Engineering & Physics CalcyZone Calculator

Ohm's Law and Power Calculator

Calculate voltage, current, resistance, and electrical power with instant unit conversions.

Enter any two known electrical values. The remaining parameters will be calculated automatically.

Voltage (V - Volts)

Current (I - Amperes)

Resistance (R - Ohms Ω)

Power (P - Watts W)

Electrical Parameters Matrix

Voltage (V)12 V

Current (I)3 A

Resistance (R)4 Ω

Power (P)36 W

Mathematical Formula

V = I * R | P = V * I = I^2 * R = V^2 / R

Overview & Explanation

Ohm's Law states that electric current passing through a conductor between two points is directly proportional to voltage across the points.

How It Works

Voltage V = Current I * Resistance R
Power P = Voltage V * Current I = I² * R = V² / R
Provide any two known values to compute the remaining parameters.

Practical Applications

Designing electronic circuits and selecting resistor ratings.
Determining circuit power consumption and thermal heat dissipation.
Sizing electrical wires and circuit breakers for safe loads.

Ohm's law and power

Ohm's law states that the voltage across a resistor equals the current through it times its resistance: V = I × R. Knowing any two values gives the third: I = V ÷ R and R = V ÷ I. Electrical power links them too: P = V × I = I² × R = V² ÷ R.

Ohm's law holds for ordinary resistors at a steady temperature. Components such as LEDs, diodes and filament bulbs are non-linear, so their resistance changes with current.

Worked example

An LED needs 20 mA and drops 2 V, powered from a 5 V supply. The series resistor must drop 3 V, so R = 3 ÷ 0.020 = 150 Ω. It dissipates P = 3 × 0.020 = 0.06 W, so a standard 0.25 W resistor is fine. A 1,000 W kettle on 230 V draws I = 1,000 ÷ 230 = 4.35 A and has a resistance of about 52.9 Ω when hot.

Safety note

Choose resistors and wires rated well above the power and current you calculate, typically at least double, to stay cool and safe. Mains voltage is dangerous; leave household wiring work to a licensed electrician.