Ohm's Law Calculator
Free online ohm's law calculator. No sign-up, no installation. Runs entirely in your browser.
Calculate Voltage, Current, Resistance & Power
What is Ohm's Law?
Ohm's Law is a fundamental principle in electrical engineering that describes the relationship between voltage, current, and resistance in an electrical circuit. The law states that the current flowing through a conductor is directly proportional to the voltage applied across it and inversely proportional to its resistance.
The primary equation is: V = IR (Voltage = Current × Resistance). This relationship holds true for most conductors under normal conditions and is essential for analyzing and designing electrical circuits.
How to Use This Calculator
- Enter any two electrical values: voltage (V), current (I), resistance (R), or power (P)
- Select the appropriate unit prefix for each value (standard, milli, kilo, or mega)
- Click the "Calculate" button (or press Enter) to compute the missing values
- Review the calculated results, the formulas used, and the circuit diagram
- Click "Clear" to reset all fields and start a new calculation
Common Use Cases
- Electronics Design: Calculate required component values for circuits
- Electrical Safety: Determine safe voltage and current levels for devices
- Power Analysis: Understand energy consumption and efficiency
- Troubleshooting: Diagnose circuit problems and test components
- Educational Learning: Understand fundamental electrical principles and relationships
Frequently Asked Questions
What is the difference between voltage and current?
Voltage is the electrical potential difference, measured in volts (V), while current is the flow of electric charge, measured in amperes (A). Think of it like water in a pipe: voltage is the pressure pushing the water, and current is the actual flow rate of the water.
How is power calculated in circuits?
Power is the rate at which electrical energy is consumed or produced. It can be calculated using three equivalent formulas: P = VI (voltage × current), P = I²R (current squared × resistance), or P = V²/R (voltage squared ÷ resistance). All three formulas are mathematically equivalent.
What do the unit prefixes mean?
Prefixes are used to scale units for larger or smaller values: milli (m) = 0.001 (1/1000), kilo (k) = 1,000, and mega (M) = 1,000,000. For example, 5 kΩ means 5,000 Ω, and 500 mA means 0.5 A. Using prefixes makes it easier to read and write very large or very small numbers.
Why do I need to enter exactly two values?
Ohm's Law and its derived equations form a system where any two of the four values (V, I, R, P) uniquely determine the other two. With fewer than two values, the system has infinite solutions; with all four, the system is overdetermined.
Can I use this calculator for AC circuits?
This calculator is designed for DC (direct current) circuits where resistance is constant. For AC (alternating current) circuits, you would need to account for impedance, which includes reactance from capacitors and inductors, making the calculations more complex.
What happens if I get a calculation error?
The calculator validates your inputs and will display an error message if something is wrong. Common issues include: entering fewer or more than two values, entering zero or negative numbers, or entering values that create mathematical impossibilities. Check your inputs and try again.