Enter any two electrical values — voltage, current, resistance, or power — and instantly calculate the remaining values.
Fill in exactly 2 fields. Leave the others blank to calculate them.
Ohm's Law defines the relationship between voltage (V), current (I), resistance (R), and power (P) in electrical circuits. If you know any two values, you can calculate the other two.
| Find | Formula 1 | Formula 2 | Formula 3 |
|---|---|---|---|
| Voltage (V) | V = I × R | V = P ÷ I | V = √(P × R) |
| Current (I) | I = V ÷ R | I = P ÷ V | I = √(P ÷ R) |
| Resistance (R) | R = V ÷ I | R = V² ÷ P | R = P ÷ I² |
| Power (P) | P = V × I | P = I² × R | P = V² ÷ R |
| Application | Voltage | Typical Amps | Watts |
|---|---|---|---|
| LED bulb | 120V | 0.08A | 10W |
| Phone charger | 5V | 2A | 10W |
| USB-C fast charge | 20V | 3A | 60W |
| Standard outlet (US) | 120V | 15A max | 1,800W |
| Kitchen/bath circuit | 120V | 20A max | 2,400W |
| Dryer / range outlet | 240V | 30A | 7,200W |
| EV charger (Level 2) | 240V | 40A | 9,600W |
| Microwave | 120V | 8-12A | 1,000-1,500W |
| Space heater | 120V | 12.5A | 1,500W |
| Car battery | 12V | varies | varies |
The National Electrical Code requires that continuous loads (running 3+ hours) must not exceed 80% of the breaker's rated capacity. This means:
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