Ohm's Law Calculator
Solve for voltage (V), current (I), resistance (R), or power (P) by entering any two known values. Supports all Ohm's Law and power formula combinations. No signup, runs entirely in your browser.
Tips for Circuit Calculations
Series resistors
In a series circuit, total resistance is R₁ + R₂ + R₃. Use the total resistance in this calculator to find current and voltage for the whole circuit.
Parallel resistors
In parallel: 1/R_total = 1/R₁ + 1/R₂. Calculate the equivalent resistance first, then use it here to find total current and power draw.
Power dissipation
When sizing a resistor, calculate the power it will dissipate using P = I²R. Choose a resistor rated for at least twice that power to prevent overheating.
Milli and kilo prefixes
Convert before entering values: 10 mA = 0.01 A, 4.7 kΩ = 4700 Ω, 5 mW = 0.005 W. All inputs must be in base SI units.
Frequently Asked Questions
What is Ohm's Law?
Ohm's Law states that the voltage across a conductor is directly proportional to the current flowing through it: V = I × R. This holds for ohmic materials (resistors) under constant temperature conditions.
What equations does the calculator use?
The calculator uses: V = IR, I = V/R, R = V/I, and the power equations P = VI, P = I²R, and P = V²/R. It automatically selects the right formula based on which two values you provide.
What are the units?
Voltage (V) is in Volts, Current (I) in Amps (A), Resistance (R) in Ohms (Ω), and Power (P) in Watts (W). Use consistent SI units for accurate results.
Does Ohm's Law apply to all components?
No. Ohm's Law applies only to ohmic (linear) components like resistors. Diodes, capacitors, inductors, and transistors are non-ohmic — their V-I relationship is non-linear.
How do I solve for power if I only know V and R?
Select "P" as the solve-for variable and enter V and R. The calculator uses P = V²/R. Similarly, if you know I and R, it uses P = I²R.
Is my data stored?
No. All calculations run locally in your browser. No data is sent to any server.