Ohm’s Law Calculator – Solve Voltage, Current, Resistance And Power
This Ohm’s Law Calculator gives you a fast way to move between voltage, current, resistance and power for simple DC circuits. The main solver tab lets you enter any two known quantities and instantly receive the remaining two. The additional tabs focus on power, voltage, current and resistance so you can jump straight to the calculation that matches your task.
Core Ohm’s Law And Power Formulas
Ohm’s Law describes how voltage, current and resistance interact in a circuit branch:
- V = I × R (voltage in volts)
- I = V ÷ R (current in amps)
- R = V ÷ I (resistance in ohms)
When you include power, a few additional identities are useful:
- P = V × I
- P = I² × R
- P = V² ÷ R
The calculator uses these expressions to keep every result internally consistent and to show you how different forms of the sameationship produce the same outcome.
Using The Ohm’s Law Solver Tab
The general solver tab is a good starting point. Enter any two known values from V, I, R or P and the tool will compute the remaining ones. For example, if you know a 12 V supply and a 220 Ω resistor, the calculator can determine current and power dissipation in that resistor. If you instead know power and resistance, you can recover the corresponding current and voltage.
This is especially helpful when you are selecting resistor values, checking whether a part will overheat or verifying that a circuit will not exceed the ratings of a power supply or trace.
Focused Tabs For Power, Voltage, Current And Resistance
While the main solver can handle every combination, the dedicated tabs streamline common tasks:
- Power tab – Uses V, I and R to calculate power and suggests a minimum wattage rating.
- Voltage tab – Solves for voltage from current and resistance or from power plus one other value.
- Current tab – Solves for current from voltage and resistance or from power and voltage or resistance.
- Resistance tab – Solves for resistance from voltage and current or from power and voltage or current.
These narrower views are convenient during design or troubleshooting when you already know which quantity you want to solve for and you want a clean layout focused on that goal.
Combining This Calculator With Other Tools
For more complex electronics planning, you can use this page alongside other tools on this site. A Resistor Calculator helps you combine series and parallel values or decode color bands, while a Voltage Drop Calculator can show how long cable runs affect supply voltage in low-voltage systems.
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Frequently Asked Questions
Common questions Ohm’s Law, AC/DC assumptions, power ratings, and unit handling in the calculator.
In the main Ohm’s Law solver, you must enter at least two values among voltage (V), current (I), resistance (R), and power (P). The calculator derives the remaining quantities using the standard formulas. If you enter more than two inputs and they conflict, the results may not reflect real circuit behavior, so it is best to start with the two mostiable measurements.
All quantities use standard base SI units: volts (V) for voltage, amps (A) for current, ohms (Ω) for resistance, and watts (W) for power. You may manually convert milliamps, kilohms, or otheres before entering values, or simply type their equivalent base-unit values directly.
This tool assumes simple DC conditions or the RMS equivalents of AC signals without reactive components. In AC circuits containing inductors or capacitors, impedance and phase shift must be considered, and a more advanced analysis is required. For basic low-frequency resistive loads, the results remain a useful approximation.
The power-related tabs compute the wattage dissipated in a resistor and then suggest a minimum part rating above that value. In practice, most designers add extra margin for temperature rise, enclosure heating, and long-termiability. Treat the suggested rating as a baseline, not an absolute requirement.