Ohm's Law Calculator

Ohm's Law states that the current through a conductor between two points is directly proportional to the voltage across the two points, and inversely proportional to the resistance. The fundamental formula is V = I × R, where V is voltage (volts), I is current (amperes), and R is resistance (ohms).

Select 'Voltage' as what to solve for, then enter the known current (in amperes) and resistance (in ohms). The calculator instantly computes voltage using V = I × R.

Select 'Current' as what to solve for, then enter the known voltage (in volts) and resistance (in ohms). The calculator computes current using I = V / R.

Select 'Resistance' as what to solve for, then enter the known voltage (in volts) and current (in amperes). The calculator computes resistance using R = V / I.

Electrical power (P) is calculated using P = V × I (watts = volts × amperes). It can also be expressed as P = I² × R or P = V² / R. The tool calculates power automatically alongside the other values.

The calculator uses standard SI units: Voltage in Volts (V), Current in Amperes (A), Resistance in Ohms (Ω), and Power in Watts (W). For very large or very small values, results are displayed in scientific notation.

Ohm's Law is fundamental in electronics for selecting resistors, calculating LED current-limiting resistors, analyzing battery discharge rates, designing power supplies, troubleshooting circuits, and any scenario involving the relationship between voltage, current, and resistance.

Ohm's Law in its basic V = IR form applies directly to DC (direct current) circuits and resistive AC circuits. For AC circuits with capacitors and inductors, impedance (Z) replaces resistance (R), but the form V = I × Z still holds for magnitude calculations.

If resistance is zero, dividing voltage by zero is mathematically undefined (a short circuit). In practice, a short circuit allows infinite current, which is dangerous. The calculator will show an error if you attempt division by zero.

Ohm's Law is one of the most fundamental laws in electronics and electrical engineering. It allows engineers and hobbyists to predict how circuits will behave, choose appropriate components, ensure devices operate within safe limits, and troubleshoot malfunctioning circuits efficiently.

To find the current-limiting resistor for an LED: R = (Supply Voltage − LED Forward Voltage) / Desired LED Current. For example, with a 5V supply, 2V LED forward voltage, and 20mA current: R = (5 − 2) / 0.02 = 150 Ω. Use 'Resistance' mode and enter those values.

Voltage (V) is the electrical potential difference — the 'pressure' that drives electrons through a circuit, measured in volts. Current (I) is the actual flow of electrons through a conductor, measured in amperes (amps). Voltage is the cause; current is the effect (given resistance).