A four-band resistor reads as digit, digit, multiplier, tolerance: yellow-violet-red-gold is 4, then 7, times 100, so 4.7 kΩ at ±5 per cent — anywhere between 4.465 and 4.935 kΩ. Five bands use three digits instead of two, and a sixth band adds a temperature coefficient. The code exists because a resistor is too small to print a number on legibly, and it survives because it can be read from any angle.
The genuine difficulty is not the colours. It is working out which end to start from.
What do the colours mean?
One scale for digits and multipliers, a separate one for tolerance.
| Colour | Digit | Multiplier |
|---|---|---|
| Black | 0 | ×1 |
| Brown | 1 | ×10 |
| Red | 2 | ×100 |
| Orange | 3 | ×1,000 |
| Yellow | 4 | ×10,000 |
| Green | 5 | ×100,000 |
| Blue | 6 | ×1,000,000 |
| Violet | 7 | ×10,000,000 |
| Grey | 8 | — |
| White | 9 | — |
| Gold | — | ×0.1 |
| Silver | — | ×0.01 |
Gold and silver as a multiplier give sub-ohm values, which is why a gold third band means 0.1 rather than a tolerance. As a tolerance band, gold is ±5 per cent, silver ±10, brown ±1, red ±2.
Which end do you start from?
The end with the tolerance band on it goes last, and the tolerance band is usually separated by a wider gap. Gold and silver are unambiguous because they never appear as digits — if you can see one, that is the far end.
The awkward case is a five-band part with a brown tolerance band, because brown is also a digit. There the gap is the only clue, and if the gap is not obvious the reliable answer is a meter.
A four-band resistor with no visible fourth band is ±20 per cent, an old and now rare specification. In practice a missing band is more often a band you cannot see because the body colour is close to it.
Why do five and six bands exist?
Because two digits are not enough for a precision series. The E12 and E24 series that make up ordinary 5 per cent and 2 per cent stock are all two-digit values, from 10 through 82 — but the E48 and E96 series that a 1 per cent design reaches for contain values like 4.99 kΩ, 2.21 kΩ and 1.07 kΩ, which need three.
| Bands | Reads as | Typical tolerance |
|---|---|---|
| 4 | 2 digits, multiplier, tolerance | ±5% or ±10% |
| 5 | 3 digits, multiplier, tolerance | ±1% or ±2% |
| 6 | 3 digits, multiplier, tolerance, tempco | ±1% or tighter |
Brown-black-black-brown-brown is 1, 0, 0 times 10, so 1 kΩ at ±1 per cent — the same nominal value as a four-band part and guaranteed five times tighter.
What does the sixth band do?
It gives drift in parts per million per degree Celsius: brown is 100 ppm, red 50, orange 15, blue 10. A 10 kΩ part at 50 ppm shifts 5 Ω over a ten-degree change.
That matters more often than people expect, because in a precision circuit temperature drift can dwarf the initial tolerance. A 0.1 per cent resistor with a 100 ppm coefficient drifts by 0.1 per cent over ten degrees, doubling its error before anything else has happened.
It is also why a matched pair can beat a low-ppm single part in a divider. If both resistors drift together the ratio holds, and the ratio is what a divider actually depends on.
Not every value can be encoded, and that is a feature. The code carries two or three significant digits and a power of ten, so 4.7 kΩ and 47 kΩ are expressible and 4,712 Ω is not. Any value outside the standard series has to be built from a pair or specified as a precision part with the number printed on it.
Is it easier to go the other way?
Usually, when you are picking a part out of a tray rather than identifying one in hand. Knowing that 220 Ω should be red-red-brown makes an incorrectly stuffed board obvious at a glance, without a meter.
It is also the fastest check on a design. If a value cannot be expressed in the band count you are using, it is not a standard value — and a non-standard value in a schematic is usually a sign that the tolerance stack has not been thought about.
Questions people ask
What is yellow-violet-red-gold? 4.7 kΩ at ±5 per cent. It is probably the single most common resistor in existence.
Why do brown and red look the same? Under warm light they genuinely do, and orange joins them on an aged body. Daylight, a phone torch or a meter are the three fixes in ascending order of reliability.
How do I write 4k7 as a number? 4,700 ohms. The letter takes the place of the decimal point precisely so it cannot be lost in a photocopy or a bad print.
Are four-band resistors always 5 per cent? Usually, sometimes 10, and occasionally 2. The fourth band states it, which is why it is there.
Why is there sometimes a wider gap before the last band? Because the manufacturer is telling you which end is which. It is the only orientation clue on a part that is otherwise symmetrical, and it is worth looking for before guessing.
Find the tolerance band, read from the other end, and count the digits. The resistor colour code calculator decodes any of the three formats, the 4 band, 5 band and 6 band pages start from the count you are looking at, and value to colour code runs it in reverse for picking parts.