Resistor colour code calculator
Through-hole resistors have their value painted on in colour bands. Pick the colours and the calculator gives you the value, the tolerance and what your multimeter should read when you measure it; or type the value and it tells you which colours it should have. It works with 4, 5 and 6-band resistors and follows IEC 60062.
From colours to value
From value to colours
How to read a resistor
- Hold it the right way round. The tolerance band, nearly always gold or silver, goes on the right and is usually set slightly apart. The first band is the one closest to the left end. No resistor starts with gold or silver.
- Read the digits. On a 4-band resistor, the first two are digits; on a 5 or 6-band one, the first three.
- Apply the multiplier. The next band says how many zeros to add: black none, brown one, red two, orange three… Gold divides by 10 and silver by 100.
- Read the tolerance. Gold ±5 %, silver ±10 %, brown ±1 %, red ±2 %. On 6-band resistors, the last one is the temperature coefficient.
Example: yellow, violet, red and gold are 4, 7 and two zeros: 4700 Ω, that is 4.7 kΩ at ±5 %.
The colour table
| Colour | Digit | Multiplier | Tolerance |
|---|---|---|---|
| Black | 0 | ×1 | — |
| Brown | 1 | ×10 | ±1 % |
| Red | 2 | ×100 | ±2 % |
| Orange | 3 | ×1 k | ±0.05 % |
| Yellow | 4 | ×10 k | ±0.02 % |
| Green | 5 | ×100 k | ±0.5 % |
| Blue | 6 | ×1 M | ±0.25 % |
| Violet | 7 | ×10 M | ±0.1 % |
| Grey | 8 | ×100 M | ±0.01 % |
| White | 9 | ×1000 M | — |
| Gold | — | ×0.1 | ±5 % |
| Silver | — | ×0.01 | ±10 % |
A way to remember the order of the digits: the colours of the rainbow between black and white, with brown and red at the start (black, brown, red, orange, yellow, green, blue, violet, grey and white).
Why only certain values exist
Resistors are not made in any value, but in the preferred number series: E12 has 12 values per decade (10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82), E24 has 24 and E96, used for ±1 %, has 96. They are chosen so that, with their tolerance, they cover every value without gaps. If the colours give you a value that is in no series, you have most likely started from the wrong end or mixed up two similar colours (brown and red, or orange and yellow, in poor light). The calculator warns you.
Checking it with a multimeter
The colours say what the resistor should be; the multimeter says what it is. To measure it properly:
- Out of the circuit, or at least with one leg unsoldered: anything in parallel changes the reading.
- Without touching both legs with your fingers: your body, tens or hundreds of kΩ, ends up in parallel and upsets large values.
- On the ohms range with no power. The reading should fall within the tolerance margin the calculator gives you. If it reads OL, it is open; if much lower, it may be burnt or shorted.
You can practise with resistors R1, R2 and R3 on the component bench of the multimeter simulator.
And resistors with no colours
Surface-mount (SMD) resistors carry numbers instead of colours. With three digits, the first two are the value and the third the zeros: «472» is 4700 Ω. With four digits, the first three and the fourth: «4701» is 4.7 kΩ. An R marks the decimal point: «4R7» is 4.7 Ω. The same system is sometimes used on drawings: 4k7 is 4.7 kΩ and 2M2, 2.2 MΩ, and this calculator understands it too.
Common mistakes
- Reading it backwards: starting from the tolerance band gives absurd values.
- Mixing up brown, red and orange in poor light: when in doubt, measure it.
- Measuring it in circuit and trusting the reading.
- Forgetting the power rating: the colours do not say how many watts it can take. Its size does (1/4 W, 1/2 W, 1 W…), and it is worked out with the Ohm's law calculator.
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