Electrical Engineering
Enter any two of voltage, current, or resistance to find all four electrical quantities.
Electrical Circuit Parameters
Voltage: 12 V
Current: 0.12 A
Resistance: 100 Ω
Power: 1.44 W
Ohm's Law states V = IR (voltage equals current times resistance). Power is calculated as P = VI.
Ohm's Law Calculator is an electrical engineering tool that applies the relationship V = IR to find missing electrical values. Given any two of voltage (V, measured in volts), current (I, measured in amps), or resistance (R, measured in ohms), the calculator computes the other two values and calculates power (P = VI, measured in watts). It works for DC circuits and simple AC analysis.
The calculator uses three core equations: (1) V = IR (voltage equals current times resistance), (2) R = V/I (resistance equals voltage divided by current), and (3) P = VI (power equals voltage times current). Depending on which two values you supply, the tool solves the system of equations algebraically and displays all four quantities instantly. Results are formatted with SI prefixes (milli-, kilo-, mega-) for readability.
V = IR | I = V/R | R = V/I | P = VIOhm's Law (V = IR): voltage across a conductor is directly proportional to current flowing through it, with resistance as the constant of proportionality. Power (P = VI): the rate of energy transfer in a circuit is the product of voltage and current. These equations are mathematically equivalent and can be rearranged to solve for any unknown.
| Input | Result | Notes |
|---|---|---|
| Voltage: 12V, Resistance: 100Ω, Current: blank | Current: 0.12A, Power: 1.44W | A 12-volt battery powering a 100-ohm resistor draws 0.12 amps and dissipates 1.44 watts as heat. |
| Voltage: 5V, Current: 0.5A, Resistance: blank | Resistance: 10Ω, Power: 2.5W | A circuit drawing 0.5 amps from a 5-volt supply has 10 ohms of resistance and consumes 2.5 watts. |
| Current: 2A, Resistance: 6Ω, Voltage: blank | Voltage: 12V, Power: 24W | A 2-amp current through a 6-ohm resistance requires 12 volts and dissipates 24 watts. |
Voltage (V) is the electrical potential difference, like water pressure in a pipe. Current (I) is the flow of charge, like the rate of water flowing. Resistance (R) is the opposition to flow. Ohm's Law ties them together: higher voltage or lower resistance increases current.
Power (P = VI, in watts) tells you how much energy is consumed per second. This is critical for: selecting resistor wattage ratings (to avoid burnout), calculating heat dissipation, estimating electricity costs, and ensuring your power supply can deliver enough current.
This calculator works for DC and pure resistive AC loads. For AC circuits with capacitors or inductors, you must use impedance (Z) instead of resistance and account for phase angles; this tool does not handle those complexities.
The calculator ignores the redundant entry and uses the two values that solve consistently. If all three are contradictory (e.g., V=10, I=1, R=20), the tool displays '—' to warn you of an error.
SI prefixes make numbers readable: milli (m) = 0.001, kilo (k) = 1000, mega (M) = 1,000,000. So 1.2k ohms = 1200 ohms, and 0.12mA = 0.00012 amps. The calculator auto-converts large or tiny numbers for clarity.
Yes. This calculator runs entirely in your browser. Your values are not sent to any server, stored, or logged. Your calculations are completely private.