# Ohm's Law and Power Triangle Calculator Solve for two unknowns among Voltage, Current, Resistance and Power from any two given values, with visual triangles and AC power-factor support > Canonical page: https://elysiatools.com/en/tools/ohms-law-calculator - **Category:** Math & Numbers - **Keywords:** ohms law, voltage, current, resistance, power, circuit, electrical, power triangle, cos phi, power factor, volts, amps, ohms, watts ## Overview Enter any two of V, I, R, P and the calculator derives the other two via Ohm's law (V=I·R) and power equations (P=V·I, P=I²·R, P=V²/R). AC mode applies P=V·I·cos φ and reports apparent power. Renders mnemonic Ohm's law and power triangles plus engineering SI units. ## Inputs - **Voltage (V, volts)** (number): e.g. 12 · leave blank if unknown - **Current (I, amps)** (number): e.g. 2 · leave blank if unknown - **Resistance (R, ohms)** (number): e.g. 6 · leave blank if unknown - **Power (P, watts)** (number): e.g. 24 · leave blank if unknown - **Mode** (select) - **Power Factor (cos φ)** (number): 0–1, e.g. 0.85 (AC only) ## When to use - When designing or troubleshooting electrical circuits and needing to quickly determine resistance, voltage drop, or current draw. - When calculating power dissipation in DC components or sizing resistors to prevent overheating. - When analyzing AC circuits with reactive loads, such as motors or transformers, requiring power factor (cos φ) adjustments. ## How it works - Enter any two known values among Voltage (V), Current (I), Resistance (R), or Power (P), leaving the other fields blank. - Select the circuit mode, choosing either DC (Direct Current) or AC (Alternating Current) with a specified Power Factor (cos φ). - The calculator solves the remaining two variables using Ohm's law and power equations, displaying the results with engineering SI units and visual mnemonic triangles. ## Use cases - Sizing a current-limiting resistor for an LED by calculating the required resistance based on target voltage drop and current. - Determining the current draw and apparent power of an AC electric motor using its rated wattage, voltage, and power factor. - Calculating the power dissipation of a heating element with a known resistance connected to a specific mains voltage. ## Frequently asked questions ### What is the minimum number of inputs required? You must enter exactly two known values out of Voltage, Current, Resistance, or Power to calculate the remaining two. ### How does the calculator handle AC circuits? In AC mode, the calculator incorporates the Power Factor (cos φ) into the power equation (P = V · I · cos φ) and reports the apparent power. ### What is the Power Factor (cos φ)? It is the ratio of real power to apparent power in an AC circuit, ranging from 0 to 1, representing how effectively electrical power is converted into useful work. ### Does the calculator support engineering units? Yes, the output displays values formatted with standard engineering SI prefixes such as kΩ, mA, and mW for easier reading. ### Can I calculate values for a three-phase AC system? 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