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Resistor Color Code Calculator

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A resistor is too small to print a number on, so its value is painted around it in coloured stripes: two or three digits, a power of ten, and how far from that figure the real part is allowed to be. Pick the colours you can see and this reads them back as a value — and because manufactured resistances come from fixed preferred series, it also tells you whether the value you have just read is one that anybody actually makes, which is the quickest way to catch a misread band.

Direction

Count the bands, including any that sit apart from the rest at one end.

Result

4.7 kΩ

±5% — anywhere from 4.465 kΩ to 4.935 kΩ

Exact value
4,700 Ω

Before tolerance

Standard series
E24

E6 (±20%), E12 (±10%), E24 (±5%)

Temperature coefficient
Not marked

Only 6-band parts carry one

Band by band

BandColourMeans
1YellowDigit 4
2VioletDigit 7
3Red× 100
4Gold±5%

Read the bands from the end where they are grouped together — the tolerance band sits on its own with a wider gap before it. If a resistor has been fitted the other way round, reading it backwards gives a value that is almost never in a standard series, which is what the series check above is for.

How to use the resistor color code calculator

  1. 1Count the bands on the part, including any that sits on its own with a wider gap before it.
  2. 2Choose that number from the dropdown — three, four, five or six.
  3. 3Set each band to the colour you can see, working from the end where the bands are grouped closest together.
  4. 4Read the value, the tolerance range and the temperature coefficient underneath.
  5. 5Check the standard-series line: if it says the value is not in any E series, a band has almost certainly been misread.
  6. 6Switch to "Value → colours" to go the other way and find the stripes for a resistance you need.

Examples

The most common resistor on any bench

Input
Yellow, violet, red, gold
Result
4.7 kΩ ±5%, anywhere from 4.465 kΩ to 4.935 kΩ

4 and 7 give 47, red multiplies by 100, gold means five percent. It is an E24 value, as a 5% part must be.

A precision five-band part

Input
Brown, black, black, brown, brown
Result
1 kΩ ±1%, from 990 Ω to 1.01 kΩ

Three digits give 100, the brown multiplier makes it ×10. Five-band parts carry an extra digit precisely so 1% values can be expressed.

Working backwards

Input
2.2 kΩ at ±5%
Result
Red, red, red, gold

The pleasing case where all three value bands are the same colour, which is why 2.2 kΩ is easy to spot in a drawer.

About the resistor color code calculator

How the bands encode a number

The scheme is positional, exactly like ordinary decimal notation. On a four-band part the first two bands are digits, using the sequence black, brown, red, orange, yellow, green, blue, violet, grey, white for zero through nine. The third band is a power of ten to multiply by, using the same colours for the same numbers with gold and silver added at the bottom for divide-by-ten and divide-by-hundred. The fourth is the tolerance.

Five-band parts insert a third digit before the multiplier and nothing else changes. That extra digit is what makes 1% values expressible: you cannot write 4.75 kΩ with two significant figures, and a 1% part whose value could only be given to two figures would be a contradiction. Six-band parts add a temperature coefficient after the tolerance, in parts per million per kelvin.

The colour order is not arbitrary — it broadly follows the visible spectrum from red through violet, with black and brown below and grey and white above. Once that is noticed, most of the sequence stops needing to be memorised, and the mnemonics people are taught in school become unnecessary.

Why the preferred-value check catches mistakes

Because resistors come only from the E series, the set of values that exist is far smaller than the set of values the colour code can express. That gap is a free error check. If a decode lands on 4.8 kΩ at 5% tolerance, no such part is made — E24 goes 4.3, 4.7, 5.1 — so either a band was read wrong or the resistor is not what it appears to be. This page tests every result against E6, E12, E24 and E96 and says which, if any, it belongs to.

The check is most valuable under exactly the conditions where misreading happens: poor light, an old part whose colours have darkened with heat, and the four pairs that genuinely look alike — brown against red, red against orange, blue against violet, and grey against silver on a body that has yellowed. A value that fails the series test is worth a second look before it is soldered in.

It is not infallible. Some values appear in more than one series and some deliberately odd parts exist, particularly current-sense resistors below an ohm and precision references above a megohm. Treat a failed check as a strong hint to measure the thing, not as proof that the reading is wrong.

Frequently asked questions

Which end do I start reading from?
From the end where the bands are bunched up. Manufacturers leave a noticeably wider gap before the tolerance band, so the stripes cluster towards one end and one sits apart at the other. Where that is genuinely hard to see, two other hints help: gold and silver only ever appear as a multiplier or a tolerance, never as a digit, so a gold band tells you which end you are at — and reading a part backwards nearly always produces a value outside every standard series, which this page flags.
What does the tolerance band actually promise?
That the part measured within that percentage of its marked value when it left the factory, at a stated temperature. It is not a running guarantee. Ageing, soldering heat and self-heating in operation all move a resistor slightly, and a sixth band, where present, quantifies the temperature part of that as parts per million per kelvin. For most circuits none of this matters; in a timing or measurement circuit it is the whole reason 1% parts exist.
Why are resistors made in odd values like 4.7 kΩ and 6.8 kΩ?
So that the tolerance bands of neighbouring values just meet without leaving gaps or overlapping wastefully. The E series are geometric: E24, used for 5% parts, steps by roughly 10% each time, which is about twice the tolerance. That way any resistance you might want is within tolerance of some stocked value, using as few distinct values as possible. The awkward-looking numbers are consequences of the twenty-fourth root of ten, rounded.
My resistor has only three bands. Is that a fault?
No — an absent fourth band is itself a specification, and it means ±20%. Parts that loose were common in older equipment and are rare now, because tighter manufacturing made 5% cheap enough that there was no reason to sell anything worse. If you have found one in an old chassis, treat its marked value as a very rough guide and measure it before relying on it.
What are the pale bands on a small surface-mount part?
Those are not colour codes at all. Surface-mount resistors are printed with numbers instead — three or four digits where the last is a multiplier, so 472 is 4.7 kΩ, or an EIA-96 code where two digits and a letter index a lookup table. The colour code exists because a cylindrical part can be read from any angle; a flat rectangle can just be printed on.

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