Resistor decoder
Colour bands or SMD markings to a resistance, with tolerance range and the nearest preferred values.
Colour bands for through-hole parts, SMD code for the printed markings on chip resistors.
A fourth band is tolerance and a fifth adds a third significant digit — 5-band parts are the 1 % ones. Some precision resistors add a sixth band for temperature coefficient, which this does not decode.
Significant figure 1, read from the end furthest from the tolerance band. Brown-black is 10, and the multiplier does the rest.
Significant figure 2, read from the end furthest from the tolerance band. Brown-black is 10, and the multiplier does the rest.
The power of ten the digits are multiplied by. Gold and silver are the negative ones: ×0.1 and ×0.01, for values below 10 Ω.
The tolerance band, set slightly apart from the rest — that gap is how you tell which end to read from. Gold is ±5 %, brown ±1 %, red ±2 %.
- 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
What it computes
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 ×100k3-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.
Worked example
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 kΩSame 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 kΩEntering 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 it stops being valid
- 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 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.
Further reading
- IEC 60062:2016— the marking standard itself: colour code, alphanumeric code, date codes.
- IEC 60063:2015— the E-series preferred numbers and how each series is derived.
- IEC 60062:2016, Marking codes for resistors and capacitors— the standard behind the colour bands, the three- and four-digit SMD codes and the EIA-96 two-digit-plus-letter scheme.