Formula
A 4-band code is two digits, a multiplier, and a tolerance. A 5-band code adds a third digit before the multiplier. A 6-band code adds a temperature coefficient in ppm/°C. Gold as a multiplier is 0.1 and silver is 0.01. Gold as a tolerance, which is the last band of a 4-band code, is ±5%. The position decides which meaning applies.
4-band: (10 D1 + D2) × multiplier
5-band: (100 D1 + 10 D2 + D3) × multiplier
Going the other way, the value is rounded to two significant figures for 4-band and three for 5- and 6-band, then split into a digit and a power of ten that the multiplier colors can name. E12, E24, and E96 membership uses the IEC 60063 preferred numbers. A value is counted as a member when it matches a preferred number within 0.2%.
Worked examples
Red, violet, orange, gold. 2, 7, ×1,000, ±5% = 27 kΩ. In E12 and E24. Not in E96.
Brown, black, black, red, brown. 1, 0, 0, ×100, ±1% = 10 kΩ. In E12, E24, and E96.
27 kΩ asked back as a 4-band, 5% code. The same four colors: red, violet, orange, gold.
Reference
Digits, black through white, are 0 through 9. Tolerances on this page: gray 0.05%, violet 0.1%, blue 0.25%, green 0.5%, brown 1%, red 2%, gold 5%, silver 10%. Tempco colors: brown 100, red 50, orange 15, yellow 25, blue 10, violet 5 ppm/°C.
Questions
What is red, violet, orange, gold?
27 kΩ, ±5%. Red is 2, violet is 7, orange multiplies by 1,000, and gold is the 5% tolerance. 27 is in E12 and E24. It is not an E96 value.
How is a 5-band code different?
Three digits, then the multiplier, then the tolerance. Brown, black, black, red, brown is 100 × 100 = 10 kΩ, ±1%. A sixth band is the temperature coefficient.
Why is the color written out?
The swatch is a picture. The name and the digit are the value. A reader who cannot use the color still has the band.
Sources
- IEC 60063 preferred-number series E12, E24, and E96.
- Resistor color marking: two or three significant figures, a multiplier, a tolerance, and an optional temperature coefficient.