๐ Electronics
Resistor decoders, LED calculators, capacitor tools and more for electronics hobbyists
Decode 4-band and 5-band resistor color codes instantly. Free visual resistor calculator.
Open tool โCalculate the resistor needed for an LED circuit. Enter supply voltage, LED forward voltage and current.
Open tool โDecode 3-digit ceramic capacitor codes (e.g. 104 = 100nF). Instant conversion to pF, nF, ยตF.
Open tool โCalculate output voltage from a resistive voltage divider. Enter Vin, R1, R2.
Open tool โCalculate frequency, duty cycle, and timing for 555 timer circuits in astable and monostable modes.
Open tool โCalculate minimum PCB copper trace width for a given current, using IPC-2221 standards.
Open tool โAWG wire gauge reference table with diameter, area, resistance, and max current ratings.
Open tool โCalculate the time constant, charge time, and discharge curves for RC circuits.
Open tool โDecode 4-band inductor color codes to inductance in ยตH and mH.
Open tool โCalculate voltage, current, resistance, or power from any two known values.
Open tool โDecode 3-digit, 4-digit, and EIA-96 SMD resistor codes to resistance values.
Open tool โComponent maths for people with a breadboard in front of them. These tools cover the calculations you hit repeatedly while building a circuit: what resistor a part needs, what a colour band or SMD marking means, how wide a trace has to be, and how long an RC network takes to settle.
Everything is worked in the open. Each tool shows the formula it used and the numbers it put into it, so you can check the result against your own working rather than trusting a black box โ which matters when the consequence of a wrong answer is a dead component.
Which tool do I want?
| If youโฆ | Use |
|---|---|
| You have a resistor in hand and need its value | Resistor Color Decoder |
| The part is surface-mount with a 3 or 4 character code | SMD Resistor Code Decoder |
| You are driving an LED and need the series resistor | LED Resistor Calculator |
| You need to drop a voltage down to a reference level | Voltage Divider Calculator |
| You are sizing wire for a current, or worried about heat | Wire Gauge (AWG) Reference |
| You are laying out a board and need copper width | PCB Trace Width Calculator |
| You are building a timer or oscillator | 555 Timer Calculator |
| You need a time constant for filtering or debouncing | RC Time Constant Calculator |
Tolerance is the thing beginners forget
Every calculation here produces an exact number, and no component you can buy is exact. A resistor sold as 220 ฮฉ with a gold band is guaranteed only to sit within 5% of that โ anywhere from 209 to 231 ฮฉ. Stack a few 5% parts in one divider and the output can drift further than the reading you were trying to achieve.
This matters most where a result feeds a threshold. A divider setting a comparator trip point, a timing network deciding a pulse width, a current limit sitting just under a part's maximum โ in those places, work out what the answer becomes at the tolerance extremes, not just at the nominal value. Where it matters, buy 1% parts; they cost almost nothing more.
The same applies to the standard value the tools round to. E24 gives you 24 values per decade, so the nearest stocked resistor to a calculated 237 ฮฉ is 240 ฮฉ. That is usually fine, and the tools tell you both numbers so you can decide.