Engineering
Ohm's law calculator
Pick which quantity to solve for — voltage (V), current (I), resistance (R), or power (P). Enter the other two, and the calculator returns all four values plus dissipated power.
Formula
Ohm's law (V = IR) is the most fundamental relation in DC circuit analysis. Combined with the power formula (P = VI = I²R = V²/R), it lets you solve any two-terminal resistive problem with just two known values.
The calculator handles all four solve directions. For solving P, you can provide V and I directly. For other cases, the third and fourth quantities are computed automatically.
This applies to pure DC circuits with linear resistors. For AC, you'd use impedance (which is complex) instead of resistance. For non-linear components (diodes, transistors), Ohm's law is only an approximation.
Examples
- 01I = 0.5 A through R = 24 Ω→ V = 12 V, P = 6 W
- 02V = 9 V across R = 470 Ω→ I = 0.019 A = 19 mA, P = 0.172 W
- 03V = 120 V drawing I = 5 A→ R = 24 Ω, P = 600 W (heater)
- 04100 W bulb at 120 V→ I = 0.833 A, R = 144 Ω (cold)
FAQ
- Only for purely resistive AC circuits. For inductors and capacitors you use impedance Z (complex number, frequency-dependent) instead of resistance R. The formula then becomes V = IZ.