resistance at a known current.
The main result is the voltage dropped across the resistance. The supporting figure shows how much power is being dissipated as heat in the same component or section of conductor.
If 2 A flows through 3 ohms, the voltage drop is 6 V and the power dissipated is 12 W.
This page assumes a simple resistive relationship. Real cable runs and components can vary with temperature, frequency, installation method, and tolerance.
No. It is a quick resistive estimate. Full cable design may also need installation factors, temperature, regulations, and allowable voltage-drop limits.
Estimate the resistance of a copper or aluminium conductor from its length and cross-sectional area.
Solve for voltage, current, or resistance from any two values and validate all three when you already have a full set of measurements.
Solve power, voltage, or current from the other two values using the core electrical power relationships.
Use the Current from Power Calculator for practical circuit and electronics work involving current from power.