Ohm's Law Calculator
Calculate voltage, current, resistance, and power using Ohm's Law. Free electronics calculator with instant results.
Ohm's Law Calculator
Calculate voltage, current, resistance, or power from any two known values.
I want to calculate:
Enter any two of the three values below:
A
Ω
W
Ohm's Law Triangle
P = V × I
P = I² × R
P = V² / R
V = √(P × R)
Result
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Enter two values to calculate
Common Values
LED2V / 20mA
USB Port5V / 500mA
Car Battery12V / -
Household (US)120V / -
Household (EU)230V / -
Understanding Ohm's Law
Ohm's Law is the fundamental relationship in electrical circuits, stating that the voltage (V) across a conductor is directly proportional to the current (I) flowing through it, with the constant of proportionality being the resistance (R): V = I × R.
The Four Quantities
- Voltage (V): Measured in Volts (V). The electrical pressure or potential difference that drives current through a circuit.
- Current (I): Measured in Amperes (A). The flow rate of electric charge through a conductor.
- Resistance (R): Measured in Ohms (Ω). The opposition to current flow in a circuit.
- Power (P): Measured in Watts (W). The rate at which electrical energy is consumed or produced.
Key Formulas
- V = I × R (Voltage = Current × Resistance)
- I = V / R (Current = Voltage / Resistance)
- R = V / I (Resistance = Voltage / Current)
- P = V × I (Power = Voltage × Current)
- P = I² × R (Power = Current² × Resistance)
- P = V² / R (Power = Voltage² / Resistance)
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How to Use
- 1Enter any two known electrical values: voltage (V), current (I), resistance (R), or power (P).
- 2Select the values you want to calculate from the remaining unknowns.
- 3View the calculated results instantly with the formulas used.
Frequently Asked Questions
What is Ohm's Law?
Ohm's Law states that the current flowing through a conductor is directly proportional to the voltage and inversely proportional to the resistance. The formula is V = I x R, where V is voltage in volts, I is current in amps, and R is resistance in ohms.
How do I calculate voltage?
Voltage (V) equals current (I) multiplied by resistance (R): V = I x R. For example, if 2 amps flow through a 5 ohm resistor, the voltage is 10 volts.
How do I calculate current?
Current (I) equals voltage (V) divided by resistance (R): I = V / R. For example, 12 volts across a 4 ohm resistor produces 3 amps of current.
How is electrical power related to voltage and current?
Power (P) in watts equals voltage (V) multiplied by current (I): P = V x I. It can also be expressed as P = I^2 x R or P = V^2 / R.
What units are used in electrical calculations?
Voltage is measured in volts (V), current in amperes or amps (A), resistance in ohms (ohm), and power in watts (W). These are all SI units.