Ohm’s law calculator

V = I × R · I = V / R · R = V / I. Pick two known values; the third (and DC power) are computed.

V in volts, I in amps, R in ohms, P in watts.
Voltage (V)
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Current (I)
—
Resistance (R)
—
Power (P)
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Quick reference

  • Power triangle: P = V × I = I² × R = V² / R
  • Common units: 1 kΩ = 1,000 Ω; 1 MΩ = 1,000,000 Ω; 1 mA = 0.001 A.
  • LED safety: always use a series resistor — calculate with our LED resistor calculator.