Ohm's law and power
Ohm's law ties voltage, current and resistance together; the power law adds watts. Any two values determine the other two.
Enter any two values. The other two are calculated.
V
A
Ω
W
- Voltage
- 13.8 V
- Current
- 3.623 A
- Resistance
- 3.809 Ω
- Power
- 50 W
E = I × RP = E × IP = I² × RP = E² / R
How it works
- E is voltage in volts, I is current in amperes, R is resistance in ohms and P is power in watts. R = E / I and P = I x E; the other forms follow by substitution.
- Example: a 13.8 V radio drawing 20 A on transmit uses 276 W from its power supply.
Learn more: Electronics basics
Sources: Radio Mathematics (ARRL Handbook supplement) (ARRL); 2026-2030 Technician question pool (NCVEC Question Pool Committee)
Practice the exam questions: T5 Electrical Principles (Technician), G5 Electrical Principles (General)