Electricity Calculator

Q: What happens if resistance is zero?

Zero resistance means a short circuit—current would theoretically be infinite for any voltage. In practice, wires and components always have some resistance. This calculator requires positive non-zero values for meaningful results. Zero resistance (or values approaching zero) indicates a potential safety hazard in real circuits.

Calculate voltage, current, resistance, and power using Ohm's Law and Watt's Law. Enter any two known values and instantly solve for the other two with detailed step-by-step formulas.

Free to useNo sign-up requiredUpdated Feb 2026

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⚡ Quick Examples — click to fill:

💡 120V, 60Ω Bulb 🔋 5A, 100W Motor ⚡ 240V, 10A Heater ⏛ 8Ω, 200W Speaker 🔌 12V, 3A DC Supply 📱 5V USB, 10W

Enter exactly 2 known values. Leave the other 2 fields blank. The calculator will solve for both unknowns.

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Voltage (V)

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Current (A)

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Resistance (Ω)

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Power (W)

Decimal Precision

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About Electricity Calculator

Welcome to the Electricity Calculator, a comprehensive tool that uses Ohm's Law and Watt's Law to solve for any two unknown electrical quantities. Enter any two of the four values — voltage (V), current (I), resistance (R), or power (P) — and instantly calculate the remaining two with detailed step-by-step formula breakdowns.

The Fundamental Laws of Electricity

⚡ Ohm's Law

V = I × R

Voltage equals current multiplied by resistance. Discovered by Georg Simon Ohm in 1827, this law describes the linear relationship between voltage, current, and resistance in a conductor.

⚙ Watt's Law

P = V × I

Power equals voltage multiplied by current. Named after James Watt, this law defines electrical power consumption — the rate at which electrical energy is transferred in a circuit.

All 12 Formulas of the Power Wheel

By combining Ohm's Law and Watt's Law, we derive 12 essential formulas — three for each electrical quantity. This calculator uses the appropriate formula based on your two known inputs:

Voltage Formulas

$$V = I \times R \quad\quad V = \frac{P}{I} \quad\quad V = \sqrt{P \times R}$$

Current Formulas

$$I = \frac{V}{R} \quad\quad I = \frac{P}{V} \quad\quad I = \sqrt{\frac{P}{R}}$$

Resistance Formulas

$$R = \frac{V}{I} \quad\quad R = \frac{V^2}{P} \quad\quad R = \frac{P}{I^2}$$

Power Formulas

$$P = V \times I \quad\quad P = \frac{V^2}{R} \quad\quad P = I^2 \times R$$

Understanding Electrical Quantities

Quantity	Symbol	Unit	Description
Voltage	V	Volts (V)	Electrical potential difference — the "pressure" that pushes electrons through a circuit
Current	I	Amperes (A)	Rate of electron flow — the amount of charge moving through a conductor per second
Resistance	R	Ohms (Ω)	Opposition to current flow — how much a material resists the passage of electrons
Power	P	Watts (W)	Rate of energy transfer — how quickly electrical energy is consumed or produced

How to Use This Calculator

Identify two known values: Determine which two electrical quantities you know from your circuit or problem.
Enter the values: Input the two known values in their respective fields. Leave the other two fields blank.
Click Calculate: The calculator uses the appropriate formula from the Ohm's Law power wheel to solve for the two unknown values.
Review the solution: See all four values, step-by-step formulas, and a verification check.

Practical Examples

Household Light Bulb

A standard 60W light bulb on a 120V circuit: Using P = V × I, we get I = P/V = 60/120 = 0.5A. Using Ohm's Law, R = V/I = 120/0.5 = 240Ω.

Electric Heater

A 1500W space heater on 120V: Current I = 1500/120 = 12.5A, and Resistance R = 120/12.5 = 9.6Ω. This explains why heaters need dedicated circuits — 12.5A is significant.

LED vs Incandescent

A 10W LED produces similar light to a 60W incandescent bulb. On 120V: LED draws only 0.083A vs 0.5A for incandescent — 6× less current for the same brightness.

The Water Analogy

Electricity is often compared to water flowing through pipes:

Voltage = Water Pressure: Higher voltage means more "push" driving electrons through the circuit
Current = Flow Rate: More current means more electrons passing through per second
Resistance = Pipe Width: Narrower pipes (higher resistance) restrict flow for the same pressure
Power = Work Done: More power means more energy delivered, like a high-pressure wide pipe turning a water wheel faster

Frequently Asked Questions

What is Ohm's Law?

Ohm's Law states that voltage (V) equals current (I) multiplied by resistance (R), expressed as V = I × R. It describes the linear relationship between voltage, current, and resistance in an electrical circuit. This fundamental law allows you to calculate any one of the three quantities if the other two are known.

What is Watt's Law?

Watt's Law states that electrical power (P) equals voltage (V) multiplied by current (I), expressed as P = V × I. Combined with Ohm's Law, this gives us 12 useful formulas to calculate any electrical quantity (voltage, current, resistance, or power) from any two known values.

How many formulas does the Ohm's Law wheel have?

The Ohm's Law power wheel contains 12 formulas: 3 for voltage (V=IR, V=P/I, V=√(PR)), 3 for current (I=V/R, I=P/V, I=√(P/R)), 3 for resistance (R=V/I, R=V²/P, R=P/I²), and 3 for power (P=VI, P=V²/R, P=I²R). You only need to know any two values to solve for the remaining two.

Can I calculate power from resistance and current alone?

Yes. Using the formula P = I² × R, you can calculate power directly from current and resistance. For example, if current is 3A and resistance is 10Ω, power = 3² × 10 = 90 watts. You can also then find voltage using V = I × R = 30V.

What units are used in electrical calculations?

The four fundamental electrical units are: Voltage in Volts (V), Current in Amperes (A), Resistance in Ohms (Ω), and Power in Watts (W). These are SI units. For larger values, prefixes like kilo (kΩ, kW) or mega (MΩ, MW) are used. For smaller values, milli (mA, mV) or micro (μA) are common.

What happens if resistance is zero?

Zero resistance means a short circuit — current would theoretically be infinite for any voltage. In practice, wires and components always have some resistance. This calculator requires positive non-zero values for meaningful results. Zero resistance (or values approaching zero) indicates a potential safety hazard in real circuits.

Additional Resources

Reference this content, page, or tool as:

"Electricity Calculator" at https://MiniWebtool.com/electricity-calculator/ from MiniWebtool, https://MiniWebtool.com/

by miniwebtool team. Updated: Feb 11, 2026

Developer API available: Run this tool from your app, automation, or agent with one JSON HTTP request. View API docs