Ohms Law Calculator
Calculate voltage, current, resistance, or power using Ohms Law.
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How It Works
Ohm Law states V = I × R. Voltage equals Current times Resistance. Enter any two values to calculate the third. Power is also calculated: P = V × I.
Formula
V = I x R, P = V x IQuick Reference
Common calculations — results you can verify instantly.
12V, 100Ω
I = V/R
0.12A (120mA)
5A, 10Ω
V = I×R
50V
120V, 10A
P = V×I
1200W (1.2kW)
LED: 5V, 20mA
R = (5-2)/0.02
150Ω resistor
Tips & Shortcuts
Memorize the power triangle: P=VI, V=P/I, I=P/V.
Resistors in series add: R_total = R1+R2+R3.
Resistors in parallel: 1/R_total = 1/R1 + 1/R2.
Double the voltage — double the current (if resistance stays constant).
Common Mistakes
Mixing units — using mA with ohms and volts
Convert milliamps to amps first (÷1000). V = I(A) × R(Ω).
Applying Ohm Law to non-ohmic components like LEDs
Ohm Law applies to resistive components only. Diodes and LEDs are non-ohmic.
Frequently Asked Questions
V = I × R = 0.5 × 100 = 50 volts.
P = V × I = I²R = V²/R. Power is in watts.
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