Resistor Value → Color Code
Turns a resistance you have calculated into a part you can buy and find in a drawer. Enter the target value and pick a preferred series. The page gives the nearest standard value in that series, and the color bands that mark it. Use it when a design formula gives an odd value, or when you need to know what to look for in a parts bin.
How it works
R = c·10m
The preferred series of IEC 60063 [1] space standard values evenly on a log scale. E6 has 6 values per decade, E12 has 12, and so on up to E192. Each series goes with a tolerance: E6 ±20 %, E12 ±10 %, E24 ±5 %, E48 ±2 %, E96 ±1 % and E192 ±0.5 %. c is the series value as its significant digits: two digits for E6 to E24 (10, 12, 15 … 91) and three for E48 and up (100, 102, 105 …). m is the power of ten that sets the decade. The page picks the series value whose ratio to your target is closest to 1, which is nearest on a log scale. It may cross into the next decade, so 9.8 kΩ in E12 gives 10 kΩ. The value it returns is exact: a standard value, not a rounded result.
The color code follows IEC 60062 [2]. A two-digit value takes a 4-band code and a three-digit value a 5-band code. The digit bands give c, the multiplier band gives m (gold −1, silver −2), and the last band gives the tolerance of the series.
Limits and common mistakes
- The nearest value can be up to half a step off: about 10 % in E12, 5 % in E24 and 1.2 % in E96. If that matters, choose a finer series or use two resistors in series.
- A part from a finer series is often stocked only in that series’ tolerance. A 15.8 kΩ resistor is a 1 % part, not a 5 % one.
- The color code covers about 0.1 Ω to 99 GΩ with two digits and 1 Ω to 999 GΩ with three. Outside that range the page returns an error.
- Surface-mount parts use printed number codes instead of colors.
Worked example
A first-order RC low-pass filter needs a 1 kHz corner with a 10 nF capacitor. R = 1/(2π·1000·10 nF) works out to 15,915 Ω. Which 1 % resistor should be fitted?
- Enter Target resistance 15915 Ω.
- Choose Preferred series (IEC 60063) E96 (±1 %) and press Solve. The Solution shows:
Nearest standard value: 15.8 kΩ
Color code: 5-band (three significant digits)
Band 1: Brown
Band 2: Green
Band 3: Gray
Multiplier band: Red
Tolerance band: Brown (±1%)
Check: the E96 values around the target are 15.8 and 16.2 kΩ. 15.915/15.8 is 1.0073, and 16.2/15.915 is 1.0179, so 15.8 kΩ is nearer. The bands read 1, 5, 8 × 102 = 15,800 Ω. The corner moves to 1007 Hz, well inside the tolerance of the capacitor.
