Resistor colour code and SMD decoder

Brown, black, red, gold reads 1 kΩ ±5 %, anywhere from 950 Ω to 1.05 kΩ. Under IEC 60062, brown is 1, black is 0 and a red third band is ×100. On an SMD chip, 103 is 10 × 10³, which is 10 kΩ, not 103 Ω. Two digits and a letter is EIA-96 instead: 68C is 49.9 kΩ.

Colour bands or SMD markings to a resistance, with tolerance range and the nearest preferred values.

Fig 1 — 4-band axial resistor: brown, black, red, gold.

Input mode

Band count

Digit band 1

Digit band 2

Multiplier band

Tolerance band

Resistance: 1.00 kΩ
Tolerance: ±5 %
Range: 950 Ω to 1.05 kΩ
Nearest E12: 1.00 kΩ (exact)
Nearest E24: 1.00 kΩ (exact)
SMD 3-digit: 102
SMD 4-digit: 1001

How this is calculated

Standard: IEC 60062 (marking codes) and IEC 60063 (E-series preferred numbers)

$R = \text{significant digits} \times 10^{\,\text{band}}$: Colour bands. The digit bands give the significant figures and the multiplier band gives the power of ten.
$R = \text{leading digits} \times 10^{\,\text{last digit}}$: SMD three- and four-digit codes.
$\text{4R7} = 4.7\ \Omega$: SMD R-notation, where the R stands in for the decimal point.
$\text{68C} = 49.9\ \text{k}\Omega$: EIA-96. The two digits index the E96 series — 68 selects the 68th value, 499 — and the letter gives the decade, C being ×100.

Assumptions

Four-band codes use two significant digits; five-band codes use three.
Nearest E-series value is chosen by smallest logarithmic distance.
EIA-96 letters R and Y both mean ×0.01, X and S ×0.1, B and H ×10.
A trailing R is read as a decimal point, so 10R is 10 Ω rather than an EIA-96 code.
Does not cover temperature-coefficient (sixth) bands.

What resistor markings encode

Two marking systems, both defined in IEC 60062 (Marking codes for resistors and capacitors): colour bands on leaded parts, and printed alphanumeric codes on chips. Both encode a small number of significant digits and a power-of-ten multiplier. The decoder turns either into ohms, then looks up the closest E12 and E24 values from IEC 60063.

Colour bands (IEC 60062 clause 3)

Digits are black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8, white 9. The multiplier band uses the same colours as 10^n, plus gold for ×0.1 and silver for ×0.01. Tolerance: brown 1 %, red 2 %, green 0.5 %, blue 0.25 %, violet 0.1 %, grey 0.05 %, gold 5 %, silver 10 %. No tolerance band on old parts meant 20 %.

4 bands:  d1 d2 × 10^m, tolerance
5 bands:  d1 d2 d3 × 10^m, tolerance
6 bands:  as 5 bands, plus temperature coefficient
          (brown 100, red 50, orange 15, yellow 25, blue 10, violet 5 ppm/K)

The tool covers 4 and 5 bands. A sixth tempco band does not change the value; drop it and read the remaining five.

SMD codes (IEC 60062 clause 4)

3-digit:  d1 d2 × 10^d3           473  = 47 × 10³ = 47 kΩ
4-digit:  d1 d2 d3 × 10^d4        4702 = 470 × 10² = 47 kΩ
R-code:   R is the decimal point   4R7  = 4.7 Ω    R22 = 0.22 Ω   10R = 10 Ω
EIA-96:   d1 d2 = E96 index, letter = multiplier
          Z ×0.001  Y/R ×0.01  X/S ×0.1  A ×1  B/H ×10  C ×100  D ×1k  E ×10k  F ×100k

3-digit is the 5 % (and older 1 %) convention. 4-digit is the 1 % convention on 0805 and larger. EIA-96 is what 1 % parts get when there is no room for four characters: 0603 and 0402. The 96 index values are exactly the E96 series, so 01 = 100, 02 = 102, ... 96 = 976, and the letter gives the decade. A code with an R anywhere in it is read as R-notation first, because "10R" on a real part means 10 Ω and almost never E96 index 10 scaled by 0.01.

