Enter any two parameters (V, A, Ω, W) - the remaining two will be calculated automatically
Voltage U (V)
Current I (A)
Resistance R (Ω)
Power P (W)
💡 Fill exactly 2 fields (leave others empty), then click "Calculate"
Calculated Results
Step-by-Step Derivation
Ohm's Law Formulas
U = I × R (Voltage = Current × Resistance)
P = U × I (Power = Voltage × Current)
P = I² × R = U² / R (Power variations)
Ohm's Law and the power formula form the foundation of DC circuit analysis. Given any two of the four parameters (U, I, R, P), the other two can be determined.
⚠Enter exactly two parameters (leave the rest empty). Power is in watts (W). Division by zero is handled automatically.
What is Ohm's Law?
Ohm's Law, formulated by German physicist Georg Ohm in 1827, is one of the most fundamental laws in circuit theory. It reveals the quantitative relationship between voltage, current, and resistance in resistive circuits and serves as the basis for all circuit analysis and design.
U = I × R
Voltage equals current multiplied by resistance. To maintain a larger current through a fixed resistance, a larger voltage must be applied.
I = U / R
Current equals voltage divided by resistance. For a fixed voltage, smaller resistance leads to larger current.
R = U / I
Resistance equals voltage divided by current. This is the basic method for measuring resistance (voltammetry).
P = U × I
Electrical power equals voltage times current. Variations P = I²R and P = U²/R are used for resistor power rating selection.
💡 Example: Given U = 12V, R = 4Ω. Calculate I = 12/4 = 3A. Power P = 12×3 = 36W. Verify: P = I²R = 3²×4 = 36W, P = U²/R = 12²/4 = 144/4 = 36W. All three formulas agree.
Ohm's Law states that the current through a conductor between two points is directly proportional to the voltage across the two points, and inversely proportional to the resistance. Formula: I = U/R or U = IR. It is the most fundamental law in circuit analysis.
How do I calculate power using Ohm's Law?▼
Electrical power P = UI. Combined with Ohm's Law U = IR, we derive P = I²R or P = U²/R. Choose the appropriate formula based on which two parameters you know.
Does Ohm's Law apply to all circuits?▼
Ohm's Law applies to linear resistive circuits where resistance is constant (e.g., metal conductors). For nonlinear components like diodes or transistors, the V-I characteristic is not linear, so Ohm's Law cannot be directly applied; differential resistance must be used.
How do I choose the right resistor value in practice?▼
Use R = U/I. Determine your circuit voltage and desired current, then compute resistance. Also consider power rating P = I²R to ensure actual power does not exceed 60-70% of the resistor's rated power to prevent overheating.
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