Ohm's Law & Electronics Calculator

Solve V, I, R, P · Decode resistor color codes · LED resistor sizing · Series & parallel combinations

Enter any two known values. The other two are calculated automatically.

V Voltage

I Current

R Resistance

P Power

Formula Reference

V = I × R

I = V / R

R = V / I

P = V × I

P = I² × R

P = V² / R

About Ohm's Law & Electronics Calculations

Ohm's Law

Ohm's Law (V = IR) relates voltage, current, and resistance in a conductor. Combined with the power formula P = VI, you can solve for any unknown given two knowns.

Resistor Color Codes

Resistors use colored bands to indicate their value. 4-band resistors give two significant digits; 5-band resistors give three, offering higher precision. The last band indicates tolerance.

LED Current Limiting

LEDs must have a series resistor to limit current. Too much current destroys the LED; too little makes it dim. Use R = (V_cc − V_f) / I_f for a single LED in series.

Series vs Parallel

Series resistors add directly. Parallel resistors always give a result smaller than the smallest resistor — great for increasing current capacity or fine-tuning values.