How this calculation works
Ohm’s law relates voltage, current and resistance for a component whose resistance is constant under the conditions being considered. Current in amperes multiplied by resistance in ohms gives volts.
Voltage = current × resistanceA worked example
A current of 2 A through 10 Ω corresponds to 20 V.
Good to know
An ideal DC relationship. Real components may change resistance with temperature or behave nonlinearly. Not an electrical installation design tool.
The same resistance turns current into a voltage drop
Across a fixed 10 Ω resistor, 1 A corresponds to 10 V and 2 A to 20 V. The proportional relationship holds because resistance is kept constant. Changing the material or its conditions can change that resistance and therefore the relationship.
Combining V = IR with P = VI gives P = I²R for this ideal resistive model. Doubling current at fixed resistance doubles voltage but quadruples dissipated power.
Convert milliamps before multiplying
1,000 mA equals 1 A. If a current is 20 mA, enter 0.02 A, not 20. Paired with 100 Ω, that gives 2 V. A prefix error would change the answer by a factor of one thousand.
Use this for an ideal DC resistance calculation. Components with nonlinear behavior, changing temperature or reactive AC impedance need additional models. The arithmetic does not determine a safe component power rating.
A few questions, answered
Does this solve for current or resistance?
This edition calculates voltage from current and resistance.
Can I use a resistance quoted in kΩ?
Convert it to ohms first: 1 kΩ equals 1,000 Ω.