Resistor colour codes
Different values of resistor can look very similar. On the other hand, 2 resistors that are the same value can look quite different. Even when limiting to the through-hole style used for the ARDX kit. Ignoring a lot of details that are not important here, a thru-hole, axial lead, resistor is a cylindrical device, often with rounded ends, or dumb-bell shaped, with a wire coming from each end. The main body of the resistor is painted, or coated, to protect the resistor itself, then bands of colour are painted over top. The colour of the body can vary, but does not have any relation to the value of the resistor.
Only the cylindrical bands need to be considered to determine the value.
| Colour | Digit1 | Digit2 | Digit3ǂ | Multiplier | Tolerance | TemperatureCoefficient | FailureRate |
|---|---|---|---|---|---|---|---|
 None |
±20% (M) | ||||||
 Silver |
x0.01 | ±10% (K) | |||||
 Gold |
x0.1 | ±2% (J) | |||||
 Black |
0 | 0 | 0 | x100 | |||
 Brown |
1 | 1 | 1 | x101 | ±1% (F) | 100 ppm/K | 1% |
 Red |
2 | 2 | 2 | x102 | ±2% (G) | 50 ppm/K | 0.1% |
 Orange |
3 | 3 | 3 | x103 | 15 ppm/K | 0.01% | |
 Yellow |
4 | 4 | 4 | x104 | 25 ppm/K | 0.001% | |
 Green |
5 | 5 | 5 | x105 | ±0.5% (D) | ||
 Blue |
6 | 6 | 6 | x106 | ±0.25% (C) | ||
 Violet |
7 | 7 | 7 | x107 | ±0.1% (B) | ||
 Grey |
8 | 8 | 8 | x108 | ±0.05% (A) | ||
 White |
9 | 9 | 9 | x109 |
ǂ 3rd digit - only for 5 or 6 band resistors
- A 3 band resistor will use 2 digits, a multiplier, and none for the tolerance
- A 4 band resistor will use 2 digits, a multiplier, and a tolerance
- A 5 band resistor will use 3 digits, a multiplier, and a tolerance
- A 6 band resistor will use 3 digits, a multiplier, a tolerance, and a temperature coefficient
Example: A 1.2KΩ (1200Ω) resistor could be:
- 3 bands: brown-red-red = 1 2 x102 = 12 * 100, ±20%
- 4 bands: brown-red-red-gold = 1 2 x102, ±5% = 12 * 100, ±5%
- 5 bands: brown-red-black-brown-green = 1 2 0 x101, ±0.5% = 120 * 10, ±0.5%
The tolerance band of 4 band resistors is often gold (±5%) or silver (±10%). Gold and silver are not valid digit band colours, so finding that on the end shows which way to read the bands.
If there are no gold or silver bands, it can be more difficult to determine which direction to read them. Some manufactures group the colour bands, leaving a slightly larger gap between the multiplier and tolerance. If there is a gap, the longer group includes the starting digits.
For 4 and 5 band resistors, the final band is the tolerance. Only some of the colours are used for tolerance, so if the end band is orange, yellow, or white, it is the first digit, not the tolerance.
For 6 band resistors, the temperature coefficient is the final band, which can only be brown, red, orange, or yellow. The second last band is the tolerance, which has the limitations shown above for 5 band resistors.
There are preferred values that fit standard series of resistor values. Sometimes reading the colour bands gives a technically valid value either direction. However, some values are much less likely than others. The values (digits colour bands only) from those series are preferred, standard values. They are much more common, produced in higher volumes, and therefore tend to be cheaper than other values. Custom circuits may need values not in the standard ranges, but unless there is a special need, it is very likely that the available resistors will be in one of 'E' series. For example, a 5 band, 1KΩ, 0.5% tolerance (E192 Series) resistor is brown-black-black-brown-green (100x101, 0.5%). Reading backwards, green-brown-black-black-brown would be 510x100 (510Ω) 1%. 510 does not exist in the E96 (1%) series.
Higher tolerance resistors tend to be cheaper, so the lower numbered 'E' series tend to be more common (although the E3, E6, and even E12 series are not seen much anymore). For example, a 5 band, 560Ω, 2% tolerance (E48 series) resistor is blue-green-black-black-red (560x100 2%). Reading backwards, red-black-black-green-blue would be 200x105 (20MΩ) 0.25%. A 0.25% tolerance is unlikely to be found in a standard resistor package used for the ARDX kits.
Sometimes there is no definitive way of directly telling from the colours. A 5 band, 1K, 2% tolerance (E48 series) resistor is brown-black-black-brown-red (100x101 2%). Reading backwards, red-brown-black-black-brown would be 210x100 (210Ω) 1%. A standard E96 series resistor value. Time to get out the ohm meter.