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Ohm's Law Calculator
Supply any two known electrical parameters—Voltage (V), Current (I), Resistance (R), or Power (P)—to calculate the missing values and view the exact equations used.
Enter Any Two Known Values
Fill in exactly two fields and leave the other two empty.
Circuit Calculation Result
Voltage (V)
12 V
Current (I)
3 A
Resistance (R)
4 Ω
Power (P)
36 W
Derived Equations Used:
I = V ÷ R = 12 ÷ 4 = 3 A | P = V² ÷ R = 144 ÷ 4 = 36 W
Ohm's Law & Electrical Power Formulas
Voltage (V): V = I × R = P ÷ I = √(P × R)
Current (I): I = V ÷ R = P ÷ V = √(P ÷ R)
Resistance (R): R = V ÷ I = V² ÷ P = P ÷ I²
Power (P): P = V × I = I² × R = V² ÷ R
Current (I): I = V ÷ R = P ÷ V = √(P ÷ R)
Resistance (R): R = V ÷ I = V² ÷ P = P ÷ I²
Power (P): P = V × I = I² × R = V² ÷ R
Example: A 12 V battery is connected across a 4 Ω resistor. Find the current and power dissipated:
Current (I) = V ÷ R = 12 ÷ 4 = 3 A
Power (P) = V × I = 12 × 3 = 36 W
Frequently Asked Questions
Ohm's Law states that the electric current (I) flowing through a metallic conductor is directly proportional to the potential difference or voltage (V) across its ends, provided physical conditions like temperature remain constant: V = I × R.
Enter any two known positive values (for example, Voltage V = 12 and Resistance R = 4) and leave the other two fields blank. Click "Calculate Ohm's Law" to compute the remaining two quantities.
Voltage (V) is measured in Volts (V), Current (I) in Amperes (A), Resistance (R) in Ohms (Ω), and Electrical Power (P) in Watts (W).
Combining Joule's power equation (P = V × I) with Ohm's Law (V = I × R) yields three equivalent power formulas: P = V × I, P = I² × R, and P = V² / R.
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