Ohm's Law Calculator
Enter any two known values to calculate the other two. The results will update automatically.
Understanding Ohm's Law
This section introduces the fundamental principles of Ohm's law. It provides a foundational understanding of the relationship between voltage, current, and resistance, which is essential before diving into the more complex formulas and applications discussed later.
Ohm's Law states that the current flowing through a conductor between two points is directly proportional to the voltage across the two points. It is one of the most fundamental laws in electronics and electrical engineering.
The primary formula is:
V = I × R
- V is the Voltage, measured in Volts (V).
- I is the Current, measured in Amperes (A).
- R is the Resistance, measured in Ohms (Ω).
The Power Wheel of Formulas
This "Power Wheel" is a comprehensive reference that expands on the basic V=IR formula to include Power (P). It organizes all 12 derived formulas, allowing you to easily find the correct equation to solve for any unknown variable when you know two others. It is an invaluable tool for quick reference.
Voltage (V)
I × R
P / I
√(P × R)
Current (I)
V / R
P / V
√(P / R)
Resistance (R)
V / I
P / I²
V² / P
Power (P)
V × I
I² × R
V² / R
Interactive Visualization
This chart provides a dynamic way to see Ohm's law in action. By adjusting the resistance with the slider, you can observe how the linear relationship between voltage and current changes. This helps to build an intuitive understanding of how these electrical properties are interconnected.
Ohm's Law Calculator for Parallel Circuits and Power Checks
An ohm's law calculator for parallel circuits uses one common branch voltage, each branch resistance, and the sum of all branch currents. For finite resistors, 1/Req = Σ(1/Rn), so the equivalent resistance must be lower than the smallest branch value. Treat an open branch as infinite resistance and a zero-ohm branch as a short, not an ordinary input. The source current is Σ(V/Rn), and every resistor needs voltage and power ratings above its calculated stress with thermal margin.
- Apply branch voltage: solve
V = IRindependently for each parallel path. - Add the currents: total source current equals the arithmetic sum of branch currents.
- Invert conductance: calculate equivalent resistance from reciprocal values without rounding early.
- Rate each resistor: verify
P = V²/R, tolerance, temperature, and pulse loading. - Measure resistance safely: de-energize the network and discharge stored energy before probing.
