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Calculate voltage, current, resistance, and power using Ohm's Law. Enter any two values to calculate the others.
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Red LED with 12V supply, 20mA forward current, 2V forward voltage
5V power supply with 100Ω load resistor
240V heating element rated at 2000W
12V motor drawing 500mA at rated load
USB device charging at 5V, 2A (fast charge)
8Ω speaker with 50W power rating
Calculate total resistance of resistors connected in series: Rtotal = R1 + R2 + R3 + ...
Calculate total resistance of resistors connected in parallel: 1/Rtotal = 1/R1 + 1/R2 + 1/R3 + ...
Calculate voltage drop in a wire: Vdrop = I × Rwire
Resistance in Ω per 100m at 20°C
Ohm's Law is a fundamental principle in electronics that describes the relationship between voltage, current, and resistance in an electrical circuit. It was named after German physicist Georg Ohm, who published it in 1827.
The law states that the current flowing through a conductor between two points is directly proportional to the voltage across the two points and inversely proportional to the resistance between them.
V = I × R
Calculate the required current-limiting resistor to prevent LEDs from burning out. LEDs have a specific forward voltage and current rating.
Design and analyze power supply circuits, calculate current draw, and determine appropriate component ratings.
Calculate current requirements for DC motors and determine appropriate wire gauges for motor connections.
Match speaker impedance with amplifiers, calculate power delivery, and design proper connections.
⚠️ Always Work Safely with Electricity
The 12 formulas in Ohm's Law calculator are derived from three fundamental relationships:
Derived by combining P = V × I with Ohm's Law
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Tip: These common values can help you quickly test calculations or design circuits. Click any value to insert it into the calculator above.