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
What is Watts Volts Amps Ohms Calculator?
The Watts Volts Amps Ohms Calculator is a free online electrical calculator that solves for any two unknown values when you provide two known electrical quantities. Enter any combination of resistance (Ω), current (A), voltage (V), or power (W), and the calculator instantly computes the remaining values using Ohm's Law and Watt's Law. This tool exists because engineers, electricians, students, and hobbyists constantly need to convert between these four fundamental electrical units — and doing it by hand with multiple formulas is slow and error-prone.
Why Use This Calculator?
Manually calculating electrical values requires remembering and applying multiple formulas from both Ohm's Law and Watt's Law. The Watts Volts Amps Ohms Calculator eliminates that complexity — just enter any 2 values and get instant, accurate results for the other 2. Whether you're sizing a circuit breaker, checking a motor's current draw, verifying a resistor's power rating, or solving a homework problem, this calculator gives you the answer in seconds with zero chance of formula errors.
Ohm's Law Wheel
Click each quadrant to see its formulas.
V = I × R | P = V × I Watts Volts Amps Ohms Calculator Formula
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.