Ohm's law calculator
Enter any two of voltage, current, resistance and power to get the other two.
Resistance
24Ω
- Power
- 6 W
- Current
- 500 mA Given
- Voltage
- 12 V Given
Method
How this is calculated
V = I · R P = I · V = I² · R = V² / R R = V / I = V² / P = P / I² I = V / R = P / V = √(P / R)
- Assumes
- A linear (ohmic) resistance at DC, or RMS values for a purely resistive AC load. Diodes, LEDs and lamps are not ohmic: their resistance changes with current.
- Units
- Volts, amperes, ohms and watts. Results are shown with SI prefixes (mA, kΩ, mW).
FAQ
Questions
I = V / R = 5 / 1000 = 5 mA, and the resistor dissipates P = V² / R = 25 mW. A 1/10 W part is comfortable at that power.
R = P / I². A motor drawing 20 A while turning 666.67 W into heat has a winding resistance of 666.67 / 20² = 1.67 Ω.
Not directly. An LED's voltage stays close to its forward voltage over a wide current range, so it does not behave as a fixed resistance. Use the LED resistor calculator, which subtracts the forward voltage first.
For a purely resistive load, yes, using RMS voltage and current. With capacitance or inductance in the circuit, replace R with the impedance magnitude and account for phase when working out real power.
Related
Related tools and reading
Next step
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