What the Resistor Color Code Calculator does
This calculator turns resistor colour bands into a resistance, a tolerance and a temperature coefficient, and turns a value back into the bands you should be looking for. Pick the colours you can see and the value appears straight away, with the band diagram redrawn so you can check you read them in the right order.
The colours are not arbitrary. IEC 60062 fixes them: black is 0 and white is 9, running through the spectrum in between, with gold and silver reserved for fractional multipliers and loose tolerances. Once that table is in front of you the only real difficulty left is deciding which end of the part to start from.
How to use it
- Hold the resistor so the tolerance band - usually gold or silver, and often set slightly apart from the others - is on the right.
- Choose 3, 4, 5 or 6 bands. Four is the common 5% part; five and six are precision parts with a third significant digit.
- Set each band's colour from left to right. The value, tolerance range and nearest preferred value update as you go.
- Check the band diagram against the part in your hand. If the colours look reversed, read it from the other end - the value you get will usually be an implausible one, which is the giveaway.
- To go the other way, open "Work backwards" and type a value such as 4k7; the bands you need are drawn for you.
Reading the results
The tolerance is a manufacturing window, not drift. A 1 kOhm 5% resistor may leave the factory anywhere between 950 and 1,050 Ohm, and it will stay near wherever it landed.
The temperature coefficient on a six-band part is separate from tolerance: 100 ppm/K over a 50 K rise is another 0.5%, on top of the initial tolerance.
If the value you decode is not close to a preferred value for that tolerance class, you have almost certainly read the bands backwards or mistaken red for brown. The calculator shows the nearest E-series value so you can spot this immediately.
Worked example: brown, black, red, gold
Brown is 1 and black is 0, so the significant digits are 10. Red as the third band is a multiplier of 100, giving 10 x 100 = 1,000 Ohm. Gold as the fourth band is +/-5%.
The part is therefore 1 kOhm +/-5%, so anything from 950 to 1,050 Ohm is within specification. 1 kOhm is a member of E24, the 5% series, which is exactly what you would expect for a gold-banded part.
Read the same resistor from the wrong end and you get gold, red, black, brown: gold first is not a valid digit, so the calculator refuses it rather than inventing a number - which is itself the clue that the part is the other way round.
Formulas and scoring rules
- Value from bands
R = (significant digits) x multiplierTwo digits on a 3 or 4 band part, three on a 5 or 6 band part.- Tolerance window
Rmin = R x (1 - t/100), Rmax = R x (1 + t/100)t is the tolerance band's percentage; a part with no tolerance band is +/-20%.- Temperature drift
dR/R = tempco[ppm/K] x dT / 1,000,000100 ppm/K over a 50 K rise is 0.5% - independent of, and added to, the initial tolerance.- Multiplier colours
black x1, brown x10, red x100, orange x1k, yellow x10k, green x100k, blue x1M, violet x10M, grey x100M, white x1G, gold x0.1, silver x0.01- Tolerance colours
brown 1%, red 2%, green 0.5%, blue 0.25%, violet 0.1%, grey 0.05%, gold 5%, silver 10%, none 20%
Which way round does a resistor read?
There is no marking that says "start here", so you use the conventions. The tolerance band is the one that is gold or silver, and on most parts there is a visibly wider gap before it. On a body-coloured precision part the tolerance band is often at the end nearest the lead-out.
If both ends look the same, decode it both ways and keep the reading that lands on or near a preferred value. Resistors are made to the E series, so 27 kOhm is plausible and 72 kOhm is not. That single check catches almost every reversed reading.
Why some values simply do not exist
IEC 60063 lays out the preferred number series - E6, E12, E24, E48, E96 - each spaced so that consecutive values just overlap at the tolerance of that class. E24 has 24 values per decade for 5% parts; E96 has 96 for 1% parts. A 5% part is not made at 3.2 kOhm because 3.0 and 3.3 already cover that ground within their tolerance.
This calculator shows the nearest member of the appropriate series for the tolerance you selected, which is both a sanity check on your reading and the value to order when a circuit calls for something between two standard parts.
Limitations: what the result does not prove
- It reads the marking, not the resistor. Only a meter tells you what the part in front of you actually measures, and a resistor that has been overheated can sit well outside its printed tolerance.
- Colour under artificial light is unreliable: brown and red, and orange and yellow, are routinely confused on small parts. When it matters, measure.
- The five-band scheme has an ambiguity the standard does not resolve: a body-coloured part with bands that could be read either way needs the preferred-value check described above.
- Some military and older parts use extra bands for reliability or mil-spec failure rates rather than temperature coefficient, and this calculator does not decode those.
Privacy: where your data goes
Everything you paste, type or drop is processed in this browser tab. It is not uploaded, logged, stored or sent to analytics. Session recording and tag-manager scripts are switched off on this page.
Standards and sources
- IEC 60062 - Marking codes for resistors and capacitors - checked 19 Sep 2026
- IEC 60063 - Preferred number series for resistors and capacitors (E series) - checked 19 Sep 2026
- Vishay - Resistor colour code and marking application note
Frequently asked questions
What do the colours on a resistor mean?
Each colour is a digit from black (0) to white (9), following the spectrum. The band after the digits is a power-of-ten multiplier, and the band after that is the tolerance, where gold is 5% and silver is 10%. A sixth band, when present, gives the temperature coefficient in parts per million per kelvin.
How do I know which end of a resistor to start reading?
Put the tolerance band on the right. It is the gold or silver one, and there is usually a wider gap between it and the rest. If neither end looks like a tolerance band, decode it both ways and keep the reading that lands on a standard E-series value.
What does a resistor with no fourth band mean?
A part with three bands has no tolerance band, and IEC 60062 reads that as +/-20%. These are rare in new equipment but common in old consumer electronics, where 20% parts were entirely normal.
What is the difference between a four-band and a five-band resistor?
Four bands give two significant digits and are normally 5% or 10% parts. Five bands give three significant digits, so a 1% part can be marked 1.47 kOhm rather than being rounded to 1.5 kOhm. A sixth band adds the temperature coefficient.
Why is gold sometimes a multiplier and sometimes a tolerance?
Its position decides. In the multiplier position gold means x0.1 and silver x0.01, which is how sub-ohm values such as 5.6 Ohm and 0.22 Ohm are marked. In the tolerance position the same colours mean 5% and 10%. Counting bands from the correct end is what tells them apart.
What does 100 ppm/K on a resistor mean in practice?
The resistance changes by 100 parts per million for every kelvin of temperature change - 0.01% per degree. Over a 50 K rise inside an enclosure that is 0.5%, which matters in a precision divider or a current sense and is irrelevant in a pull-up.
Can this calculator tell me the power rating?
No, and nothing can from the bands: power rating is set by the physical size of the body, not by the colours. As a rough guide a 6.3 mm body is typically 1/4 W and a 9 mm body 1/2 W, but the manufacturer's data sheet is what settles it.
Why does my meter read a different value from the bands?
First check the tolerance window shown above - a 5% part is allowed to be 5% out. Then check that the resistor is out of circuit, since anything in parallel with it drags the reading down, and that your fingers are not across the probes on a high-value part.
Last reviewed by the A2Z.Tools team against the sources listed above.
