The resistor color code calculator above runs in both directions. Decode a physical part by picking the colours you can see and it returns the resistance, the tolerance, the guaranteed minimum and maximum, and the temperature coefficient where a sixth band carries one. Or type the resistance you want, choose a tolerance, and it returns the band sequence you should be looking for in the drawer. Most colour code pages only do the first of those, which is the half you need once — the second half is the one you need every time you go looking for a part.
Arb Digital builds free calculators that follow the published standard rather than a half-remembered table. The colour assignments here follow IEC 60062, the international standard for marking codes on resistors and capacitors, including the pink multiplier for 10−3 that was added in the 2016 edition and that older charts simply do not have.
What This Resistor Color Code Calculator Does
In decode mode it takes each band as a separate dropdown, so you cannot accidentally enter a colour in a position where that colour is not legal. Black is a valid multiplier but never a valid first digit, gold and silver are valid multipliers and valid tolerances but never digits, and the dropdowns enforce that. The headline result is the nominal resistance, formatted with the appropriate prefix, and the grid gives the tolerance, the two extremes of the guaranteed range, and the temperature coefficient.
In encode mode it takes a resistance and a tolerance and works backwards. It reports the band colours in order, and it tells you if the value you asked for cannot be represented with the number of bands you selected. That happens more often than people expect: 4.75 kΩ is a perfectly ordinary precision value and it is impossible to mark on a four-band resistor, because four bands only carry two significant digits.
Both modes handle 3, 4, 5 and 6-band parts. Three bands is the old 20 per cent tolerance marking with no tolerance band at all. Four bands is the everyday 5 or 10 per cent part. Five bands is the precision part with three significant digits. Six bands adds the temperature coefficient in parts per million per kelvin.
How to Use It
- Choose the direction first. Decoding starts from a physical part in your hand. Encoding starts from a value in a schematic. The rest of the form changes to match.
- Count the bands before anything else. Miscounting is the single most common error, and it changes the answer by a factor of ten or more. Bands sit clustered toward one end of the body with a wider gap before the last one.
- Read from the crowded end. The digit bands are the tightly grouped ones. The tolerance band is separated by a visibly larger gap, and on most parts it is gold or silver.
- Set each band in decode mode, or the value and tolerance in encode mode. Every dropdown only offers colours that are legal in that position, so an impossible combination cannot be entered.
- Check the minimum and maximum in the grid. Those are the numbers your circuit actually has to tolerate. The nominal value is a label, not a measurement.
The Formula: How the Colour Code Is Read
Every colour carries a digit from zero to nine in the sequence black, brown, red, orange, yellow, green, blue, violet, grey, white. The digit bands are read left to right as an ordinary number, and the multiplier band is a power of ten applied to it: R = digits × 10multiplier.
On a four-band part there are two digits, so the value is (10d1 + d2) × 10m. Take the default, brown-black-red-gold: brown is 1, black is 0, giving the digits 10; red as a multiplier is 102, so the value is 10 × 100 = 1,000 Ω, or 1 kΩ. Gold as a tolerance band means ±5 per cent, so the part is guaranteed to lie between 950 and 1,050 Ω.
On a five-band part there are three digits: yellow-violet-black-brown-brown reads 4, 7, 0 with a multiplier of 101, giving 4,700 Ω at ±1 per cent. Note that the same 4.7 kΩ value appears as yellow-violet-red on a four-band part. Identical resistance, entirely different band pattern, because the digit count moved.
Gold and silver as multipliers mean 10−1 and 10−2, which is how sub-ten-ohm values are marked. IEC 60062:2016+AMD1:2019, Marking codes for resistors and capacitors, added pink as the 10−3 multiplier for milliohm-range parts, so a chart that stops at silver is out of date.
Tolerance Is the Number That Matters
The nominal resistance is a name for the part, not a claim about the part. What the manufacturer actually guarantees is that the true resistance lies inside the tolerance band around that nominal figure, and the grid on this page shows both ends of that interval because those are the values your circuit has to work with.
The tolerance colours are a different mapping from the digit colours and it is worth learning them separately: brown is ±1 per cent, red ±2, green ±0.5, blue ±0.25, violet ±0.1, grey ±0.01, gold ±5, silver ±10, and no band at all means ±20. Brown and red therefore mean one thing in a digit position and something completely different in the tolerance position, which is exactly why this tool asks for each band separately. Georgia State University's HyperPhysics page on carbon resistors sets out the same two tables side by side.
Tolerance stacks badly in dividers and bridges. Two 5 per cent resistors in a voltage divider give an output ratio that can be off by close to 10 per cent in the worst case, because one can be high while the other is low. If that matters for your circuit, run the extremes through the voltage divider calculator rather than assuming the nominal ratio holds.
Why Some Values Cannot Be Encoded
Resistors are not manufactured at arbitrary values. They come from the E-series of preferred numbers, which are geometric progressions chosen so that consecutive values differ by roughly the tolerance. E12, with twelve values per decade, pairs with 10 per cent parts. E24 pairs with 5 per cent. E96, with ninety-six values per decade, pairs with 1 per cent.
