# Guide to the electricity calculators

The electricity calculators work with power, voltage, current and resistance: the power of a three-phase motor, Ohm's law and Watt's law, and what a household appliance costs to run.

## Electricity

### [3-Phase Motor Calculator](https://www.calculator.land/calculators/3-phase-motor/)

Works out the power of a three-phase motor in three ways: mechanical output from the input power in kW and the efficiency, electrical input from line voltage, line current and power factor (√3 × V × I × cos φ), or mechanical output from those three values and the efficiency. The result is shown in kW and horsepower (HP) and updates as you type, and clicking a part of the formula explains what it stands for.

### [Electricity Cost Calculator](https://www.calculator.land/calculators/electrical-appliance-cost/)

Estimates how much electricity a household appliance uses and what it costs per day, month and year, from its wattage, the time it runs each day and the price per kWh. You can pick an appliance from a list with typical wattages or enter your own values, and the advanced settings adjust the days per month, the months per year and the duty cycle for appliances that switch themselves on and off. It also estimates the CO₂ emissions per year.

### [Ohm's Law & Power Calculator](https://www.calculator.land/calculators/ohms-law/)

Works out the two missing values of voltage, current, resistance and power when you enter any two of them, each in a unit you choose (for example mV, kΩ or kW). It checks the power against the resistor wattage rating you select, warns when the resistance is zero, and the results can be copied.

### [Watt's Law Calculator](https://www.calculator.land/calculators/watts-law/)

Solves Watt's law (P = V × I) for power, voltage or current: you choose what to find, enter the other two values and press the calculate button. The result is shown with the formula and the numbers used, and a line chart shows the power for currents from 0 to 20 A at that voltage.