Ohm's Law Calculator — V, I, R, P
Enter any two of voltage, current, resistance or power to instantly get the rest, with the formulas used.
🔒 Runs entirely in your browser. Your input and output are never sent to a server or stored — fully private.
Fill in any two fields; the other two are calculated.
About this tool
This Ohm's Law calculator works out voltage, current, resistance and power from one another: enter any two of the four values and it instantly fills in the remaining two, showing the exact formulas it used. It is handy for sizing a resistor, checking whether a component can handle the wattage, or simply learning how V, I, R and P relate. All the math runs in your browser, so your numbers never leave your device.
Frequently asked questions
Which two values do I need to enter?
Any two of voltage (V), current (I), resistance (R) and power (P) are enough. From the pair you give, the calculator applies Ohm's law (V = I × R) together with the power formula (P = V × I) to derive the other two, so you never have to rearrange the equations yourself.
What units should I use for the inputs?
Use the base SI units for a consistent result: volts for voltage, amperes for current, ohms for resistance and watts for power. If you are working in milliamps or kilohms, convert them first (for example 1 mA is 0.001 A and 1 kΩ is 1000 Ω) so the answer comes out in volts and watts.
Are my values sent anywhere?
No. Every calculation happens locally in your browser using JavaScript, so the numbers you type are never uploaded to or stored on a server.