About OhmCalc

What this is

OhmCalc is a collection of the calculations electronics engineers, technicians, students and hobbyists reach for constantly: decoding resistor bands and SMD markings, sizing an LED dropper, working an Ohm's law problem, checking whether a divider will sag under load, reading a capacitor code, and sizing a PCB trace for current.

None of these are hard calculations. What is hard is finding a page that does them without a full-screen newsletter prompt, a cookie wall, three seconds of layout shift, and a result that quietly ignores the case you actually had.

Design principles

• Correct in the corners. Six-band resistors with temperature coefficients, EIA-96 codes that look like three-digit codes, dividers under load, traces where voltage drop binds before temperature does. The edge cases are the reason a calculator exists at all.
• Real components, not ideal ones. Where a result implies a part you have to buy, the tools give you the nearest E-series value, the substitution error, and the power the part must survive.
• Everything runs locally. All the maths happens in JavaScript in your browser. Nothing you type is transmitted, logged or stored. The tools keep working offline once a page has loaded.
• Fast on bad connections. No frameworks, no build-time bloat, no client-side routing. A workshop with two bars of signal is the design target.
• Explanations alongside the answer. Every tool includes the formula it uses and the practical caveats, because knowing why 150 Ω is the answer is more durable than knowing that it is.

How it is funded

OhmCalc is free and supported by advertising. Ads are placed to stay out of the way of the calculator itself — nothing overlays the tools, nothing moves once the page has settled, and there are no interstitials. What that means for cookies and data is set out in the privacy policy.

Accuracy and limitations

The formulas used are standard and are stated on each page so you can check them. That said, these are engineering aids, not a substitute for a datasheet, a standard, or your own judgement. Component tolerances, temperature effects, derating curves and safety margins are your responsibility. Anything that could injure someone or start a fire deserves a second calculation and a look at the manufacturer's documentation. See the terms of use.

Corrections

If a calculator gives a result you believe is wrong, or an explanation glosses over something that matters, please get in touch. Corrections to the maths take priority over everything else.