Resistor colour code chart

One row per band colour, and what that colour means depending on which band it is sitting in. A colour is not one number: brown is the digit 1 as a significant band, a multiplier of ten as the third band, and ±1 % as the tolerance band. Dashes mark the positions a colour is never used in, which is why gold and silver can only ever be the last two bands.

Colour	Digit	Multiplier	Tolerance
Black	0	×1	—
Brown	1	×10	±1 %
Red	2	×100	±2 %
Orange	3	×1,000	—
Yellow	4	×10,000	—
Green	5	×100,000	±0.5 %
Blue	6	×1,000,000	±0.25 %
Violet	7	×10,000,000	±0.1 %
Grey	8	×100,000,000	±0.05 %
White	9	×1,000,000,000	—
Gold	—	×0.1	±5 %
Silver	—	×0.01	±10 %

Common values and their bands

The E12 values from 10 Ω to 1 MΩ, in the four-band ±5 % form, which is what a leaded resistor in a drawer almost always is. Every row is produced by running the decoder backwards, so these are the bands that decode to that resistance and not a transcription of somebody else's chart.

Resistance	Band 1	Band 2	Multiplier	Tolerance
10 Ω	Brown	Black	Black	Gold
12 Ω	Brown	Red	Black	Gold
15 Ω	Brown	Green	Black	Gold
18 Ω	Brown	Grey	Black	Gold
22 Ω	Red	Red	Black	Gold
27 Ω	Red	Violet	Black	Gold
33 Ω	Orange	Orange	Black	Gold
39 Ω	Orange	White	Black	Gold
47 Ω	Yellow	Violet	Black	Gold
56 Ω	Green	Blue	Black	Gold
68 Ω	Blue	Grey	Black	Gold
82 Ω	Grey	Red	Black	Gold
100 Ω	Brown	Black	Brown	Gold
120 Ω	Brown	Red	Brown	Gold
150 Ω	Brown	Green	Brown	Gold
180 Ω	Brown	Grey	Brown	Gold
220 Ω	Red	Red	Brown	Gold
270 Ω	Red	Violet	Brown	Gold
330 Ω	Orange	Orange	Brown	Gold
390 Ω	Orange	White	Brown	Gold
470 Ω	Yellow	Violet	Brown	Gold
560 Ω	Green	Blue	Brown	Gold
680 Ω	Blue	Grey	Brown	Gold
820 Ω	Grey	Red	Brown	Gold
1 kΩ	Brown	Black	Red	Gold
1.2 kΩ	Brown	Red	Red	Gold
1.5 kΩ	Brown	Green	Red	Gold
1.8 kΩ	Brown	Grey	Red	Gold
2.2 kΩ	Red	Red	Red	Gold
2.7 kΩ	Red	Violet	Red	Gold
3.3 kΩ	Orange	Orange	Red	Gold
3.9 kΩ	Orange	White	Red	Gold
4.7 kΩ	Yellow	Violet	Red	Gold
5.6 kΩ	Green	Blue	Red	Gold
6.8 kΩ	Blue	Grey	Red	Gold
8.2 kΩ	Grey	Red	Red	Gold
10 kΩ	Brown	Black	Orange	Gold
12 kΩ	Brown	Red	Orange	Gold
15 kΩ	Brown	Green	Orange	Gold
18 kΩ	Brown	Grey	Orange	Gold
22 kΩ	Red	Red	Orange	Gold
27 kΩ	Red	Violet	Orange	Gold
33 kΩ	Orange	Orange	Orange	Gold
39 kΩ	Orange	White	Orange	Gold
47 kΩ	Yellow	Violet	Orange	Gold
56 kΩ	Green	Blue	Orange	Gold
68 kΩ	Blue	Grey	Orange	Gold
82 kΩ	Grey	Red	Orange	Gold
100 kΩ	Brown	Black	Yellow	Gold
120 kΩ	Brown	Red	Yellow	Gold
150 kΩ	Brown	Green	Yellow	Gold
180 kΩ	Brown	Grey	Yellow	Gold
220 kΩ	Red	Red	Yellow	Gold
270 kΩ	Red	Violet	Yellow	Gold
330 kΩ	Orange	Orange	Yellow	Gold
390 kΩ	Orange	White	Yellow	Gold
470 kΩ	Yellow	Violet	Yellow	Gold
560 kΩ	Green	Blue	Yellow	Gold
680 kΩ	Blue	Grey	Yellow	Gold
820 kΩ	Grey	Red	Yellow	Gold

