Calculadora de Ohm — Lei de Ohm (Cálculo de Ohms)
Calcule tensão, corrente, resistência e potência
Required Parameters
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Quick Answer
Ohm's Law: V = I × R. Enter any two values to solve voltage, current, resistance, or power (P = V × I) for DC resistive circuits.
Ohms Calculator
Use this free ohms calculator to solve Ohm's law instantly: enter any two of voltage (V), current (I), and resistance (R) — the tool computes the third plus power (P) when relevant.
Quick start: Pick what you want to find (Voltage, Current, Resistance, or Power), enter the other two values, and read the result.
Ohms calculator formulas
| Find | Formula |
|---|---|
| Voltage | V = I × R |
| Current | I = V / R |
| Resistance | R = V / I |
| Power | P = V × I = I²R = V²/R |
The Ohm's law triangle
Cover the value you want:
- V covered → multiply I × R
- I covered → divide V ÷ R
- R covered → divide V ÷ I
Worked example
12 V supply, 470 Ω resistor:
- I = 12 / 470 = 25.5 mA
- P = 12 × 0.0255 = 0.31 W → use a 1/2 W resistor minimum
Unit tips
- mA → A: divide by 1,000 (250 mA = 0.25 A)
- kΩ → Ω: multiply by 1,000 (4.7 kΩ = 4700 Ω)
- Engineering shorthand: 4k7 = 4700 Ω, 10u = 10 µA
When Ohm's law does not apply
- LEDs and diodes — non-linear Vf, not constant R → LED resistor calculator
- AC with L or C — use impedance Z, not R → Reactance calculator
Related tools
- Ohm's Law Calculator — same engine, Ohm's law focused entry
- Voltage divider
- Parallel resistor calculator
- Electrical power calculator
Design Notes
Ohm's Law applies precisely to Ohmic materials where resistance remains constant regardless of current or voltage. In practical engineering, resistors heat up when dissipating power (P = I²R), which can alter their resistance (Temperature Coefficient of Resistance). Always verify that your calculated power dissipation is below the resistor's actual wattage rating (typically leave a 50% margin).
Common Mistakes
- 1
Mixing up units: Forgetting to convert milli-amps (mA) to Amps (A) before calculating.
- 2
Ignoring power dissipation: A 1/4W resistor will burn up if your calculation yields 0.5W, even if the resistance is correct.
- 3
Applying it to non-linear components: Ohm's law does not directly apply to diodes, LEDs, or transistors which have dynamic resistance.
Engineering Handbox
1. Identify knowns: V = 12, R = 470 2. Use Formula: I = V / R 3. Calculate: I = 12 / 470 = 0.02553 A (25.53 mA) 4. Calculate Power: P = 12 × 0.02553 = 0.306 W
Knowledge Base
Quais são as 3 fórmulas da Lei de Ohm?
V = I × R (Tensão), I = V / R (Corrente) e R = V / I (Resistência). Rearranjos da relação descoberta por Georg Ohm em 1827.
Como uso o triângulo de Ohm?
Coloque V no topo, I embaixo à esquerda e R embaixo à direita. Tape a variável desejada: V → I×R, I → V÷R, R → V÷I.
Posso usar para corrente alternada (CA)?
Apenas para cargas puramente resistivas. Com capacitores ou indutores, substitua R por impedância Z = √(R²+X²).
Como calculo a potência?
P = V×I, P = I²×R ou P = V²/R. Escolha com base nas duas variáveis conhecidas.
Por que não funciona para LEDs?
LEDs são dispositivos não-lineares com queda de tensão fixa. Use nossa calculadora de resistor para LEDs.
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