Calculadora da Lei de Ohm
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
Formula
V = I·R
About this calculator
The Ohm's Law Calculator allows you to quickly determine voltage (V), current (I), or resistance (R) in an electrical circuit. Ohm's law, expressed as V = I·R, states that the voltage between two points of a conductor is directly proportional to the current flowing through it, with the constant of proportionality being the electrical resistance. This tool is essential for students, technicians, and engineers working with electrical circuits.
The operation is simple: you enter two known values among voltage (in volts), current (in amperes), and resistance (in ohms), and the calculator provides the third value. For example, if you know voltage and current, resistance is calculated as R = V / I. If you know voltage and resistance, current is I = V / R. And with current and resistance, voltage is V = I · R. The tool also supports unit conversion with prefixes like milli, kilo, and mega.
This calculator is useful in various practical situations: sizing resistors in electronic projects, checking power consumption of appliances, analyzing simple circuits in physics labs, and troubleshooting voltage drop in electrical installations. For instance, when designing an LED circuit, you need to calculate the current-limiting resistor using Ohm's law.
Important precautions: Ohm's law is valid only for ohmic materials whose resistance remains constant with temperature and voltage. In components such as diodes or incandescent bulbs, resistance varies, and the law does not apply linearly. Additionally, always use consistent units (volts, amperes, ohms) and verify that the entered values are realistic to avoid damaging components.
Frequently asked questions
What is Ohm's Law?
Ohm's Law states that the voltage (V) across a conductor is equal to the product of the current (I) and resistance (R), i.e., V = I·R. It describes the linear relationship between these quantities in conductive materials.
How do I use the calculator?
Enter two known values (voltage, current, or resistance) and the calculator will provide the third. Select the appropriate units and click Calculate.
Does Ohm's Law apply to all components?
No. It applies only to ohmic materials, such as fixed resistors. Components like diodes, transistors, and incandescent bulbs have non-linear behavior.
What is the difference between DC and AC in Ohm's Law?
In direct current (DC), Ohm's law is applied directly with constant values. In alternating current (AC), impedance (resistance + reactance) is used instead of pure resistance.
What if the result is too high or too low?
Check that the units are correct (e.g., not confusing milliamperes with amperes). Ensure the entered values are realistic for the circuit in question.