Ohm’s Law Calculator

Ohm’s Law Calculator

Calculate Voltage (V), Current (I), Resistance (R), or Power (P) instantly.

Type in any two fields. The others will auto-calculate in blue.
i Voltage is the electric pressure or potential difference between two points.
i Current is the rate of flow of electric charge past a point or region.
i Resistance is a measure of the opposition to current flow in an electrical circuit.
i Electric power is the rate at which electrical energy is transferred by an electric circuit.
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Ohms Law Calculator by VersaCalculator

How to Use This Ohm’s Law Calculator

Enter Any Two Values: You can input Voltage (V), Current (I), Resistance (R), or Power (P).

What is Ohm’s Law?

At its core, Ohm’s Law explains the relationship between three fundamental elements of electricity: Voltage, Current, and Resistance.

Discovered by Georg Ohm in 1827, this law states that the electric current flowing through a conductor is directly proportional to the voltage applied across it and inversely proportional to the resistance.

In simpler terms: if you increase the pressure (Voltage), the flow (Current) increases. If you increase the obstacle (Resistance), the flow decreases.

The Water Pipe Analogy

To visualize this without the math, imagine electricity as water flowing through a pipe:

  • Voltage (V) is the water pressure. More pressure pushes water faster.
  • Current (I) is the rate of water flow (how much water passes a point per second).
  • Resistance (R) is the size of the pipe. A narrow pipe (high resistance) restricts flow; a wide pipe (low resistance) allows water to rush through easily.

Understanding the Variables

Voltage (V or E)

  • Unit: Volts (V)
  • Definition: The potential difference or “electrical push” between two points. In our calculator, you can input values in millivolts ($mV$), Volts ($V$), or Kilovolts (kV).

Current (I)

  • Unit: Amperes or Amps (A)
  • Definition: The rate at which electric charge flows. A higher current means more electrons are moving through the circuit.

Resistance (R)

  • Unit: Ohms (Ω)
  • Definition: A material’s tendency to resist the flow of charge. Insulators like rubber have massive resistance; conductors like copper have very little.

Electric Power (P)

  • Unit: Watts (W)
  • Definition: While not part of Ohm’s original law, Power is essential in circuit design. It represents the rate at which energy is consumed or generated. This calculator com

The Formulas

1. To Find Voltage (V)

If you know the Current and Resistance:

V = I x R

2. To Find Current (I)

If you know the Voltage and Resistance:

I = V / R

3. To Find Resistance (R)

If you know the Voltage and Current:

R = V / I

4. To Find Power (P)

Combining Ohm’s Law with power calculations gives us three ways to find Watts:

  • If you know V and I: P = V x I
  • If you know I and R: P = I^2 x R
  • If you know V and R: P = V^2 / R

Note: My calculator handles all these permutations automatically. You don’t need to memorize the formulas, but you can always view them in the “Calculation Steps” section after computing.

Practical Applications

1. Sizing Fuses and Breakers

If you are installing a 1200W heater on a 120V circuit, you need to know the current to choose the right fuse.

  • Current = Power / Voltage
  • 1200W / 120V = 10 Amps.You would need a fuse slightly larger than 10A to prevent nuisance tripping.

2. Protecting LEDs

LEDs will burn out if connected directly to a battery. You must calculate the correct resistor value to limit the current to a safe level (usually 20mA for standard LEDs).

3. Troubleshooting Circuits

If a device isn’t working, measuring the resistance and voltage can tell you if a component is shorted (zero resistance) or open (infinite resistance).

A Note on AC vs. DC

Ohm’s Law is universally applicable to DC (Direct Current) circuits.

For AC (Alternating Current) circuits, the law still holds true for purely resistive loads (like heaters and incandescent bulbs). However, if your circuit includes capacitors or inductors, “Resistance” becomes “Impedance” (Z). While this calculator is accurate for general wiring and resistive AC loads, complex AC circuits require vector calculations.

FAQs

Q1. Why does the resistance change when the component gets hot?

A: In the real world, resistance isn’t always constant. As a light bulb filament heats up, its resistance increases. This is why a bulb often blows right when you turn it on the resistance is lowest when cold, causing a momentary spike in current.

Q2. What is the difference between Conventional Current and Electron Flow?

A: In engineering, we typically calculate “Conventional Current,” which flows from Positive to Negative. Physically, electrons actually flow from Negative to Positive. The math works identically regardless of which convention you visualize.

Q3. Can I calculate Power Factor with this?

A: No. This tool assumes a Power Factor of 1.0 (purely resistive load). For inductive loads (like motors), you would need to account for the phase angle difference between voltage and current.

Sources: Calculator.net, Ohms Law Calculator, DigiKey, RapidTables, Omni Calculator, Rhopoint Components, Keysight, RS Components, Watlow.