This has a direct consequence for encoding. A four-band resistor carries two significant digits, so it can only express E24 values and coarser. Ask for 4.75 kΩ on four bands and there is no legal answer — you need five bands, because 4.75 needs three digits. The calculator says so instead of quietly rounding to 4.7 kΩ and letting you order the wrong part.
The reverse trap catches people too. If a decoded value comes out as something that is not in any E-series, such as 1.13 kΩ from a four-band read, the bands were almost certainly misread. Genuine parts land on preferred values, so a value that is not a preferred value is a strong signal that the multiplier and tolerance bands got swapped.
The Sixth Band and Temperature Drift
The sixth band, present only on precision parts, gives the temperature coefficient of resistance in parts per million per kelvin. Brown is 100 ppm/K, red 50, orange 15, yellow 25, blue 10, violet 5 and grey 1. Manufacturers do vary on the less common colours, so for anything critical the datasheet beats the band.
The practical size of the effect is easy to underestimate. A 100 ppm/K part that warms 40 K above ambient drifts by 4,000 ppm, which is 0.4 per cent — comparable to the entire tolerance of a 0.5 per cent resistor. In a precision reference or a bridge, that drift is the dominant error long before the initial tolerance is. It is also the reason self-heating matters: work out the dissipation with the electrical power calculator before deciding a temperature coefficient is negligible.
Where This Sits Next to Our Other Electronics Tools
This page converts between a marking and a number. It does not do circuit arithmetic. Once you know the resistance, the Ohm's law calculator relates it to voltage and current, and the resistor combination calculator gives the equivalent resistance when you put several of them in series or parallel — which is the usual answer when the value you need is not a preferred value.
For the two most common jobs a single resistor does, the LED resistor calculator sizes a current-limiting resistor from a supply voltage and a forward voltage, and the voltage divider calculator handles the two-resistor ratio case. If you have a resistance in the wrong prefix, the resistance converter moves between milliohms, ohms, kilohms and megohms.
Arb Digital builds free tools like this one because useful pages earn attention. If you want tools, calculators or content built for your own audience, we can help.
Browse All Free Tools Talk to Arb DigitalCommon Mistakes to Avoid
- Reading the bands from the wrong end — start from the crowded end. Reading brown-black-red backwards as red-black-brown turns 1 kΩ into 200 Ω.
- Miscounting four bands as five — the digit count changes and the answer moves by a factor of ten. Look for the wider gap before the tolerance band.
- Using the digit table for the tolerance band — brown is 1 as a digit and ±1 per cent as a tolerance. Red is 2 and ±2 per cent. The two tables are unrelated.
- Treating the nominal value as exact — a 5 per cent 10 kΩ part is anywhere from 9.5 to 10.5 kΩ, and two of them in a divider can compound that error.
- Trusting colours on a scorched or aged part — heat browns the body and fades pigments, and red can read as orange under warm light. Measure with a meter when the part has been running hot.
Related Free Tools From Arb Digital
Take the decoded value into the Ohm's law calculator for voltage and current, or the electrical power calculator for dissipation and self-heating. Combine parts with the resistor combination calculator, size a current limiter with the LED resistor calculator, and check divider ratios with the voltage divider calculator. Change prefixes with the resistance converter. The full free online tools hub lists everything Arb Digital publishes.
Frequently Asked Questions
From the end where the bands are crowded together. The digit and multiplier bands sit close to one another, and there is a visibly wider gap before the tolerance band at the other end. On a four-band part the tolerance band is almost always gold or silver, and neither colour is ever a digit.
The number of significant digits. Four bands carry two digits, a multiplier and a tolerance. Five bands carry three digits, a multiplier and a tolerance, which is why precision parts use five. The same resistance therefore has two completely different band patterns depending on the band count.
It is the temperature coefficient of resistance in parts per million per kelvin. Brown is 100, red 50, orange 15, yellow 25, blue 10, violet 5 and grey 1. It tells you how much the resistance drifts as the part warms, which in a precision circuit is often a larger error than the initial tolerance.
Because the band count limits the number of significant digits. A four-band resistor carries only two, so a value like 4.75 kilohms cannot be marked on one at all. This calculator reports that as unencodable rather than rounding it to a different part number.
Gold multiplies by 0.1 and silver by 0.01, which is how resistances below ten ohms are marked. IEC 60062 also defines pink as a 0.001 multiplier for milliohm parts. In the tolerance position the same two colours mean plus or minus 5 per cent and 10 per cent instead.
Then there is no tolerance band and the part is a plus or minus 20 per cent type. Two digits and a multiplier are all that is marked. This is an older marking style and you will mostly meet it on legacy equipment rather than on anything currently manufactured.
Almost certainly a misread. Manufactured resistors come from the E-series of preferred numbers, so a genuine part lands on a standard value. A result such as 1.13 kilohms from a four-band read usually means the multiplier and tolerance bands were swapped or the reading direction was reversed.
This tool is provided for educational and workshop use. Colour assignments follow the published standard, but faded, scorched or non-standard markings do occur, so verify a critical part with a meter rather than relying on the bands alone.
