Example 1: Find current through a resistor
If a circuit has 12 V applied across a 6 ohm resistor:
I = V / R = 12 / 6 = 2 A
The current through the resistor is 2 A.
Ohm's Law Calculator
Calculate voltage, current, or resistance by entering any two values.
Introduction
Ohm's Law is one of the most fundamental relationships in electrical and electronics engineering. It describes how voltage, current, and resistance are linked in a circuit and is widely used in troubleshooting, component selection, and circuit design. Whether you are checking a resistor, calculating current draw, or estimating a simple load voltage, Ohm's Law is often the first equation you need.
This calculator helps you quickly solve for the unknown electrical quantity when any two of the three basic values are known. It is useful for students, technicians, hobbyists, and engineers who need a fast answer without manually rearranging the equation each time.
Because so many other electrical checks depend on voltage, current, and resistance, this page is also a useful starting point before moving into power, voltage drop, or component selection calculations.
Formula
Voltage: V = I x R
Current: I = V / R
Resistance: R = V / I
Power: P = V x I
Current: I = V / R
Resistance: R = V / I
Power: P = V x I
Variable Definitions
V = voltage in volts
I = current in amperes
R = resistance in ohms
P = electrical power in watts
Units
Voltage is entered in volts, current in amperes, and resistance in ohms. The calculator returns the missing value in the same standard SI unit system, which makes it easy to move into related calculations such as power, voltage drop, and resistor selection.
Worked Examples
Example 2: Find equivalent resistance
If a load draws 5 A from a 230 V supply:
R = V / I = 230 / 5 = 46 ohm
The equivalent resistance is 46 ohm.
How To Interpret The Result
The main value of an Ohm's Law calculator is speed. In troubleshooting, you can move from a measured voltage and resistance to current immediately, or from measured current and voltage to an implied resistance. That can help you spot open circuits, overloaded loads, or values that do not match what a component or branch circuit should be doing under normal conditions.
It is also a foundation step for more advanced calculations. Once you know voltage, current, or resistance, you can move into power, voltage drop, wire sizing, or component selection with much more confidence. That is why Ohm's Law is one of the most reused relationships in both education and real electrical field work.
Practical Notes
Ohm's Law works well for linear components such as resistors and for many steady-state calculations. It is less direct for non-linear devices such as diodes and transistors, and AC circuits may require impedance instead of simple resistance. Even so, it remains one of the most useful quick-check tools in electrical work.
When using the result, always double-check the units. A value entered in milliamps instead of amps or kilo-ohms instead of ohms can change the answer by a factor of 1000. Good unit discipline is often the difference between a useful quick calculation and a misleading one.