Ohm's Law Calculator
Enter any two of voltage, current and resistance to compute the third via V = I·R.
Input Data
Results
At a glance:Ohm's law states that the current through a conductor between two points is proportional to the voltage across it: V = I·R, where V is voltage (V), I current (A) and R resistance (Ω). Rearranged: I = V/R, R = V/I. It holds for ohmic materials (constant R, e.g. metals at fixed temperature). This tool lets you pick which variable to solve for and enter the other two. Power follows as P = V·I = I²R = V²/R. Ohm's law is the backbone of circuit design, from simple dividers to complex networks (combined with Kirchhoff's laws).
Formula
V = I·R
I = V/R
R = V/I
How to Use
- Select which quantity to solve for (V, I or R).
- Enter the other two values.
- The calculator returns the result.
Case Studies
LED resistor
Supply 5 V, LED drops 2 V, wants 20 mA.
R = (5−2)/0.02 = 150 Ω.
Limits current to 20 mA.
FAQ
Does Ohm's law always hold?
Only for ohmic (linear) devices where R is constant. Diodes, transistors and incandescent bulbs (R changes with temperature) are non-ohmic.
How do I find resistance from V and I?
R = V/I. For example 12 V across a device drawing 2 A gives R = 6 Ω.
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References
Content review: Calculatorism Science Team. Results are for reference only; please refer to the relevant authorities for the official figures.