100 Ω resistor colour code
brownblackbrowngold
100 Ω ±5%
brown black brown gold — four bands, read from the end with the bands closest to it.
| Band 1 — first digit | brown = 1 |
| Band 2 — second digit | black = 0 |
| Band 3 — multiplier | brown × 10 |
| Band 4 — tolerance | gold ± 5% |
| Value | 100 Ω |
| Acceptable range | 95 Ω to 105 Ω |
Reading it
The two digit bands give 10 and the multiplier band multiplies it by 10:
10 × 10 = 100 Ω
Which end to start from is the part that catches people. The tolerance band is the one set slightly apart from the other three, and it is gold or silver far more often than not — neither of which is a digit colour, so a gold or silver band tells you which end you are at. Read from the opposite end.
What ±5% actually means
A 100 Ω ±5% resistor is in specification anywhere from 95 Ω to 105 Ω. A meter reading of 95 Ω on this part is not a fault and not a reason to replace it.
100 Ω is one of the E24 values — the 24 steps per decade that ±5% resistors are made in. The steps are spaced so that the tolerance bands of neighbouring values just about touch: there is no gap between one value's range and the next, and no point making anything in between. It is the same reasoning that gives ±10% parts only 12 values per decade.
The same resistor with five bands
Precision resistors carry five bands: three digits, a multiplier and a tighter tolerance. The same 100 Ω reads
brownblackblackblackbrown
— brown black black black brown. The digits become 1, 0 and 0, and the multiplier drops one decade to black to compensate. The brown final band is ±1% rather than ±5%, which narrows the range to 99 Ω–101 Ω.
How much this one can take
A resistor's limit is heat, not voltage or current on their own: the power it turns into heat is V² ÷ R, so the same wattage allows very different numbers at 100 Ω than it does at a value ten times away. This is the part of a colour code lookup people actually came for and charts leave out.
| Rating | Maximum current | Maximum voltage |
|---|---|---|
| ⅛ W | 35.4 mA | 3.5 V |
| ¼ W | 50 mA | 5 V |
| ½ W | 70.7 mA | 7.1 V |
| 1 W | 100 mA | 10 V |
The quarter-watt part is the one in everybody's drawer: at 100 Ω it will carry 50 mA or stand 5 V across it, and not both at once — those are the same limit expressed two ways.
100 Ω is a ±10% value too
100 Ω is one of the twelve E12 values as well as one of the twenty-four E24 ones, which means it is made at ±10% and ±5% both. In practice that makes it easier to find and cheaper: E12 values are what a beginner's assortment box contains, and a shop that stocks one range stocks this value.
The nearest E12 value is 100 Ω — this one.
The same resistor as a surface-mount marking
Surface-mount resistors have no room for bands, so they carry printed digits instead — and 101 is what 100 Ω looks like on one. The scheme is the colour code with the colours replaced by the digits they stood for: two significant figures and a count of zeros.
| Marking | Used on | Reads as |
|---|---|---|
101 | Three-digit, ±5% parts | 10 followed by one zero |
1000 | Four-digit, ±1% parts | 100 with no zeros after it |
A four-digit marking is not a different system, only a more precise one: it carries three significant figures instead of two and takes one off the zero count, which is why 101 and 1000 are the same 100 Ω. If a board has both on it, the four-digit parts are the ±1% ones.
Very small ±1% parts use a third scheme, EIA-96, where two digits index a table of values and a letter gives the multiplier — 01C rather than 1002. It only covers the E96 series, so it has no marking for most of the E24 values on this site, and a marking with a letter in the middle is never one of these codes.
Where 100 Ω turns up
Hundreds of ohms is the classic LED resistor range on a 5 V rail, and the usual value for series protection on an input pin. It is the most-reached-for decade in hobby electronics after the kilohms.
Frequently asked questions
What is the colour code for a 100 Ω resistor?
brown black brown gold on a four-band resistor: brown for 1, black for 0, brown for a multiplier of ×10, and gold for ±5%.
What resistor is brown black brown gold?
100 Ω, ±5%. The first two bands are the digits 1 and 0, the third multiplies by 10, and the gold band is the tolerance.
What is the tolerance range of a 100 Ω ±5% resistor?
95 Ω to 105 Ω. A resistor measuring anywhere in that range is within specification, which is why a meter reading of 95 Ω on a 100 Ω part is not a fault.
What is the five-band code for 100 Ω?
brown black black black brown — three digit bands (1, 0, 0), then black as the multiplier and brown for ±1%. Five-band resistors carry an extra significant figure, so the third digit is the zero that a four-band code leaves to the multiplier.
Nearby values
- 110 Ω resistor colour code — brown brown brown gold
- 120 Ω resistor colour code — brown red brown gold
- 130 Ω resistor colour code — brown orange brown gold
- 150 Ω resistor colour code — brown green brown gold
- 160 Ω resistor colour code — brown blue brown gold
- 180 Ω resistor colour code — brown grey brown gold
- 200 Ω resistor colour code — red black brown gold
- 220 Ω resistor colour code — red red brown gold
- 240 Ω resistor colour code — red yellow brown gold
- 270 Ω resistor colour code — red violet brown gold