Bench and circuit-design calculators — Ohm’s law, component codes, LEDs, filters and timers.
The calculators this site started with. They are a neighbouring subject rather than part of installation work, and they are kept here together rather than mixed into the wiring calculators.
Useful, well tested, and honestly not what the site is trying to be known for.
The relationship everything else rests on.
Including the loading effect that makes dividers unsuitable as supplies.
Rounded up to a standard value, because rounding down overdrives the LED.
Colour bands, and the capacitor codes that are not what they look like.
104 is 100 nF, not 104 of anything.
Cutoff, time constant and the response plotted live.
Frequency, duty cycle and the traps in the datasheet.
Where the naive mAh ÷ mA answer goes wrong.
IPC-2221 and IPC-2152, internal and external layers.
Solve for voltage, current, resistance or power. Get all four values at once, plus the resistor wattage you actually need.
R1R2Calculate output voltage, ratio, current and output impedance — with the loading effect built in, not hidden on another page.
4-6Decode 4, 5 and 6-band resistors, or enter a value to see its bands. Tolerance range and temperature coefficient included.
104Decode ceramic capacitor markings — 104 is 100 nF, not 104 of anything — or work backwards from a value to the printed code.
LEDSize the current-limiting resistor for any LED. Rounds up to the nearest E24 value, because rounding down overdrives the LED.
fcCutoff frequency, time constant and rise time for a single-pole RC low-pass or high-pass, with the gain and phase at any test frequency plotted on a live Bode chart.
555Frequency, period, duty cycle and pulse width for the NE555 from R1, R2 and C — with the duty-cycle trap and the pin 7 current limits called out.
mAhHow long a load really runs from a given cell — duty cycle, regulator topology and self-discharge included, which is exactly where the naive mAh ÷ mA answer goes wrong.
IPCMinimum trace width for a given current and temperature rise, to IPC-2221B — in mils and mm, with copper area, resistance, voltage drop and final conductor temperature.
9 calculators in this category. Every one is free to use on ElectroCalculators, with no account required, and every result cites the standard it came from.