Electronics is written in code. Here is how to read it.
Coloured bands on a resistor, three digits on a capacitor, a zigzag on a schematic: each one is a compact code, and none of them is explained on the part itself.
This page decodes the ones a beginner meets first. The books take it from there.
01
Resistor colour bands
The first bands are digits. The last ones are the multiplier and the tolerance.
A through-hole resistor carries its value as coloured bands. Read from the end where the bands sit closer together. On a four-band resistor the first two bands are digits, the third is the multiplier and the fourth is the tolerance.
Digits: black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8, white 9.
Multiplier: the same colours count the zeros to add, so red means two zeros. Gold multiplies by 0.1 and silver by 0.01.
Tolerance: brown is 1 percent, red 2 percent, gold 5 percent and silver 10 percent.
Example: yellow, violet, red, gold is 4, 7, then two zeros: 4,700 ohms, or 4.7 kilohms, within 5 percent.
CHECKED OCTOBER 2026 Resistors: Decoding Resistor Markings SparkFun Electronics
Colour table for the digits 0 to 9, the multiplier band and the tolerance colours, with worked examples.
2016, AMENDED 2019 IEC 60062: Marking codes for resistors and capacitors ANSI Webstore
The international standard behind the colour code and the letter and digit codes printed on resistors and capacitors. The link is the store listing; the full text is a paid document.
02
Capacitor markings
Three digits, counted in picofarads.
Small ceramic capacitors are usually marked with three digits. The first two are the value and the third is the number of zeros to add, with the result in picofarads.
Example: 104 is 10 followed by four zeros: 100,000 picofarads, which is 100 nanofarads or 0.1 microfarads. 472 is 4,700 picofarads, or 4.7 nanofarads.
A letter after the digits gives the tolerance: J is 5 percent, K is 10 percent and M is 20 percent.
Electrolytic capacitors print the value and the voltage rating in full, and mark the negative lead with a stripe. Fit one backwards and it can fail, so check the stripe before you apply power.
CHECKED OCTOBER 2026 Capacitor Kit Identification Guide SparkFun Electronics
Explains the three-digit code, reading 104 as 100,000 picofarads, and notes that the stripe on an electrolytic capacitor usually marks the negative lead.
03
Schematic symbols
A schematic shows what connects to what, not where the parts sit.
A schematic is a map of connections. Lines are wires, and a dot where lines meet means they are joined. Lines that cross without a dot are not connected.
A resistor is drawn as a zigzag or a plain rectangle. A capacitor is two parallel plates. A diode is a triangle pointing at a bar, and conventional current flows in the direction the triangle points. An LED is a diode with two small arrows leaving it. The ground symbol marks the common point that voltages are measured from.
Parts are labelled with a letter and a number: R for resistors, C for capacitors, D for diodes, Q for transistors and U or IC for chips.
CHECKED OCTOBER 2026 How to Read a Schematic SparkFun Electronics
Symbols for resistors, capacitors, diodes and LEDs, how junction dots differ from crossing wires, and the table of name prefixes: R, C, D, Q and U.
04
Voltage, current and resistance
One formula sizes most of the resistors you will ever need.
Voltage equals current multiplied by resistance: V = I x R. Rearranged, R = V / I, which is the form you use to choose a resistor.
Example: an LED that drops about 2 volts and wants 10 milliamps, run from a 9 volt battery. The resistor has to drop the remaining 7 volts at 0.01 amps, so R = 7 / 0.01 = 700 ohms. Use the next common value up, such as 820 ohms, or 1 kilohm for a slightly dimmer LED.
Power matters too: P = V x I. Here the resistor dissipates 7 x 0.01 = 0.07 watts, well inside the rating of an ordinary quarter-watt part.
CHECKED OCTOBER 2026 Voltage, Current, Resistance, and Ohm's Law SparkFun Electronics
States V = I x R and works through choosing a current-limiting resistor for an LED on a 9 volt battery.
Where the books come in
These four codes get you through a first schematic. Getting Started in Electronics takes it from there: what each component does, how semiconductors and integrated circuits work, and 100 circuits to build and test.
See the book