Resistor color code calculator
| Colour | Digit | Multiplier | Tolerance |
|---|---|---|---|
| Black | 0 | ×1 | — |
| Brown | 1 | ×10 | ±1% |
| Red | 2 | ×100 | ±2% |
| Orange | 3 | ×1k | — |
| Yellow | 4 | ×10k | — |
| Green | 5 | ×100k | ±0.5% |
| Blue | 6 | ×1M | ±0.25% |
| Violet | 7 | ×10M | ±0.1% |
| Grey | 8 | ×100M | ±0.05% |
| White | 9 | ×1G | — |
| Gold | — | ×0.1 | ±5% |
| Silver | — | ×0.01 | ±10% |
Brown-black-red-gold is 1 kΩ at ±5%: brown is 1, black is 0, red multiplies by 100, gold is the tolerance. Four bands carry two significant digits; five and six carry three, and the sixth adds temperature coefficient. The reverse mode turns 4,700 Ω back into yellow-violet-red-gold.
How to read a resistor
The colour code exists because a resistor is too small to print a number on legibly, and it survives because it can be read from any angle. Its weaknesses are well known: brown, red and orange are hard to tell apart under warm light, and on a 4-band resistor with no clear tolerance band it is genuinely ambiguous which end to start from. The rule of thumb is that the tolerance band sits slightly further from its neighbours, and that a reading which produces a nonsense value — 47 MΩ where a pull-down should be — means you read it backwards.
The band count itself tells you something before you read a single colour. Two significant digits is exactly enough for the E12 and E24 series that make up ordinary 5% and 2% stock: every E12 value has two digits, from 10 through 82. A part that needs three digits, such as 4.99 kΩ or 2.21 kΩ, belongs to the tighter E48 or E96 series and will carry five bands instead. The practical difficulty with five bands is that the tolerance band is often brown, the same colour as a digit, so there is no gold or silver to anchor the orientation; the tie-breaker is the wider gap before it.
A sixth band gives temperature coefficient in parts per million per degree, and it matters more often than people expect. A 0.1% resistor with a 100 ppm coefficient drifts by 0.1% over a ten-degree change, doubling its error before anything else has happened. That is why reference dividers and current shunts specify low-ppm parts, and why matched pairs on one substrate are used where the ratio matters more than the absolute value: both resistors drift together and the ratio holds.
The reverse direction is the useful one when you are picking a part out of a tray rather than identifying one in hand, and it is the faster way to spot a mistake. Knowing that 220 Ω should be red-red-brown makes an incorrectly stuffed board obvious at a glance, without a meter. Not every value has a valid code: four bands cannot express 4.99 kΩ, and the tool rounds to what two digits allow.
What people use it for
- Identifying a resistor from a drawer
- Checking a board against its schematic
- Learning the code for an exam
- Confirming a value before soldering
- Reading ordinary 5% four-band stock
- Reading a 1% precision part from the E96 series
- Estimating drift on a six-band part over its temperature range
- Finding the band sequence for a value you need
- Sorting a mixed bag of loose resistors into a parts drawer
- Choosing a part for a voltage reference or a current shunt
- Checking a kit against its parts list before assembly
Questions
The tolerance band is usually gold or silver and sits slightly apart from the others. Put it on the right and read toward it. On a five or six band part the tolerance is often brown, the same colour as a digit, so the wider gap before the last band is the only orientation cue you get.
4.7 kΩ at ±5%. Yellow is 4, violet is 7, red multiplies by 100, so the real value lies between 4.465 and 4.935 kΩ.
Yellow, violet, red, gold for 4.7 kΩ at 5%; red, red, brown, gold for 220 Ω. The second is worth memorising, because it is the most common LED resistor there is.
Four band gives two significant digits, five gives three. Two digits reach only as far as the E24 series, which is why 5% stock is four bands and precision parts such as 4.99 kΩ need five. The reverse is not true: 1 kΩ is marked either way, and a five-band round value is simply promising a tighter tolerance.
1 kΩ at ±1%. The three digits are 1, 0, 0 and the fourth brown multiplies by 10.
Temperature coefficient in ppm per degree Celsius. Brown is 100, red 50, orange 15, yellow 25, blue 10, violet 5.
0.01% per degree, so a 20 degree swing is 0.2%, often larger than the resistor’s initial tolerance. It only matters where absolute accuracy over temperature does: for a pull-up or an LED resistor it is irrelevant.
A ±20% tolerance. It is rare on modern parts but common on old stock. Where the band is there, a four-band part is usually gold for 5% or silver for 10%.
As a multiplier it means ×0.1, so brown-black-gold is 1 Ω. As the fourth band it means ±5% tolerance.
Because the E48 and E96 precision series contain values like 4.99 and 2.21 that two digits cannot express.
Because they genuinely do under warm lighting on a small part. Use daylight, or measure it.
Not in four bands. Values needing three significant digits require a five-band code.
4700. The letter marks the decimal point in the shorthand, so 4k7 is 4.7 kΩ.
The bands can only express what the series holds. Take the nearest E12 or E24 value and check the difference matters before you go looking for a special part; for a pull-up or an LED resistor it almost never does.
Where a ratio matters, yes. Two resistors on the same substrate drift together, so a divider holds its ratio even as both values move. Low ppm is what you want when the absolute value has to stay put.