Ohm's Law Calculator

Calculate any value (voltage, current, or resistance) when you know the other two. Power is automatically calculated.

Ohm's Law: V = I * R Where: • V = Voltage (volts) • I = Current (amperes) • R = Resistance (ohms) Rearrangements: • I = V / R • R = V / I Power formulas: • P = V * I • P = I² * R • P = V² / R
Example 1 (Find Voltage): Current = 2 A, Resistance = 10 Ω V = 2 * 10 = 20 V P = 20 * 2 = 40 W Example 2 (Find Current): Voltage = 12 V, Resistance = 6 Ω I = 12 / 6 = 2 A P = 12 * 2 = 24 W Example 3 (Find Resistance - LED circuit): Voltage = 9 V, Current = 0.02 A (20 mA) R = 9 / 0.02 = 450 Ω P = 9 * 0.02 = 0.18 W Example 4 (Household circuit): Voltage = 120 V, Resistance = 12 Ω (heater) I = 120 / 12 = 10 A P = 120 * 10 = 1200 W (1.2 kW)

What is Ohm's Law?

Ohm's Law states that voltage (V) equals current (I) times resistance (R): V = IR. It describes the relationship between voltage, current, and resistance in electrical circuits.

How do I calculate power using Ohm's Law?

Power (P) can be calculated using P = VI (power equals voltage times current). Alternatively, use P = I²R or P = V²/R depending on which values you know.

What happens in series circuits?

In series circuits, current is the same through all components, but voltage divides across them. Total resistance equals the sum of individual resistances: R_total = R₁ + R₂ + R₃...

What happens in parallel circuits?

In parallel circuits, voltage is the same across all components, but current divides. For parallel resistances: 1/R_total = 1/R₁ + 1/R₂ + 1/R₃...

What are common applications of Ohm's Law?

Ohm's Law is used in circuit design, troubleshooting electrical systems, calculating LED resistors, sizing power supplies, and designing electronic devices. It's fundamental to all electrical engineering.

Does Ohm's Law work for AC circuits?

Ohm's Law applies to AC circuits, but resistance is replaced by impedance (Z), which includes resistance and reactance from capacitors and inductors. The formula becomes V = IZ.

Why is my calculated power different from rated power?

Actual power consumption may differ from calculations due to component tolerances, temperature effects, non-linear behavior, or reactive components. Calculated values assume ideal resistive loads.

What units should I use?

Use volts (V) for voltage, amperes (A) for current, and ohms (Ω) for resistance. Power will be calculated in watts (W). Ensure consistent units for accurate results.

Can I use Ohm's Law for all materials?

Ohm's Law applies to ohmic materials (conductors that obey a linear V-I relationship). Some materials like diodes, transistors, and thermistors are non-ohmic and don't follow this linear relationship.

How do I size a current-limiting resistor?

For LEDs, use R = (V_source - V_LED) / I_LED. For example, a 5V source with a 2V LED at 20mA needs R = (5-2)/0.02 = 150Ω. Choose the next standard value (e.g., 180Ω).

What is the difference between voltage drop and voltage source?

Voltage source provides electrical potential (battery, power supply). Voltage drop is the reduction in voltage across a component due to resistance. Total voltage drops equal the source voltage in a circuit.

How does temperature affect resistance?

Most conductors increase resistance with temperature (positive temperature coefficient). For precision work, consider temperature effects, but this calculator assumes constant resistance at room temperature.