Resistor Colour Code Calculator

Decode 4, 5 and 6-band resistors — or find the bands for any value.

Decode a 4-band resistor's color bands into its resistance and tolerance.

Formula

R = (10 × digit1 + digit2) × multiplier

Inputs

Band 1 (1st digit)
Band 2 (2nd digit)
Band 3 (multiplier)
Band 4 (tolerance)

What it does

Through-hole resistors show their value as coloured bands. This tool decodes 4-, 5- and 6-band resistors and also works in reverse: type a value and it shows the bands.

Where it's used

Identifying loose parts, checking a board against its bill of materials, and reading salvaged components.

How to use it

Choose the number of bands.
Hold the resistor with the tolerance band (often gold or silver, set slightly apart) on the right.
Select each colour from left to right and read the value and its min–max range.
For the reverse lookup, type a value such as 4k7 in the last field.

The formula explained

Digit bands: black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8, white 9
Multiplier: power of ten to multiply by; gold = ×0.1, silver = ×0.01
Tolerance: how far the real value may differ: brown ±1 %, gold ±5 %, silver ±10 %
Tempco: 6th band: drift in ppm per °C

Worked example

A 5-band resistor: brown, black, black, red, brown.

Inputs:

Number of bands: 5 bands
Band 1 (1st digit): Brown (1)
Band 2 (2nd digit): Black (0)
Band 3 (3rd digit): Black (0)
Multiplier: Red (×10^2)
Tolerance: Brown (±1%)

The calculator gives:

Resistance: 10 kΩ
Minimum: 9.9 kΩ
Maximum: 10.1 kΩ

Tips and common mistakes

5- and 6-band resistors are precision parts (usually ±1 % or better).
Red/orange and brown/red are easy to confuse under warm light — confirm with a multimeter.
Measure out of circuit: other parts in parallel make the meter read low.

Questions people ask

What do the colours stand for?

Black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8, white 9. As a multiplier, gold means ×0.1 and silver ×0.01; as a tolerance band, gold is ±5 % and silver ±10 %.

Which end do I read from?

Start at the end where the bands are bunched together. The tolerance band (often gold or silver) is set slightly apart at the other end. If your reading gives a value that isn’t a standard one, try reading from the other side.

What value is yellow, violet, red, gold?

Yellow 4 and violet 7 give 47, red multiplies by 100, so it is 4 700 Ω = 4.7 kΩ. Gold is ±5 %, so the real value lies between 4.465 kΩ and 4.935 kΩ.

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