Three digits (473), four digits (4702), an R for the decimal point (4R7), or an EIA-96 code (01C).
Plain ohms, or 4k7, 2.2M, 470R.
The 4-band code (IEC 60062): two significant figures and a power of ten. 5- and 6-band parts add a third digit and a temperature coefficient.
Stock values are logarithmic: E12 steps by ×1.21 (101/12), E24 doubles the density for ±5%, E96 has 96 per decade for ±1%.
A ±10% part at 47 covers 42.3–51.7; the next, 56, covers 50.4–61.6. The ranges meet, so every value is within tolerance of some stocked part.
A single black band is a deliberate wire link in a resistor body: a jumper, or a link you can cut to change an option.
Twelve equal steps span a decade (101/12 = 1.212), so 4.7 kΩ, 47 kΩ and 470 kΩ all exist and 5 kΩ does not. E24 adds 11, 13, 16, 20, 24, 30, 36, 43, 51, 62, 75 and 91. Asking for a value not in the series is usually pointless rather than unlucky: the nearest stocked part, with its tolerance, very often contains the number you wanted. If your circuit cares about 2%, E24 cannot express it and E96 can.
The classic misread: brown (1) against red (2), red against orange (3), on a dark body, under warm lighting or on an aged part, and getting it wrong is a factor-of-ten error. Faded or heat-darkened parts drift the wrong way too. Read the part on a white background in daylight, and sanity-check the answer against what the circuit ought to need.
An in-circuit reading is the resistor in parallel with every other path around it, so it comes out lower than the true value, sometimes far lower. Lift one leg first, and make sure the board is powered down and any capacitors have discharged.
Work out V²/R and pick a part rated for at least twice it. 5 V across 220 Ω is 0.114 W: arithmetic says an eighth-watt part, practice says a quarter. Ratings are measured in still air at 25 °C with the part on its own; in an enclosure, beside other parts, on a warm board, the real limit is lower. The colour code says nothing about power rating: that comes from the physical size of the part.
The tolerance band (gold or silver) is usually set slightly apart toward one end: start from the other end. When encoding, a value that is not exactly two digits times a power of ten is rounded to the nearest representable one.
The tolerance band (gold/silver) is usually set slightly apart toward one end — start from the other end.
Not every ohm value maps to exact 2-digit × 10ⁿ bands. Encode mode rounds to the nearest representable 4-band value.
The IEC 60062 colour code in 4-, 5- and 6-band forms: 4-band parts read two significant digits, 5- and 6-band parts three, and the 6-band adds a temperature-coefficient band. It assumes the bands are read from the end furthest from the tolerance band, and that the colours are true — both assumptions fail often enough in practice to be worth checking. Not covered: the obsolete body-tip-dot scheme and surface-mount numeric codes. The colour code says nothing at all about power rating — that comes from the physical size of the part.
Releases in which this page changed, newest last. Derived from the archived copy of every release, not from notes written afterwards — so it reflects what actually shipped. Site-wide passes are left out; they are in the full changelog.