Inputs and units
Use volts (V), amperes (A), ohms (Ω) and watts (W). Convert milliamps to amps before entering them: 250 mA is 0.25 A. Leave unknown values blank. If a pair gives an undefined result, such as nonzero power with zero resistance, the calculator asks you to check the inputs.
How the calculation works
V = I × R
P = V × I = I² × R = V² / RVoltage is the potential difference across the load. Current is the flow through it. Resistance links the two for an ohmic load, while power describes the rate of electrical energy transfer. Use values for the same component or circuit boundary; a supply voltage and the current through one branch do not describe every component in a parallel circuit.
Worked example
A resistive load connected to 12 V draws 2 A. Its resistance is 12 ÷ 2 = 6 Ω, and its power is 12 × 2 = 24 W. At that constant power, one hour uses 24 Wh, or 0.024 kWh. The calculator’s daily energy figure assumes the load stays on at that power for all 24 hours.
Assumptions and limits
Use this for steady DC or an ideal resistive AC load with consistent RMS values. Motors, transformers and other reactive AC loads need impedance and power factor; multiplying RMS volts by RMS amps gives apparent power, not necessarily real watts. LEDs, diodes and changing-temperature elements do not have one fixed resistance over all operating conditions. The result does not specify a safe conductor, fuse or component power rating.
References and calculation details
Page prepared September 18, 2026. Examples describe this calculator’s implementation; reference links do not imply independent certification.