Ohm's Law Calculator
Calculate voltage, current, resistance, and power using Ohm's Law with our free online calculator. Enter any two values to find the remaining electrical properties instantly.
About This Calculator
Our Ohm's Law Calculator helps you compute voltage, current, resistance, and power in electrical circuits. Whether you are an electrician, electronics hobbyist, engineering student, or DIY enthusiast, this tool simplifies your electrical calculations by instantly computing the missing values when you enter any two known parameters.
The calculator is based on the fundamental Ohm's Law formula V = I × R (voltage equals current multiplied by resistance) and the power formula P = V × I (power equals voltage multiplied by current). Simply enter any two of the three primary values — voltage in volts (V), current in amperes (A), or resistance in ohms (Ω) — and the calculator will determine the remaining values plus power dissipation in watts (W).
Ohm's Law is named after German physicist Georg Ohm, who first published his theory in 1827. It is one of the most fundamental principles in electrical engineering and is used extensively in circuit design, component selection, safety calculations, and troubleshooting. The law applies to ohmic conductors where resistance remains constant under fixed temperature conditions.
This calculator uses the standard SI units recognized globally, making it suitable for users in India, the United States, the United Kingdom, and anywhere in the world. For region-specific mains voltages, common values are 230V in the UK and India, and 120V in the US.
Frequently Asked Questions
What is Ohm's Law?
Ohm's Law states that the current flowing through a conductor is directly proportional to the voltage across it, provided the temperature remains constant. The fundamental formula is V = I × R, where V is voltage in volts, I is current in amperes, and R is resistance in ohms.
How do I calculate power using Ohm's Law?
Power is calculated using the formula P = V × I, where P is power in watts, V is voltage in volts, and I is current in amperes. You can also use P = I² × R or P = V² / R, depending on which two values you know.
What are the three formulas of Ohm's Law?
The three key formulas derived from Ohm's Law are: V = I × R (voltage equals current times resistance), I = V / R (current equals voltage divided by resistance), and R = V / I (resistance equals voltage divided by current).
Does Ohm's Law apply to AC circuits?
Yes, Ohm's Law applies to AC circuits, but with impedance (Z) replacing resistance (R). In AC circuits with reactive components like capacitors and inductors, the formula becomes V = I × Z, where Z accounts for both resistance and reactance.
What units are used in Ohm's Law calculations?
In Ohm's Law, voltage is measured in volts (V), current in amperes (A), resistance in ohms (Ω), and power in watts (W). These SI units are used universally across all countries including India, the US, and the UK.
Why is Ohm's Law important in electrical engineering?
Ohm's Law is fundamental to electrical engineering because it allows engineers to calculate voltage, current, resistance, and power in circuits. It is essential for circuit design, component selection, safety analysis, and troubleshooting electrical systems.
Can Ohm's Law be used for any material?
No, Ohm's Law only applies to ohmic materials such as metals and ceramics where the resistance remains constant regardless of voltage and current. Non-ohmic materials like semiconductors and insulators have non-linear voltage-current relationships and do not follow Ohm's Law.
What is the difference between Ohm's Law and Kirchhoff's Laws?
Ohm's Law relates voltage, current, and resistance within a single circuit element. Kirchhoff's Current Law (KCL) states that the sum of currents entering a node equals zero, and Kirchhoff's Voltage Law (KVL) states that the sum of voltages around a closed loop equals zero. Both are used together to analyze complex circuits.