Use our interactive Ohm’s Law Calculator to compute voltage, current or resistance instantly. Enter any two values and get a clear, step-by-step explanation.
⚡ Ohm’s Law Calculator
Calculate Voltage (V), Current (I), or Resistance (R) easily using Ohm’s Law.
Voltage is the potential difference across two points in a circuit.
Current is the flow of electric charge through a conductor.
Resistance opposes the flow of current in an electrical circuit.
What is this calculator?
This Ohm’s Law Calculator computes one of the three fundamental electrical quantities — Voltage (V), Current (I), or Resistance (R) — when the other two are known. It uses the basic relation known as Ohm’s Law.
Why you need an Ohm’s Law calculator
Ohm’s Law is a core principle in electronics and electrical engineering used for designing circuits, troubleshooting, and learning. This calculator speeds up routine calculations, prevents manual errors, and provides a clear explanation of the steps for educational use or quick prototyping.
Quick facts
– Ohm’s Law formula: V = I × R.
– Units: Voltage in volts (V), Current in amperes (A), Resistance in ohms (Ω).
– You must enter any two of the three values to compute the third.
Real-life examples
Example 1 — LED resistor selection: You have a 5 V supply and want 20 mA (0.02 A) through an LED. Required resistor = R = V ÷ I = 5 ÷ 0.02 = 250 Ω.
Example 2 — Finding current: A motor has 12 V across it and internal resistance 6 Ω. Current = I = V ÷ R = 12 ÷ 6 = 2 A.
How to use
1. Enter any two values (V, I, or R) in their fields.
2. Click Calculate. The calculator will compute the missing value and show a step-by-step explanation.
3. Use Load Sample to auto-fill example values, or Clear to start over.
Formulas (all variations)
Ohm’s Law can be rearranged depending on which variable is unknown:
V = I × R— Voltage equals current times resistance.I = V ÷ R— Current equals voltage divided by resistance.R = V ÷ I— Resistance equals voltage divided by current.
Some history
Ohm’s Law is named after the German physicist Georg Simon Ohm, who published his work The Galvanic Circuit Investigated Mathematically in 1827. His experiments established the relationship between voltage, current, and resistance and laid the foundation for circuit theory.
Practical tips
– Always check units (convert mA to A before using the formulas).
– Never divide by zero — resistance or current of zero causes invalid results when used as a divisor.
– For circuits with components in series/parallel, compute equivalent resistance first before using this calculator.
– Use the calculator for quick checks, then verify with measurements using a multimeter when working on live circuits.
Frequently Asked Questions
Q: Can I enter values with units like “5V” or “2A”?
A: No — enter numeric values only (e.g., 5 for 5 volts, 0.02 for 20 mA). Convert milli- and kilo- prefixes to base units first.
Q: What happens if I put three values?
A: The calculator will ask you to enter exactly two values. If all three are given, either one may be inconsistent with the others due to measurement error — choose which value to calculate instead.
Q: Is this calculator suitable for AC circuits?
A: This calculator uses the simple resistive Ohm’s Law valid for DC circuits or purely resistive AC circuits. For AC circuits with reactance (inductors/capacitors), use impedance (Z) and phasor methods instead.
Disclaimer
This calculator is provided for educational and quick estimation purposes only. Always verify designs and measurements using proper instruments and safety precautions. The author is not responsible for misuse of calculated values in real-world electrical installations.