Ohm’s law calculator

Worked example

Across a 1 kΩ resistor at 5 V, I = V / R = 5 V / 1000 Ω = 0.005 A = 5 mA. Power in that resistor is P = V × I = 0.025 W = 25 mW.

Rearrange V = I × R to find voltage, or R = V / I to find resistance. Enter current in amperes: 5 mA = 0.005 A. Zero and out-of-range values cannot be used in this positive-value calculator.

How the estimate works

Basis: Ohm’s law, V = I × R, with consistent SI units, for an ideal, steady-state DC ohmic resistance. Real components may change resistance with temperature. This is arithmetic, not a circuit simulation or component rating check. These idealized calculations do not check every real-world limit. Work with safe low voltages and verify your design independently.