Ohm's Law Calculator Online | V=IR Formula
Calculate voltage, current, or resistance using Ohm's law (V=IR). Enter any two values to find the third.
How to Use
- Select which quantity you want to calculate: Voltage (V), Current (I), or Resistance (R).
- Enter the two known values in their respective fields.
- Click 'Calculate' to instantly compute the unknown value.
- The tool also calculates power (P = V × I) automatically.
- Use SI prefixes if needed: mA (milliamps) = A × 0.001, kΩ (kilohms) = Ω × 1000.
- To verify: multiply your calculated current by resistance — the result should equal your voltage.
About Ohm's Law
What is Ohm's Law?
Ohm's Law states that the current (I) through a conductor is directly proportional to the voltage (V) across it and inversely proportional to its resistance (R). The formula is V = I × R. Named after German physicist Georg Simon Ohm (1789–1854), it is the most fundamental relationship in electrical engineering, forming the basis of circuit analysis.
The Three Forms of the Formula
Ohm's Law can be rearranged in three ways: V = I × R (voltage equals current times resistance), I = V / R (current equals voltage divided by resistance), and R = V / I (resistance equals voltage divided by current). Knowing any two values allows you to calculate the third. This triangle of relationships is the backbone of all basic circuit calculations.
Power Calculation
Once you know voltage and current, power can be calculated as P = V × I (watts). Combined with Ohm's Law, power can also be expressed as P = I² × R or P = V² / R. These relationships are used to determine heat dissipation in resistors, the efficiency of power supplies, and energy consumption in electrical systems.
Limitations of Ohm's Law
Ohm's Law applies to linear (ohmic) conductors such as metal resistors under constant temperature. It does not apply to non-linear components such as diodes, transistors, and LEDs, which have complex voltage-current relationships. Temperature, frequency, and material properties can all affect whether a material behaves ohmically.
Key Features
- Solve for voltage, current, or resistance with any two known values
- Automatic power (P = V × I) calculation
- Supports decimal and scientific notation input
- Instant results with no page reload required
- Useful for beginners and professionals in electronics
Common Applications
- Sizing resistors in electronic circuits
- Calculating current draw of a device from its voltage and resistance
- Determining required voltage for a given current and load
- Power supply design and component selection
- Educational use in physics and electrical engineering courses