Ohm's Law Calculator
Calculate voltage (V), current (I), resistance (R), and power (P) instantly. Enter any two values to find the others.
Ohm's Law Calculator
Enter any two values to calculate the rest
How to Use
- • Enter any two known values (V, I, R, or P)
- • The calculator automatically computes the remaining values
- • All calculations use standard SI units (Volts, Amperes, Ohms, Watts)
- • Results show engineering notation (mA, kΩ, etc.) for convenience
Ohm's Law Formulas
Voltage
V = I × R
Voltage equals Current times Resistance. Measured in Volts (V).
Current
I = V / R
Current equals Voltage divided by Resistance. Measured in Amperes (A).
Resistance
R = V / I
Resistance equals Voltage divided by Current. Measured in Ohms (Ω).
Power
P = V × I
P = I² × R = V² / R
Power can be calculated multiple ways. Measured in Watts (W).
Understanding Ohm's Law
Master the foundational principle of electrical engineering that governs the relationship between voltage, current, and resistance.
What is Ohm's Law?
Discovered by German physicist Georg Simon Ohm in 1827, Ohm's Law states that the current through a conductor is directly proportional to the voltage across it and inversely proportional to its resistance.
Key Electrical Quantities
Voltage
Electrical Potential Difference
Measured in Volts (V). Think of it as the "pressure" pushing electrons through a conductor. Common sources: batteries (1.5V, 9V, 12V) and outlets (120V, 240V).
Current
Flow of Electric Charge
Measured in Amperes (A). Represents the rate of electron flow through a conductor—like water flowing through a pipe. Higher current = more electrons per second.
Resistance
Opposition to Current Flow
Measured in Ohms (Ω). All materials resist electron flow; copper has low resistance (conductor), rubber has high resistance (insulator). Resistors provide precise resistance values.
Power
Rate of Energy Transfer
Measured in Watts (W). The rate at which electrical energy is converted (often to heat). Calculate using P = V×I, P = I²R, or P = V²/R.
Practical Applications
LED Circuits
Calculate resistor for current limiting
Power Supplies
Size supply for load requirements
Wire Sizing
Calculate voltage drop in cables
Troubleshooting
Diagnose circuit problems
Component Selection
Choose proper power ratings
Circuit Analysis
Understand circuit behavior
Example Calculations
A 12V battery is connected to a 100Ω resistor. What is the current flowing through the circuit?
I = V / R = 12V / 100Ω = 0.12A (120mA)
An LED needs 20mA at 2V forward voltage. With a 5V supply, what resistor value is needed?
R = (Vsupply - VLED) / I = (5V - 2V) / 0.02A = 150Ω
A 470Ω resistor carries 50mA of current. What is the power dissipation?
P = I² × R = (0.05A)² × 470Ω = 1.175W
Tip: Use a 2W resistor for safety margin!
Frequently Asked Questions
What is Ohm's Law?
Ohm's Law is a fundamental principle in electrical engineering that describes the relationship between voltage (V), current (I), and resistance (R). The law states that the current flowing through a conductor is directly proportional to the voltage across it and inversely proportional to its resistance. The formula is V = I × R, where V is voltage in volts, I is current in amperes, and R is resistance in ohms.
How do I calculate voltage using Ohm's Law?
To calculate voltage using Ohm's Law, multiply the current (in amperes) by the resistance (in ohms). The formula is: V = I × R. For example, if a circuit has 2 amperes of current flowing through a 10-ohm resistor, the voltage is V = 2A × 10Ω = 20 volts.
How do I calculate current using Ohm's Law?
To calculate current using Ohm's Law, divide the voltage (in volts) by the resistance (in ohms). The formula is: I = V / R. For example, if you have 12 volts across a 4-ohm resistor, the current is I = 12V / 4Ω = 3 amperes.
How do I calculate resistance using Ohm's Law?
To calculate resistance using Ohm's Law, divide the voltage (in volts) by the current (in amperes). The formula is: R = V / I. For example, if you have 24 volts and 2 amperes of current, the resistance is R = 24V / 2A = 12 ohms.
How do I calculate power using Ohm's Law?
Power can be calculated using several formulas derived from Ohm's Law: P = V × I (voltage times current), P = I²R (current squared times resistance), or P = V²/R (voltage squared divided by resistance). All three formulas give the same result and power is measured in watts (W).
What units are used in Ohm's Law?
In Ohm's Law calculations: Voltage (V) is measured in volts (V), Current (I) is measured in amperes or amps (A), Resistance (R) is measured in ohms (Ω), and Power (P) is measured in watts (W). For proper calculations, always ensure your values are in these base units or convert them accordingly.
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