Worked example: four colour bands, and an EIA-96 code

Leaded part, four bands: yellow, violet, orange, gold.

yellow = 4, violet = 7          → 47
orange = ×10³                   → 47 000 Ω = 47 kΩ
gold   = ±5 %                   → 44.65 kΩ to 49.35 kΩ   (shown as 44.7 to 49.4 kΩ)

nearest E12 = 47 kΩ
nearest E24 = 47 kΩ

Same value as a chip, three ways. "473" gives 47 × 10³. "4702" gives 470 × 10². Both decode to 47 kΩ. Now the 1 % neighbour in EIA-96, marked "68C":

index 68 → E96 table entry 68 = 499
C        → ×100
value    = 499 × 100 = 49 900 Ω = 49.9 kΩ

E12 candidates around 49.9 k: 47 k, 56 k
  |ln(49.9/47)| = 0.060    |ln(56/49.9)| = 0.115   → 47 kΩ
E24 candidates: 47 k, 51 k
  |ln(49.9/47)| = 0.060    |ln(51/49.9)| = 0.022   → 51 kΩ

Entering 68C gives 49.9 kΩ, nearest E12 47 kΩ, nearest E24 51 kΩ. Note the E12 and E24 answers differ; the tool minimises log distance in each series independently, it does not assume E24 contains the E12 pick.

Where the marking stops telling you the value

Zero-ohm links. A single black band, or "0", "00", "000". The tool returns 0 Ω and skips the E-series rows, which have no meaning for a jumper.
Manufacturer-specific codes. Some vendors print a two-character or three-character code that is a catalogue lookup, not an IEC scheme. Panasonic, Yageo and Bourns all have variants. Capacitor and inductor markings use the same digit-multiplier idea in pF and nH, but the R-code means µH on an inductor and not ohms.
Faded parts. Red/orange and brown/violet are routinely confused on old bodies. Measure it when it matters.
Tolerance range only. The range row is the marked tolerance at delivery. It says nothing about drift, tempco (typically ±100 to ±200 ppm/K for thick film) or the resistance after soldering.

Common resistor code mistakes

Reading from the wrong end. The tolerance band is usually separated from the others by a wider gap and sits nearest one end. Gold and silver are never digit colours, so if the first band you read is one of those, turn the part around. Five-band parts with a brown tolerance band are genuinely ambiguous (brown is a valid digit); try both readings and pick the one that lands on an E96 value.
Counting bands wrong on a 5-band part. Reading a 5-band 1 % part as 4-band shifts the multiplier one band left. Brown, black, black, red, brown is 10 kΩ 1 %, not 100 Ω 2 %.
Treating the third SMD digit as a digit. "103" is 10 kΩ, not 103 Ω. The last character is always an exponent in 3- and 4-digit codes.
Reading EIA-96 as a plain code. "01B" is not a typo or a lot code; it is 100 × 10 = 1 kΩ. Two digits and a letter is the tell.
Expecting round numbers from E96. The series is 96 values per decade spaced by the 96th root of 10, each rounded to three figures. That is why you get 49.9 kΩ and 4.02 kΩ instead of 50 and 4. They are equally spaced on a log axis so adjacent 1 % ranges just touch. E24 and E12 are built the same way with fewer steps; 47, 51 and 56 are familiar only through repetition.