Science & Engineering

Ohm's Law Calculator

Calculate voltage, current, or resistance using Ohm's Law (V=IR).

Ohm's Law is the foundation of electrical engineering. Given any two of voltage (V), current (I), or resistance (R), this calculator solves for the third. Essential for electronics hobbyists, electricians, and engineering students.

Enter your numbers

Solve For

Value 1

Value 2

Results update as you change the inputs. Calculations run in your browser.

Voltage

24.000 V

power: 288.00 W
formula: V = I × R = 12 × 2

See the formula

Formula and method

V = I × R (Ohm's Law)

Ohm's Law states that voltage equals current times resistance. The three derived formulas are V=IR, I=V/R, and R=V/I. Power is calculated as P = V × I = I² × R = V²/R.

Worked examples

LED resistor calculation (5V, 20mA)

Solve For:: Resistance (R)
Value 1:: 5
Value 2:: 0.02

Resistance (Ohms): 250.00 Ω

12V battery, 6Ω resistance

Solve For:: Current (I)
Value 1:: 12
Value 2:: 6

Current (Amps): 2.0000 A

Assumptions and limits

Linear (ohmic) component
DC circuit
Room temperature

This tool provides an educational estimate. Rules, rates and personal circumstances can change the answer. Review the assumptions before relying on a result. Report a correction.

Common mistakes to avoid

Mixing up units — current is in Amps, not milliamps. A 100mA current is 0.1A.
Applying Ohm's Law to non-ohmic components — diodes and LEDs have non-linear I-V curves.
Forgetting that resistance increases with temperature in most metals (positive temperature coefficient).

Frequently asked questions

What is Ohm's Law in simple terms?

Voltage = Current × Resistance. If you push more voltage through a wire (pressure), more current flows. A higher resistance is like a narrower pipe — same voltage produces less current. It's the fundamental relationship in all electronics.

How do I calculate power consumption?

Power (watts) = Voltage × Current. A 12V device drawing 2A uses 24W. Or use P = V²/R = I²R. A 60Ω resistor on 12V draws 12²/60 = 2.4W.

What is a safe current for a human body?

Just 10mA (0.01A) through the chest can cause heart fibrillation. 100mA is often lethal. Household voltage (120-240V) can easily push fatal current through the body's ~1,000Ω skin resistance. Always treat electrical systems with respect.