Resistor Calculator
Calculate resistance using Ohm's Law R = V/I. Enter voltage and current to find resistance in ohms. Free online resistor calculator with charts for electronics.
About This Calculator
The Resistor Calculator helps you calculate resistance using Ohm's Law, one of the most fundamental principles in electronics and electrical engineering. Whether you are a student learning about circuits, a hobbyist building electronics projects, or a professional engineer designing electrical systems, this tool makes it easy to find resistance values from known voltage and current measurements.
Ohm's Law states that the resistance of a conductor is equal to the voltage across it divided by the current flowing through it: R = V / I. Resistance is measured in ohms (Ω), voltage in volts (V), and current in amperes (A). The calculator also shows a breakdown of your input values alongside the computed resistance, making it ideal for verifying circuit designs and troubleshooting electronic components.
This calculator is useful for determining resistor values in DC circuits, verifying component specifications, sizing resistors for LED circuits, calculating load resistance in power supply designs, and educational purposes in physics and electronics classrooms. For AC circuits with reactive components, impedance calculations that include inductive and capacitive reactance should be used instead.
Frequently Asked Questions
How does the Resistor Calculator work?
The Resistor Calculator uses Ohm's Law (R = V/I) to compute resistance. Enter the voltage across a resistor and the current flowing through it, and the calculator instantly returns the resistance in ohms using the standard formula.
What is Ohm's Law and how is it used in resistor calculation?
Ohm's Law states that the current through a conductor between two points is directly proportional to the voltage across the points. The formula R = V/I defines resistance, where R is resistance in ohms, V is voltage in volts, and I is current in amperes. This fundamental law is used in all electronics and electrical engineering applications.
What units does the Resistor Calculator use?
The calculator accepts voltage in volts (V) and current in amperes (A), and returns resistance in ohms (Ω). You can enter decimal values for precise measurements, such as 0.5 A or 12.6 V.
Is the Resistor Calculator free to use?
Yes, the Resistor Calculator is completely free to use with no registration or account required. You can calculate as many values as you need and share your results via URL.
Can I use this calculator for AC circuits?
This calculator uses Ohm's Law which applies to DC circuits and resistive AC circuits where the load is purely resistive. For AC circuits with inductive or capacitive components, impedance calculations that account for reactance are needed.
What is a typical voltage and current for household electronics?
Household voltages vary by region: 120 V in the US and Canada, 230 V in the UK and Europe, and 230 V in India. Typical currents range from 0.1 A for small devices to 10 A for high-power appliances. Always verify your local electrical standards before making calculations.
How do I share my resistor calculation results?
The calculator automatically saves your input values in the URL. You can copy the URL from your browser's address bar and share it with anyone. When they open the link, the inputs will be pre-filled and the calculation will run automatically.