Watts Volts Amps Ohms Calculator
Enter any 2 values to calculate the remaining electrical quantities
Enter any 2 values to get the other values and press the Calculate button
Ohm's Law Explained
Ohm's Law states that the current through a conductor between two points is directly proportional to the voltage across the two points, and inversely proportional to the resistance between them. The formula is V = I × R, where V is voltage in volts, I is current in amps, and R is resistance in ohms. This law was named after German physicist Georg Simon Ohm, who first described it in 1827.
Watt's Law Explained
Watt's Law defines the relationship between power, voltage, and current in an electrical circuit. The basic formula is P = V × I, where P is power in watts, V is voltage in volts, and I is current in amps. By combining Watt's Law with Ohm's Law, we derive additional formulas: P = I² × R (power from current and resistance) and P = V² ÷ R (power from voltage and resistance). These formulas form the foundation of all electrical calculations.
Ohm's Law Wheel
Click each quadrant to see its formulas.
V = I × R | P = V × I Key Electrical Formulas
The complete set of formulas connecting watts, volts, amps, and ohms
Voltage
V = I × R V = P ÷ I V = √(P × R) Current
I = V ÷ R I = P ÷ V I = √(P ÷ R) Resistance
R = V ÷ I R = V² ÷ P R = P ÷ I² Power
P = V × I P = I² × R P = V² ÷ R Example Calculations
Step-by-step electrical calculation examples
Find Voltage and Power from Current and Resistance
Given: Current (I) = 5 A, Resistance (R) = 24 Ω
V = I × R = 5 × 24 = 120 V P = V × I = 120 × 5 = 600 W Find Current and Resistance from Voltage and Power
Given: Voltage (V) = 240 V, Power (P) = 1200 W
I = P ÷ V = 1200 ÷ 240 = 5 A R = V ÷ I = 240 ÷ 5 = 48 Ω Find Voltage and Current from Power and Resistance
Given: Power (P) = 100 W, Resistance (R) = 400 Ω
V = √(P × R) = √(100 × 400) = √40000 = 200 V I = V ÷ R = 200 ÷ 400 = 0.5 A Watts Volts Amps Ohms Quick Reference
Common electrical values at standard voltages
| Voltage (V) | Current (A) | Power (W) | Resistance (Ω) |
|---|---|---|---|
| 5 V | 0.5 A | 2.5 W | 10 Ω |
| 5 V | 2 A | 10 W | 2.5 Ω |
| 5 V | 10 A | 50 W | 0.5 Ω |
| 5 V | 20 A | 100 W | 0.25 Ω |
| 12 V | 1 A | 12 W | 12 Ω |
| 12 V | 5 A | 60 W | 2.4 Ω |
| 12 V | 15 A | 180 W | 0.8 Ω |
| 24 V | 0.5 A | 12 W | 48 Ω |
| 24 V | 2 A | 48 W | 12 Ω |
| 24 V | 10 A | 240 W | 2.4 Ω |
| 24 V | 20 A | 480 W | 1.2 Ω |
| 48 V | 1 A | 48 W | 48 Ω |
| 48 V | 5 A | 240 W | 9.6 Ω |
| 48 V | 15 A | 720 W | 3.2 Ω |
| 120 V | 0.5 A | 60 W | 240 Ω |
| 120 V | 2 A | 240 W | 60 Ω |
| 120 V | 10 A | 1200 W | 12 Ω |
| 120 V | 20 A | 2400 W | 6 Ω |
| 240 V | 1 A | 240 W | 240 Ω |
| 240 V | 5 A | 1200 W | 48 Ω |
Our Electrical Calculators
Free online tools for engineers, students, and professionals
Watts to Volts Calculator
Convert power (W) to voltage (V) for DC, AC single-phase, and AC three-phase circuits.
Watts Volts Amps Ohms Calculator
Calculate any 2 unknown electrical values from Resistance, Current, Voltage, and Power.
Watts to Electron Volts Converter
Convert energy between watt-seconds, watt-hours, and electron volts (eV).
Frequently Asked Questions
How do I use the Watts Volts Amps Ohms Calculator?
Enter any 2 of the 4 values — Resistance (Ω), Current (A), Voltage (V), or Power (W) — and click Calculate. The calculator uses Ohm's Law (V = I × R) and Watt's Law (P = V × I) to compute the remaining 2 values automatically.
What is the relationship between Watts, Volts, Amps, and Ohms?
These four units are interconnected through Ohm's Law and Watt's Law. Volts (V) measure electrical pressure, Amps (A) measure current flow, Ohms (Ω) measure resistance, and Watts (W) measure power. V = I × R (Ohm's Law) and P = V × I (Watt's Law) are the two fundamental equations connecting them.
What is Ohm's Law?
Ohm's Law states that voltage equals current multiplied by resistance: V = I × R. It can also be rearranged to find current (I = V ÷ R) or resistance (R = V ÷ I). This law applies to any DC circuit and to AC circuits with purely resistive loads.
What is Watt's Law?
Watt's Law states that power equals voltage multiplied by current: P = V × I. By combining with Ohm's Law, you get P = I² × R and P = V² ÷ R. This law is used to calculate electrical power consumption in circuits.
Can I calculate Watts from Amps and Ohms?
Yes. Using the formula P = I² × R, multiply the square of the current in amps by the resistance in ohms. For example, 3 A through 10 Ω: P = 3² × 10 = 9 × 10 = 90 W.
How do I find Amps from Watts and Volts?
Divide power by voltage: I = P ÷ V. For example, a 600 W device running at 120 V draws 600 ÷ 120 = 5 A of current.
What is the difference between kΩ and Ω?
kΩ (kilohm) equals 1,000 Ω (ohms). Similarly, MΩ (megohm) equals 1,000,000 Ω. These prefixes are used for large resistance values. The calculator supports automatic unit conversion between these scales.
Why do I need to enter exactly 2 values?
With 4 variables (V, I, R, P) connected by 2 independent equations (Ohm's Law and Watt's Law), you need exactly 2 known values to solve for the remaining 2 unknowns. Entering fewer values leaves the problem underdetermined, while entering more could create contradictions.