Resistors are among the smallest components in electronics, and their values are printed on them not as numbers but as coloured bands. The colour code exists because a tiny cylindrical component has no flat surface for legible text, and because a code readable from any angle suits automated assembly. Learning the code takes an afternoon and pays off for years, because it lets you identify a resistor from a parts bin, verify a circuit without a meter, and catch a wrong component before it is soldered in. The system is logical once the table is memorised, and a few worked examples will fix it in place.
The code assigns a digit to each colour: black is 0, brown is 1, red is 2, orange is 3, yellow is 4, green is 5, blue is 6, violet is 7, grey is 8, and white is 9. Several mnemonics exist for this order; the traditional one runs "black, brown, red, orange, yellow, green, blue, violet, grey, white", and many learners invent their own sentence from the initials. Gold and silver do not appear as digits; they appear as multiplier or tolerance bands, which is a useful distinction to remember. In a standard four-band resistor, the first two bands are the significant digits, the third band is the multiplier, meaning the power of ten by which the two digits are multiplied, and the fourth band, separated by a gap from the others, is the tolerance, meaning how far the actual resistance may deviate from the stated value. Gold as a tolerance band means plus or minus 5 percent, silver means plus or minus 10 percent, and brown means plus or minus 1 percent.
Consider a worked example. A resistor carries the bands yellow, violet, red, gold. Yellow is 4 and violet is 7, so the significant digits are 47. Red as a multiplier means 10², which is 100. The resistance is therefore 47 × 100, which is 4,700 ohms, or 4.7 kilohms. Gold as the tolerance means plus or minus 5 percent, so the actual resistance may lie between 4,700 × 0.95, which is 4,465 ohms, and 4,700 × 1.05, which is 4,935 ohms. A meter reading anywhere in that range is consistent with the code, and a reading far outside it suggests a faulty or misread component. A second example: brown, black, orange, gold. Brown is 1 and black is 0, giving 10. Orange as a multiplier means 10³, which is 1,000. The resistance is 10 × 1,000, which is 10,000 ohms, or 10 kilohms, with a tolerance of plus or minus 5 percent, giving a range of 9,500 to 10,500 ohms. A third example, red, red, brown, gold: red is 2 and red is 2, giving 22, and brown as a multiplier means 10¹, which is 10, so the resistance is 22 × 10, which is 220 ohms, again plus or minus 5 percent.
Five-band resistors add a third significant digit for precision, and the structure shifts accordingly: the first three bands are digits, the fourth is the multiplier, and the fifth is the tolerance. Consider brown, black, black, red, brown. The digits are 1, 0, and 0, giving 100. Red as a multiplier means 100, so the resistance is 100 × 100, which is 10,000 ohms, or 10 kilohms. Brown as a tolerance means plus or minus 1 percent, giving a range of 9,900 to 10,100 ohms. The extra digit and the tighter tolerance are the point of the five-band system: precision circuits need to distinguish 10.0 kilohms from 10.2 kilohms, which a two-digit code cannot express. Six-band resistors add a sixth band for the temperature coefficient, which describes how the resistance drifts with temperature, measured in parts per million per degree; this matters in precision and high-temperature applications but is rarely needed for general work, and the first five bands read exactly as above.
Reading direction is the most common source of errors. The tolerance band is usually separated from the other bands by a larger gap, and reading should start from the end opposite the tolerance band. When the gap is unclear, several clues help: gold and silver bands are always tolerance bands, never digits, so a resistor with a gold band at one end is read from the other end. Brown as a tolerance band, for plus or minus 1 percent, is usually the last band of a five-band resistor, and the first band is rarely black, since a leading zero would be pointless, though it does occur. If a reading gives a value that does not match a standard series, such as the E12 or E24 preferred values, the resistor has probably been read backwards. For example, reading the yellow-violet-red resistor backwards as red-violet-yellow would give 27 × 10,000, which is 270,000 ohms, a value that is not in the same standard series position and should immediately arouse suspicion. When in doubt, measure with a multimeter: the meter is the final authority, and the code is a quick check, not a replacement for measurement.
The standard value series deserve a brief explanation, because they explain why the decoded values look the way they do. Resistors are manufactured in preferred series with values spaced roughly logarithmically, so that the tolerance bands of adjacent values just overlap. The E12 series, for 10 percent tolerance, has twelve values per decade: 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, and 82, each multiplied by powers of ten. The E24 series, for 5 percent tolerance, adds intermediate values, and the E96 series, for 1 percent tolerance, has ninety-six values per decade. That is why 4.7 kilohms and 10 kilohms appear constantly while 4.6 kilohms does not: the former are standard values, the latter is not, except in the tightest tolerance series. Designing with standard values avoids custom parts, and recognising them helps confirm a reading.
A practical workflow for identifying an unknown resistor runs as follows. Hold it so the tolerance band, gold or silver, is on the right, with the other bands to its left. Read the digit bands from left to right, look up the multiplier, and compute the value. Check that the value is a standard series value for the stated tolerance. If the circuit is sensitive, verify with a multimeter, measuring with the resistor out of circuit where possible, since parallel paths in a powered or populated board distort in-circuit readings. Record the value and tolerance alongside the component in your notes, because a resistor identified once and then mixed back into a bin will need identifying again. And when stocking parts, keep the common values, such as 220 ohms, 1 kilohm, 4.7 kilohms, and 10 kilohms, in labelled compartments; organisation beats decoding speed for day-to-day work.
This guide is educational guidance for reading resistor markings. It does not replace component datasheets or measurement, and it does not cover mains-voltage or safety-critical design. Electrical work should follow local codes, and designs that carry significant power or that affect safety should be checked by a qualified engineer or electrician.
Try it next: use the Resistor Color Code Calculator to decode a resistor, then check series values with the Voltage Divider Calculator and the Scientific Calculator. For background reading, see LED Series Resistor Sizing.