Ohm's Law Calculator
Calculate voltage, current, resistance, and power using Ohm's Law equations. Enter any 2 values and the calculator will automatically compute the remaining values in real-time.
Input Values
Voltage
Current
Resistance
Power
Applied Formulas
Ohm's Law
V = I × R
I = V / R
R = V / I
Power Formulas
P = V × I
P = V² / R
P = I² × R
Values Distribution
Circuit Diagram
┌─────────────┐
│ │
│ Voltage │
┌───┤ Source ├───┐
│ │ │ │
│ └─────────────┘ │
│ │
│ +V │
│ │
─┴─ ┌───┐ │
─┬─ ←I │ R │ │
│ └───┘ │
│ │
│ GND │
│ │
└─────────────────────┘
V = Voltage (110 V)
I = Current (0.2 A)
R = Resistance (? Ω)
P = Power (? W)
Ohm's Law is the fundamental relationship governing electrical circuits. It states that voltage equals current times resistance. This calculator solves for any of the four electrical quantities: voltage (V), current (I), resistance (R), and power (P), given any two known values.
Ohm's Law Formulas
The Ohm's Law wheel shows all relationships between V, I, R, and P. Given any two quantities, you can find the other two.
V = I × R (Voltage = Current × Resistance) I = V / R (Current = Voltage / Resistance) R = V / I (Resistance = Voltage / Current) Power formulas: P = V × I P = I² × R P = V² / R
SI units: V = Volts, I = Amperes (A), R = Ohms (Ω), P = Watts (W).
Practical Electrical Examples
| Scenario | Given | Find |
|---|---|---|
| LED resistor sizing | V supply, V LED, I LED | R = (V supply - V LED) / I |
| Circuit breaker check | V, R (load) | I = V/R → compare to breaker rating |
| Heater power | 120V, 10Ω | P = V²/R = 1,440 W |
| Battery life estimate | V battery, R load | I = V/R → runtime = Ah/I |
Frequently Asked Questions
Is Ohm's Law always accurate?⌄
Ohm's Law applies exactly to ohmic materials (pure resistors) where resistance is constant regardless of current or voltage. Many real components are non-ohmic: diodes have non-linear V-I curves, transistors have complex relationships, and some materials change resistance with temperature. Ohm's Law is a fundamental approximation that works well for resistive circuits at normal conditions.
What is the difference between AC and DC resistance?⌄
DC resistance is straightforward (R = V/I). AC circuits have impedance (Z), which includes resistance (R) and reactance (X) from inductors and capacitors: Z = √(R² + X²). Ohm's Law extends to AC as V = I × Z. At DC (frequency 0), capacitors block current (infinite impedance) and inductors have zero impedance.
Why does higher resistance lead to lower current?⌄
Resistance opposes the flow of electrons. Higher resistance means electrons face more opposition as they move through the material. For the same applied voltage, more resistance results in fewer electrons flowing per second (lower current). This is analogous to water flow: a narrower pipe (more resistance) reduces flow rate for the same water pressure.
What is power dissipation and why does it matter?⌄
Power dissipation (P = I² × R) is the energy converted to heat in a resistor. This matters for component selection: a resistor must be rated to handle the power it will dissipate without overheating. For example, a 100Ω resistor carrying 100mA dissipates 1W and requires at least a 1W-rated component, or preferably a 2W component for a safety margin.