Resistor colour code

Introduction

Through-hole resistors are too small to print a value on, so they carry coloured bands instead. Each colour stands for a digit, a power of ten, a tolerance or a temperature coefficient, following the international standard IEC 60062. Reading them quickly is a basic skill on the bench, and checking a reading avoids the classic mistake of fitting a 47 kΩ part where 4.7 kΩ was meant.

This calculator reads 4, 5 and 6-band resistors. It gives the value, the tolerance, the lowest and highest values within tolerance, the temperature coefficient of six-band parts, and which standard E series the value belongs to. It also works the other way: enter a resistance and it lists the bands to look for. It is for students, hobbyists, technicians and anyone sorting a drawer of resistors.

Formulas

The colour code (IEC 60062):

black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8, white 9

Resistance:

4 bands:     R = (10 d₁ + d₂) × 10^m
5 or 6 bands: R = (100 d₁ + 10 d₂ + d₃) × 10^m

Multiplier band m: silver −2, gold −1, then the digit colours black 0 to white 9.

Tolerance band: brown ± 1 %, red ± 2 %, green ± 0.5 %, blue ± 0.25 %, violet ± 0.1 %, gold ± 5 %, silver ± 10 %, no band ± 20 %.

Range within tolerance:

R_min = R (1 − t),   R_max = R (1 + t)

Sixth band, temperature coefficient in ppm/K: black 250, brown 100, red 50, yellow 25, green 20, orange 15, blue 10, violet 5, grey 1.

Assumptions and limitations

• The colours follow IEC 60062:2016. Orange, yellow and grey tolerance bands have had different meanings in different editions, so they are not offered.
• Four-band resistors carry two significant digits and five- and six-band parts three. A value that needs more digits is rounded and flagged.
• Read from the end where the bands are grouped together. The tolerance band is usually set slightly apart, and gold or silver never comes first.
• Faded or heat-darkened bands are easy to misread, particularly red, orange and brown. When in doubt, measure the resistor out of circuit with a meter.
• The tolerance applies at 25 °C. The temperature coefficient adds its value in parts per million for every kelvin away from that.

Worked example

A resistor has four bands: yellow, violet, red, gold. What is it?

1. First digit: yellow = 4. Second digit: violet = 7. Together they make 47.
2. Multiplier: red = 10², so the value is 47 × 100 = 4 700 Ω = 4.7 kΩ.
3. Tolerance: gold = ± 5 %.
4. Lowest value within tolerance: 4 700 × 0.95 = 4.465 kΩ. Highest: 4 700 × 1.05 = 4.935 kΩ.
5. 4.7 kΩ is in the E6 series, the most common values of all, and so in E12 and E24 as well.

A five-band resistor reading brown, black, black, brown, brown is 100 × 10¹ = 1 kΩ ± 1 %. Adding a red sixth band means a temperature coefficient of 50 ppm/K.

FAQ

Related calculators

• Ohm's law and electrical power — what the resistor does in the circuit.
• Voltage divider — choosing standard values for a target voltage.
• LED series resistor — another common resistor to identify.
• Series and parallel resistors — combining parts to reach a value you don't have.