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Resistor Color Code Calculator

A resistor’s value is printed as coloured bands. Each colour is a digit, and one band is a multiplier. Brown (1), black (0), red (× 100), gold reads 10 × 100 = 1 kΩ with a tolerance of ±5 %. Choose the colours to get the value, or type a value to get the colours. It works for 4-band, 5-band and 6-band resistors.

Result

Resistance

1 kΩ ±5 %

Tolerance: ±5 %
The real value is between: 950 Ω and 1.05 kΩ

Band by band

Band 1: Browndigit: digit 1
Band 2: Blackdigit: digit 0
Band 3: Redmultiplier: × 100
Band 4: Goldtolerance: ±5 %

If the first band is hard to tell from the last, remember the tolerance band is usually gold or silver and sits a little apart from the others.

The formula

A 4-band resistor: two digits and a multiplier

\htmlData{sym=R}{R} = \left(10\,\htmlData{sym=B_1:band}{B_1} + \htmlData{sym=B_2:band}{B_2}\right) \times \htmlData{sym=M:band}{M}

A 5-band or 6-band resistor: three digits and a multiplier

\htmlData{sym=R}{R} = \left(100\,\htmlData{sym=B_1:band}{B_1} + 10\,\htmlData{sym=B_2:band}{B_2} + \htmlData{sym=B_3:band}{B_3}\right) \times \htmlData{sym=M:band}{M}

The range the real resistance falls in

\htmlData{sym=R_tol}{R_{\mathrm{tol}}} = \htmlData{sym=R}{R}\left(1 \pm \dfrac{\htmlData{sym=p:tol}{p}}{100}\right)

What each letter means

$R$: Resistance (Ω · ohm) : How strongly something opposes current.
$B_1$: First digit band (no unit) : The digit that the first colour band stands for (brown is 1, red is 2 …).
$B_2$: Second digit band (no unit) : The digit that the second colour band stands for.
$M$: Multiplier (no unit) : What the digits are multiplied by: 10 to the power the multiplier colour says (red is × 100, gold is × 0.1).
$B_3$: Third digit band (no unit) : The digit that the third colour band stands for (5-band and 6-band resistors only).
$R_{\mathrm{tol}}$: Lowest or highest resistance (Ω · ohm) : The two ends of the range the real resistance falls in, given the tolerance.
$p$: Tolerance (% · percent) : How far from its marked value the part may be, in percent. A 5 % resistor marked 1 kΩ is somewhere from 950 Ω to 1050 Ω.

How it works

The colours are the same on every resistor (the IEC 60062 standard). Black is 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8 and white 9. On a 4-band resistor the first two bands are digits, the third is the multiplier (the digits times ten to the power of the colour’s number, so red is × 100), and the fourth is the tolerance. Gold as a multiplier means × 0.1 and silver × 0.01, which is how values below 10 Ω are written.

A 5-band resistor, used for precise parts, has three digit bands, then the multiplier, then the tolerance. A 6-band resistor adds a last band for the temperature coefficient: how many parts per million the resistance drifts for each kelvin of temperature change. The tolerance colours are brown ±1 %, red ±2 %, green ±0.5 %, blue ±0.25 %, violet ±0.1 %, grey ±0.05 %, gold ±5 % and silver ±10 %. A 4-band resistor with no tolerance band is ±20 %.

Hold the resistor so the tolerance band (often gold or silver, set a little apart from the rest) is on the right, and read from the left. In the other direction, the calculator splits your value into digits and a multiplier, and warns you when the value is not one that is normally made. Standard values come from the E12 series (±10 % and ±5 %), the E24 series (±5 %) and the E96 series (±1 % and better).

Worked example

Brown, black, red, gold. Brown is 1 and black is 0, so the digits are 10. Red as a multiplier is × 100. So the value is 10 × 100 = 1 kΩ. Gold means ±5 %, so the real value is between 950 Ω and 1.05 kΩ.
Five bands: brown, black, black, brown, brown. The digits are 1 0 0, and brown as a multiplier is × 10. So 100 × 10 = 1 kΩ, and the last brown means ±1 %. Same value as before, but held more tightly.
The other way: 4.7 kΩ is 47 × 100. Yellow is 4, violet is 7 and red is × 100, so the bands are yellow, violet, red, then gold for ±5 %. The calculator reads that back as 4.7 kΩ.
Below 1 Ω you need silver. 0.47 Ω is 47 × 0.01: yellow, violet, silver, with silver as the × 0.01 multiplier.

Common questions

How do I know which end to start reading from?

Start from the end where the bands are closer together. The tolerance band is usually gold or silver and has a bigger gap in front of it, so it should end up on the right. Gold and silver are never the first band, because they are not digits. If you are unsure, measure the resistor with a multimeter: the calculator tells you which reading to expect.

What if the colours do not make a standard value?

Then either a band was misread (brown and orange, or red and orange, look alike in poor light) or the part is not a common one. In the value-to-colours mode, the calculator warns when your value is not in the E12, E24 or E96 series and shows the nearest standard values.

What is the sixth band for?

It gives the temperature coefficient in ppm/K. A resistor with 100 ppm/K changes by 0.01 % for each kelvin, so 50 K of warming moves a 1 kΩ resistor by about 0.5 Ω. Most circuits never notice. Precision circuits, such as measuring instruments, choose 25 ppm/K or 10 ppm/K parts.

Try it live

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