Resistor Colour Code

Understanding resistor colour codes is a fundamental electronics skill. Every through-hole resistor uses a series of coloured bands to encode its resistance value and tolerance, allowing you to identify components without any special equipment. Once you learn the system, reading a resistor takes only a few seconds.

How to Use the Resistor Colour Code Tool

1. Count the number of colour bands on your resistor (most have 4 or 5 bands).
2. Hold the resistor so the tolerance band (usually gold or silver) is on the right.
3. Enter each band colour from left to right into the tool.
4. The calculator will display the resistance value in ohms and the tolerance percentage.
5. Use the result to verify the component matches your circuit requirements.

The Formula

For a standard 4-band resistor, the formula is: Resistance = (Band 1 digit x 10 + Band 2 digit) x 10^(Band 3 multiplier).

Each colour maps to a digit: Black=0, Brown=1, Red=2, Orange=3, Yellow=4, Green=5, Blue=6, Violet=7, Grey=8, White=9. The multiplier band uses the same colours but represents powers of ten. For example, Red as a multiplier means x100. The fourth band is the tolerance: Gold = 5%, Silver = 10%, Brown = 1%.

For 5-band resistors (common in precision types), the first three bands are digits, the fourth is the multiplier, and the fifth is the tolerance.

Real-World Example

You find a resistor with bands: Yellow, Violet, Red, Gold.

• Band 1 (Yellow) = 4
• Band 2 (Violet) = 7
• Band 3 (Red multiplier) = x100
• Band 4 (Gold tolerance) = 5%

Resistance = (4 x 10 + 7) x 100 = 47 x 100 = 4,700 ohms (4.7 kilohms), with a 5% tolerance. This means the actual value falls between 4,465 ohms and 4,935 ohms.

Common Resistor Values in Electronics

Resistors follow the E-series of preferred values. The E12 series includes 12 values per decade (1.0, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2) and is standard for 10% tolerance components. The E24 series covers 24 values per decade for 5% tolerance parts. Knowing these series helps you quickly identify whether a resistor value is standard or unusual.

Frequently Asked Questions

What if I cannot tell the direction to read the bands? Look for a gold or silver band, which is almost always the tolerance band at the right end. If both ends look the same, try reading in both directions and check which result is a standard E-series value. The sensible reading is almost always the correct one.

What does tolerance mean in practice? Tolerance tells you how far the actual resistance can deviate from the marked value. A 470-ohm resistor with 5% tolerance could measure anywhere from 446.5 to 493.5 ohms. For most general circuits this range is perfectly acceptable; precision circuits may require 1% tolerance resistors.

Why do some resistors have 5 or 6 bands? Five-band resistors provide a third significant digit for greater precision. Six-band resistors add a sixth band that indicates the temperature coefficient (how resistance changes with temperature), expressed in parts per million per degree Celsius (ppm/C).

How do I measure a resistor if I cannot read the colour bands clearly? Use a digital multimeter set to resistance mode. Remove the resistor from any circuit first, as surrounding components can affect the reading. Touch the probes to each leg of the resistor and read the value directly from the display.

Reading a five-band resistor

A five-band resistor carries three significant digits instead of two, which is how precision parts get their extra figure. The first three bands are digits, the fourth is the multiplier and the fifth is the tolerance. Take a resistor banded yellow, violet, black, brown, brown.

The three digits give 470, the multiplier gives 4,700 ohms, and the tolerance gives a range of 4,653 to 4,747 ohms. Compare that with the four-band part in the example above, which is also 4,700 ohms on a 5% tolerance and spans 4,465 to 4,935 ohms. Same nominal value, and a 1% part narrows the range from 470 ohms wide to 94 ohms wide. That difference is what you pay for when a circuit needs a value to hold.

The third band is where most reading errors happen on a five-band part. Black in the third position means zero rather than nothing, so a resistor banded yellow, violet, black is 470 and not 47. A black band is easy to miss against a dark body, and reading it as absent shifts the value by a factor of ten.

The full colour table

Published tables disagree on the tolerance values for orange, yellow and grey: some list them, others leave them blank, and the figures quoted for grey range from 0.01% to 0.05%. That is why the table above marks those three as rarely used rather than printing a number. A part tolerance is read from the band, not from a chart, so if the band is orange and you need the exact figure, confirm it against the manufacturer's datasheet for that series.

Gold and silver only appear as multipliers on small values, which is how a 4.7 ohm part is banded yellow, violet, gold.

The decade series behind standard values

Resistor values are not spread evenly. They follow the E series, and the series count tells you how finely a decade is divided. The E12 series holds 12 values per decade for 10% parts, the E24 series holds 24 for 5% parts, and the E96 series holds 96 for 1% parts. Because the values repeat every decade, the same 12 or 24 numbers describe every order of magnitude.

The E12 numbers are 1.0, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8 and 8.2. The E24 series adds 1.1, 1.3, 1.6, 2.0, 2.4, 3.0, 3.6, 4.3, 5.1, 6.2, 7.5 and 9.1 to that list. The 4,700 ohm example sits on 4.7, which is in both series, so the value is standard in a 5% part and in a 1% part. Run the same test whenever a reading looks odd: the value should be a series value multiplied by a power of ten. A reading of 4,300 ohms is credible, and a reading of 4,100 ohms is not, because 4.1 is in neither the E12 nor the E24 list in that decade.

Tolerances, temperature and power

Three numbers decide whether a resistor will do the job, and the band colour gives only the first of them.

Tolerance sets the window around the nominal value. On a 4,700 ohm part, 1% spans 94 ohms, 2% spans 188 ohms, 5% spans 470 ohms and 10% spans 940 ohms. Choose the tolerance from the circuit rather than from the shelf: a voltage divider feeding an analogue input needs a tighter pair than an indicator LED.

Power sets how much heat the body can shed. A 4,700 ohm resistor carrying 12 volts drops 2.553 milliamps and dissipates 30.64 milliwatts, which is 12.26% of a quarter-watt rating and comfortable. Raise the supply to 24 volts and the same part dissipates 122.55 milliwatts, half the rating, and the body will run warm. The current rises with voltage and the power rises with the square of it, so a doubling of voltage quadruples the heat.

Temperature coefficient sets how much the value drifts as the part warms. The sixth band on a precision resistor gives this figure in parts per million per kelvin. A 100 ppm/K part moving 40 degrees changes by 0.4%, which is 18.8 ohms on a 4,700 ohm resistor. A 250 ppm/K part over the same rise changes by 1%, or 47 ohms, which is wider than the 1% tolerance band the part was sold with. In a circuit that runs hot, the drift matters more than the marked tolerance.

The standard behind the colour code

The colour code is an international standard rather than a convention. IEC 60062, Marking codes for resistors and capacitors, defines the colour code for fixed resistors and states that it is intended for use with the values of the E6 to E192 series specified in IEC 60063. The current edition is IEC 60062:2016, with Amendment 1 published in 2019, and the fifth edition of 2004 was withdrawn on 12 July 2016.

The 2016 edition added pink as a code for a multiplier of 10 to the power minus three, which is the band you will occasionally see on a sub-ohm part. It also separated the rules for colour assignment, value and tolerance coding and temperature coefficient coding into their own clauses. Where a resistor datasheet and a wall chart disagree, the datasheet is describing the specific part and the standard is describing the system.

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