Resistor colour code, reading and lookup
4 bands: digit, digit, multiplier, tolerance
The colour code both ways round, as at the bench: read the bands of a resistor to its value and tolerance interval, or start from a wanted value and get the bands to look for in the drawer. The requested value is projected onto the normalised series of its tolerance (E24 for 5%, E96 for 1%), because 5,000 Ω is not manufactured: the honest answer is 5.1 kΩ, with the gap shown. The tool also flags the backwards reading when it is plausible, the real source of mistakes, and the off-series values that betray it.
4.7 kΩ
- Tolerance
- ± 5 %
- Guaranteed real value
- between 4.465 kΩ and 4.935 kΩ
This resistor is 4.7 kΩ, within 5%.
Reading direction: the tolerance band (gold, silver, or a band set apart from the group) goes on the right. Gold and silver can never open a code, which is the safest way to orient yourself.
Commercial values follow the IEC 60063 normalised series: E24 for 5% (24 values per decade), E96 for 1% (96 values). These series are geometric: each value sits about 10% or 2.4% above the previous one, so that tolerance intervals just overlap.
Scientific dossier
What the tool computes, what it assumes, where it stops being valid, and where its data comes from.
Method & formulas4 bands: digit, digit, multiplier, tolerance
4 bands: digit, digit, multiplier, tolerance
5 bands: digit, digit, digit, multiplier, tolerance
value = digits × 10^multiplier
gold = ±5%, brown = ±1%, silver = ±10%
Each colour carries a digit from 0 (black) to 9 (white); the second-to-last band is a power of ten, the last one the tolerance. Gold and silver carry no digit: they can only sit on the multiplier (dividing by 10 or 100) or the tolerance, and that is precisely what lets you orient the reading.
- Tolerance
- · the gap the manufacturer guarantees: a 1 kΩ at 5% really sits between 950 and 1,050 Ω.
- E24 series
- · 24 normalised values per decade (1.0, 1.1, 1.2… 9.1), those of 5% resistors.
- E96 series
- · 96 values per decade, three significant figures, those of the 1%.
- Decade
- · a factor of 10: the series repeat identically from 1 Ω to 10 Ω, 10 to 100, and so on.
Validity domainThe code covers through-hole resistors with 4 and 5 bands per IEC 60062, from 0.
The code covers through-hole resistors with 4 and 5 bands per IEC 60062, from 0.1 Ω to 9.99 GΩ. Six-band codes add a temperature coefficient, not handled here; surface-mount parts use numeric marking, not colours. The tolerance band goes on the right to read; when both reading directions each give a plausible value, the tool shows both and flags the ambiguity, the value outside the normalised series being almost always the backwards reading.
Reading the resultThe guaranteed interval matters more than the nominal value: a circuit that demands better than the tolerance of its parts will not work reproducibly.
The guaranteed interval matters more than the nominal value: a circuit that demands better than the tolerance of its parts will not work reproducibly. When the requested value does not exist in the series, the tool serves the closest one in relative terms, the series being geometric, and shows the gap: for an exact value, combine several resistors in series or parallel.