Ohm's Law Calculator

Enter any two values to solve instantly. Includes unit conversions, circuit visualization, and Show Work.

How to Use

  1. Enter any two values (Voltage, Current, Resistance, or Power).
  2. Select the correct units (mA, kΩ, etc.).
  3. Use “Solve For” to force a specific output if desired.
  4. Open “Show Work” to see formulas and steps.
Circuit Lab View
Visual feedback: current flow + heat (power dissipation).
V
—
I
—
R
—
P
—
Risk: —
Battery V Resistor (R) R Drag: V handle (battery) or R handle (resistor) Solve V Solve I Solve R Solve P Visuals scale with current (arrow thickness & flow speed) and power (heat overlay).
Inputs & Settings
Type any two values. Use “Solve For” + locks for guided solving.
Common: 5V, 12V, 14.4V, 120V, 230V
Examples: 20mA LED, 2A load, 10A+ automotive
Tip: 0Ω implies a short circuit in an ideal model
Use for resistor heating / load sizing
Quick Adjust
12 V
10 Ω

Tip: Sliders are for quick “what-if” testing. Use unit dropdowns for mA/kΩ scaling.

Show Work (step-by-step)
—
Work is shown in base units (V, A, Ω, W) for clarity and consistency.

Ohm's Law Formulas

Quick answer: Ohm's Law relates voltage, current, and resistance: V = I × R.

Enter any two values to solve the other variables.

  • Voltage: V = I × R
  • Current: I = V ÷ R
  • Resistance: R = V ÷ I
  • Power: P = V × I = I² × R = V² ÷ R
Where V = volts, I = amps, R = ohms, P = watts.

FAQ

How do I calculate a resistor for an LED?

Use R = (V_supply − V_forward) / I. Example: 5V supply, 2V LED, 20mA → R = 150Ω.

What happens if resistance doubles?

If voltage stays constant, current halves because I = V / R.

Why does Ohm's Law fail with diodes?

Diodes are non-ohmic. Their V–I curve is non-linear due to junction physics.

What does “0Ω” mean?

In an ideal model it implies a short circuit and very high current. Real sources and wiring limit current, but fusing/heat becomes critical.

Tool Info

Last updated:

Updates may include UI improvements, unit support, and calculation edge-case handling.