How to use Ohm's Law Calculator
- 1
Open the Ohm's Law Calculator
Go to tools.slaytic.com and open the Ohm's Law Calculator. No sign-up or account required.
- 2
Enter any two values
Supply two of voltage, current and resistance, using amps rather than milliamps.
- 3
Read the third value and the power
The remaining quantity is calculated, along with the power in watts.
How this works in your browser
The calculator rearranges a single relationship, voltage equals current times resistance, according to which two values you supplied: dividing voltage by resistance gives current, dividing voltage by current gives resistance, and multiplying current by resistance gives voltage. Power is then computed as voltage times current. Showing power alongside the answer is deliberate rather than decorative, because it is the figure that determines whether a component survives: a resistance value can be perfectly correct while the component chosen to provide it burns out. The relationship holds for resistive DC circuits, and the calculation runs entirely in your browser.
Ohm's Law Calculator vs. traditional online converters
| Feature | Ohm's Law Calculator (in-browser) | Traditional online converters |
|---|---|---|
| File upload required | No - never leaves your device | Yes - file is sent to a server |
| Processing queue | None - starts instantly | Often, especially at peak times |
| Watermark on output | Never | Common on free plans |
| Usage limits | None - free, unlimited use | Often capped per day or file size |
| Works offline once loaded | Yes, for most tools | No - requires a live connection |
| Account required | No | Often, for anything beyond a trial |
Who uses Ohm's Law Calculator
Choosing resistor values
Work out the resistance and wattage needed to limit current through a component.
Power supply sizing
Check the current a circuit will draw at a given voltage.
Troubleshooting a circuit
Verify whether measured values match what the components should produce.
Electronics study
Check calculations while learning the relationships between the quantities.
Frequently asked questions
What is Ohm’s Law?
A fundamental electronics relationship stating that voltage equals current multiplied by resistance, for simple resistive circuits.
How is power calculated?
Power in watts equals voltage multiplied by current, calculated automatically once voltage and current are known.
Does this account for AC circuits with reactance?
No, this calculates basic DC (or simple resistive) Ohm’s Law relationships only.
How do I pick a resistor for an LED?
Subtract the LED’s forward voltage from your supply voltage, then divide by the current you want through it. A 5V supply with a 2V LED at 20 milliamps needs 3 volts divided by 0.02 amps, which is 150 ohms. Then check the power figure, since it tells you the wattage rating the resistor needs.
Why does the power figure matter?
Because a resistor with the right resistance but too low a power rating will overheat and fail, sometimes dramatically. Quarter-watt resistors are the common default, so anything approaching that number needs a physically larger component.
Should I enter current in amps or milliamps?
Amps, so 20 milliamps is 0.02. Mixing units is far and away the most common source of results that are wrong by a factor of a thousand, and the numbers look plausible enough that it is easy to miss.
Why does this not apply to AC circuits?
Because capacitors and inductors oppose alternating current in a way that depends on frequency, called reactance, which the simple relationship does not model. For AC you need impedance rather than plain resistance.