How do volts, amps, and watts relate to each other?

Watts = Volts × Amps. If you know any two values, you can calculate the third. For example, a device drawing 5 amps from a 120V outlet uses 600 watts of power.

Ohm's law states that Voltage = Current × Resistance, or V = I × R. Combined with the power equation (P = V × I), you can derive 12 useful formulas relating voltage, current, resistance, and power.

What is the difference between AC and DC?

DC (direct current) flows in one direction (batteries, solar panels, USB). AC (alternating current) reverses direction periodically — 60 times per second (60 Hz) in the US, 50 Hz in most other countries. Wall outlets provide AC; most electronics convert it to DC internally.

Electrical Units: Volts, Amps, Watts, and Ohms Explained

The Four Basic Electrical Units

Unit	Symbol	Measures	Water Analogy
Volt (V)	V	Electrical pressure	Water pressure
Ampere (A)	A or I	Current flow	Water flow rate
Watt (W)	W or P	Power	Total water energy
Ohm (Ω)	Ω or R	Resistance	Pipe narrowness

Key Formulas

Ohm's Law: V = I × R
Power: P = V × I
Power (from R): P = I² × R = V² / R
Current: I = P / V = V / R

Common Household Examples

Device	Voltage	Watts	Amps
Phone charger	5V (USB)	5-20W	1-4A
LED bulb	120V	10W	0.08A
Microwave	120V	1,000W	8.3A
Hair dryer	120V	1,500W	12.5A
Electric oven	240V	5,000W	20.8A
EV charger (L2)	240V	7,200W	30A

Circuit Breaker Sizing

Max watts on a circuit = Voltage × Breaker amps × 0.8

The 80% rule means a 15-amp, 120V circuit safely handles 1,440W continuous (15 × 120 × 0.8). A 20-amp circuit handles 1,920W.

Global Voltage Standards

Region	Voltage	Frequency
US, Canada, Mexico	120V	60 Hz
Europe, UK, Asia	220-240V	50 Hz
Japan	100V	50/60 Hz

Convert power units with our power converter.