Electronics is the category where the definitions do most of the work. An ohm is defined so that one volt across it drives one ampere, and a watt so that one volt at one ampere delivers a joule every second — so the arithmetic behind Ohm's law, a divider, an LED resistor, an RC time constant and a 555 period is those two statements rearranged, not an empirical rule with exceptions. Two things here are not like that. The width of a copper track is an empirical curve fitted to measurements in the 1950s, and it is quoted as such. A signal level in dBm becomes a voltage only once you name an impedance, so that impedance is a field rather than a hidden constant. What the formulas will not tell you is where they stop applying: a diode is not a resistor, capacitors combine the opposite way round to resistors, and a part rated exactly at the power it dissipates is a part running too hot. Each tool says where its own limits are.
Tools in this category
Ohm's law calculator
Give any two of voltage, current, resistance and power, and this works out the other two — including the power the resistor has to dissipate.
RC time constant calculator
Work out the time constant of a resistor and capacitor, the −3 dB corner it puts on a low-pass filter, and how long a step takes to settle.
555 timer calculator
Frequency, high and low times and duty cycle of a 555 running free, or the pulse width of a single shot, from the two resistors and the capacitor.
Resistor value to colour code
Give a resistance and a tolerance and get the bands to paint on it, in order, for a 4, 5 or 6-band code — the reverse of reading a resistor.
Resistor colour code calculator
Read the bands on a resistor and get its value, its tolerance and the range the real part is allowed to fall in — for 4, 5 and 6-band codes.
Voltage divider calculator
Work out what two resistors in series do to a supply voltage, how much current they draw doing it, and how much each of them turns into heat.
LED resistor calculator
Work out the series resistor an LED needs on a given supply, rounded up to a value you can actually buy, with the power it has to dissipate.
Resistors and capacitors in series and parallel
Combine any number of resistors or capacitors in series or in parallel, and see the same parts wired the other way round beside the answer.
PCB trace width calculator
Size a printed circuit track for the current it has to carry and the temperature rise you will accept, in millimetres and in mils.
dBm, watts and volts converter
Convert between dBm, watts and volts — rms, peak and peak to peak — against the reference impedance you pick, whether that is 50 Ω, 600 Ω or your own.
Suggest a tool
Tell us what is missing and where its numbers should come from.
What should it convert, calculate or generate, and where would the authoritative numbers come from? A link to the standard or publication that defines them is the most useful thing you can send.
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How these tools are built
Every tool in this category runs entirely in your browser: there is no upload, no account and no request to a server once the page has loaded. The numbers behind them are transcribed from the organisation that defines them — NIST for units, the W3C for web formats, the WHO for health measures — and each page names its source next to the formula. A tool whose reference values stop reproducing fails the build and does not ship, which is the whole reason the catalogue grows slowly.