Voltage / Ohm's Law Calculator
Compute voltage, current or resistance from Ohm's law V=I·R (given two, find the third). Supports unit prefixes (m/k/M).
Input Data
Results
At a glance:Ohm's law: V = I·R. Given any two of voltage V (volts), current I (amperes) and resistance R (ohms), solve for the third: V=I·R, I=V/R, R=V/I. This tool assumes an ideal linear resistor; real components may be non-linear. Related to power P=V·I. A fundamental tool for physics and electronics.
Formula
V = I·R; I = V/R; R = V/I.
$$V = I\,R, \quad I = \frac{V}{R}, \quad R = \frac{V}{I}$$How to Use
- Select which quantity to solve for (V, I or R).
- Enter the other two values (with optional m/k/M prefix).
- The tool returns the result and a short note.
Case Studies
Basic circuit
A 10 Ω resistor carries 2 A → V = I·R = 2×10 = 20 V.
To push 2 A through 10 Ω needs a 20 V source.
Power dissipated P=V·I = 40 W.
Finding resistance
A 12 V supply drives 0.5 A → R = V/I = 12/0.5 = 24 Ω.
Useful for sizing current-limiting resistors.
LED resistor = (Vsupply − Vled)/Iled.
FAQ
What is Ohm's law?
V=I·R: voltage equals current times resistance. Given any two of V, I, R, solve for the third.
Does it work for all components?
Only for Ohmic (linear) resistors where V and I are proportional. Diodes, transistors and incandescent bulbs are non-linear and need their own I-V curves.
How do unit prefixes work?
m = 10⁻³, k = 10³, M = 10⁶. Enter e.g. 2 k for 2000 Ω or 5 m for 0.005 A. The tool parses them automatically.
How is it related to power?
Power P=V·I; with Ohm's law also P=I²R=V²/R. Combine them to size resistors and check dissipation.
Related Tools
References
Content review: Calculatorism Physics Team. Results are for reference only; please refer to the relevant authorities for the official figures.