Ohm's Law Calculator

Solve for voltage, current, or resistance from any two values. Also shows power (watts).

By Konstantin Iakovlev · Updated April 2026 · Source: Khan Academy

A
Ω

Voltage

12.000 V

Current

2.000 A

Resistance

6.000 Ω

All Values

Voltage (V)12.000 V
Current (I)2.000 A
Resistance (R)6.000 Ω
Power (P)24.000 W
FormulaV = I × R

Use the Ohm's Law Calculator above to calculate your results. Enter your values and see instant results — all calculations run in your browser.

Disclaimer: This calculator is for informational purposes only and does not constitute tax, financial, or legal advice. Results are estimates based on the information you provide and current rates. Always consult a qualified tax professional or financial advisor for advice specific to your situation.

How It Works

Engineers, technicians, and hobbyists reach for Ohm's Law whenever a circuit needs to be solved or debugged. Give the tool any two of voltage, current, or resistance, and it returns the third while also reporting the power in watts dissipated by the circuit. As IoT devices and smart home technology continue spreading in 2026, a firm grip on these relationships matters more than ever for clean design and quick troubleshooting.

The math rests on Ohm's Law, V = I * R, which ties voltage (V), current (I), and resistance (R) together, paired with the power formula P = V * I. Supply any two of V, I, or R, and the tool rearranges these equations to find the missing value before going on to compute the power.

Consistent units are non-negotiable here: volts, amperes, and ohms. Two traps catch people regularly. One is mixing up resistance in ohms with conductance in siemens; the other is blurring DC and AC behavior, given that Ohm's Law applies cleanly to DC or to instantaneous AC values. Verifying your inputs before you read the result spares you most calculation errors.

Example: Powering a Smart LED Strip in 2026

  1. 1 Imagine you're designing a smart home lighting system in 2026, and you have an LED strip that requires 12V and has a total resistance of 24 Ohms. You want to know the current it draws and the power it consumes.
  2. 2 Input Voltage (V) = 12V, Resistance (R) = 24 Ohms. The calculator will use I = V / R and P = V * I.
  3. 3 Calculated Current (I) = 0.5 Amperes, Calculated Power (P) = 6 Watts.
  4. 4 This means your 12V LED strip will draw 0.5 Amperes of current and consume 6 Watts of power. This information is vital for selecting the correct power supply unit (PSU) and ensuring your circuit design can safely handle the load, preventing overheating or component failure, which is especially important for the longevity of smart home devices.

Source: Khan Academy · Last updated: April 2026

Frequently Asked Questions

What is Ohm's Law?
Ohm's Law states that voltage (V) equals current (I) times resistance (R): V = IR. You can rearrange to find any value: I = V/R or R = V/I. It is the foundational equation for electrical circuits.
How do you calculate watts from volts and amps?
Power (watts) = voltage x current. For a 120V outlet drawing 10 amps: 120 x 10 = 1,200 watts. You can also calculate: P = I²R or P = V²/R.
What is the resistance of a 60-watt light bulb?
At 120V: R = V²/P = 120²/60 = 240 ohms. The current draw is I = P/V = 60/120 = 0.5 amps. Note that actual resistance varies with filament temperature.

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