Resistor Color Code Calculator

What the resistor color code calculator does

Resistors are marked with colored bands that encode their value, and this calculator decodes them. Select the number of bands and the color of each, and it returns the resistance, the tolerance, the value range, and where applicable the temperature coefficient.

Below is what the color code is, how the bands are read, what the different band counts mean, and a worked example.

How to use it

1. Select the number of bands: four, five, or six.
2. Choose the color of each band from the drop-downs.
3. Press Calculate for the resistance and tolerance, or Reset to clear it.

What the resistor color code is

The resistor color code is a system of colored bands printed around a resistor to show its value. Because resistors are usually too small to print numbers on clearly, and because bands can be read from any angle, the color code became the standard way to mark them. Each color stands for a number, and the bands are arranged so that, read in order, they spell out the resistance, how precise it is, and sometimes how it behaves with temperature. It is one of the first things anyone working with electronics learns to read.

The code follows an internationally agreed standard, so a resistor made anywhere can be read the same way. Once you know what each color means and the order the bands come in, you can read any resistor at a glance. The system uses the same ten colors for digits, from black for zero up to white for nine, in the order of the rainbow with black and white at the ends, plus a few extra colors for multipliers and tolerances. This calculator does the decoding for you, turning a sequence of colors into the resistor's value.

How the bands are read

The bands are read in order from one end, and each has a specific job. The first bands give the significant digits of the value, simply the numbers, read straight off using the color-to-number mapping. After the digit bands comes the multiplier band, which tells you what power of ten to multiply those digits by, setting the overall scale from fractions of an ohm up to millions. Together, the digits and the multiplier give the resistance.

For example, the digit colors follow a fixed sequence: black is zero, brown one, red two, orange three, yellow four, green five, blue six, violet seven, gray eight, and white nine. The multiplier band uses the same colors to mean powers of ten, with gold and silver added for dividing by ten or a hundred, allowing small values. After the multiplier comes the tolerance band, and on some resistors a final band for temperature behaviour. Reading them in sequence reconstructs the full specification, which is exactly what the calculator does from the colors you select.

Four, five, and six bands

Resistors come with different numbers of bands depending on how precisely their value needs to be specified. A four-band resistor, the most common and the simplest, uses two digit bands, a multiplier, and a tolerance band. Two significant digits are enough for everyday resistors where exact precision is not critical, and this is the scheme most hobbyists meet first.

Five-band and six-band resistors are used where more precision is needed. The five-band type adds a third digit band, giving three significant digits instead of two, which allows finer value distinctions, common in precision resistors. The six-band type adds yet another band beyond that for the temperature coefficient, which describes how much the resistance drifts as temperature changes, important in circuits that must stay accurate across a range of conditions. The calculator handles all three schemes, adjusting the bands it asks for based on the count you select, so you can decode whichever kind of resistor you have.

Tolerance and temperature coefficient

Beyond the resistance value itself, the color code carries information about how much that value can be trusted. The tolerance band states how far the actual resistance may stray from its nominal value, given as a percentage. A resistor marked with a five percent tolerance, for instance, may be up to five percent above or below its stated value, so the calculator reports not just the nominal resistance but the range it could fall within. Tighter tolerances, down to a fraction of a percent, are shown by their own colors.

The temperature coefficient, present on six-band resistors, describes how the resistance changes as the resistor heats or cools, expressed in parts per million per degree. A low coefficient means the resistor holds its value steadily across temperature, which matters in precision and measurement circuits. Most everyday resistors do not specify this and have only four or five bands. By reporting the tolerance range and, where given, the temperature coefficient, the calculator provides the full picture of what a resistor's color code is telling you, not just its headline value.

Units and precision

The calculator takes the number of bands and the color of each band, and returns the resistance in ohms, the tolerance as a percentage, the resulting value range, and the temperature coefficient for six-band resistors. It follows the standard color-to-number assignments used internationally. The decoding is exact; the tolerance range simply reflects the percentage the resistor's own band specifies, showing the lowest and highest values it is guaranteed to fall between.

A worked example

Suppose a four-band resistor has bands of brown, black, red, and gold.

The first two bands, brown and black, give the digits one and zero, making 10. The red multiplier band means multiply by a hundred, so the resistance is 10 × 100 = 1,000 ohms, or 1 kilohm. The gold tolerance band means five percent, so the actual value lies between about 950 and 1,050 ohms. A five-band precision resistor would work the same way but with three digit bands for a more exact value.

Questions people ask

How do you read a resistor color code?

Read the bands in order: the first ones are digits, then a multiplier (a power of ten), then the tolerance. Each color maps to a fixed number.

What do the colors mean?

For digits: black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, gray 8, white 9. The same colors mean powers of ten for the multiplier band.

What is the difference between four, five, and six bands?

Four bands give two digits plus a multiplier and tolerance; five bands add a third digit for precision; six bands add a temperature coefficient.

What does the tolerance band tell you?

How far the real resistance may differ from the marked value, as a percentage. A five percent band means the value can be five percent above or below nominal.

References

A quick note on where this comes from. The resistor color code follows the international standard IEC 60062, and the color-to-number scheme is documented widely in electronics references. The underlying resistance and tolerance concepts are standard, as covered in OpenStax's University Physics.

1. International Electrotechnical Commission, IEC 60062, Marking codes for resistors and capacitors. https://www.iec.ch/
2. Wikipedia, Electronic color code. https://en.wikipedia.org/wiki/Electronic_color_code
3. OpenStax, University Physics Volume 2, Section 9.3, Resistivity and Resistance. https://openstax.org/books/university-physics-volume-2/pages/9-3-resistivity-and-resistance