1.8 Ω resistor colour code
browngreygoldgold
1.8 Ω ±5%
brown grey gold gold — four bands, read from the end with the bands closest to it.
| Band 1 — first digit | brown = 1 |
| Band 2 — second digit | grey = 8 |
| Band 3 — multiplier | gold ÷ 10 |
| Band 4 — tolerance | gold ± 5% |
| Value | 1.8 Ω |
| Acceptable range | 1.71 Ω to 1.89 Ω |
Reading it
The two digit bands give 18 and the multiplier band divides it by 10:
18 ÷ 10 = 1.8 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 1.8 Ω ±5% resistor is in specification anywhere from 1.71 Ω to 1.89 Ω. A meter reading of 1.71 Ω on this part is not a fault and not a reason to replace it.
1.8 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 1.8 Ω reads
browngreyblacksilverbrown
— brown grey black silver brown. The digits become 1, 8 and 0, and the multiplier drops one decade to silver to compensate. The brown final band is ±1% rather than ±5%, which narrows the range to 1.78 Ω–1.82 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 1.8 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 | 263.5 mA | 0.5 V |
| ¼ W | 372.7 mA | 0.7 V |
| ½ W | 527 mA | 0.9 V |
| 1 W | 745.4 mA | 1.3 V |
The quarter-watt part is the one in everybody's drawer: at 1.8 Ω it will carry 372.7 mA or stand 0.7 V across it, and not both at once — those are the same limit expressed two ways.
1.8 Ω is a ±10% value too
1.8 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 1.8 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 1R8 is what 1.8 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 |
|---|---|---|
1R8 | Three-digit, ±5% parts | 1.8 Ω — the R is the decimal point |
1R80 | Four-digit, ±1% parts | 1.80 Ω — the R is the decimal point |
Below ten ohms there are not two digits to work with before the decimal point, so an R marks the decimal place: 1.8 Ω is printed 1R8. The R is doing the job the multiplier band does on a through-hole part, and a marking with an R in it is always a low value — never a large one.
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 1.8 Ω turns up
Values in single-figure ohms are current-sense and snubber territory. A resistor this small is not there to limit anything much — it is there to be measured across, to damp a ringing edge, or to sit in series with a supply as a crude fuse. At these values the resistance of the leads and the solder joints is a measurable fraction of the part, which is why current-sense designs use four-terminal parts rather than a colour-coded one.
Frequently asked questions
What is the colour code for a 1.8 Ω resistor?
brown grey gold gold on a four-band resistor: brown for 1, grey for 8, gold for a multiplier of ÷10, and gold for ±5%.
What resistor is brown grey gold gold?
1.8 Ω, ±5%. The first two bands are the digits 1 and 8, the third multiplies by 0.1, and the gold band is the tolerance.
What is the tolerance range of a 1.8 Ω ±5% resistor?
1.71 Ω to 1.89 Ω. A resistor measuring anywhere in that range is within specification, which is why a meter reading of 1.71 Ω on a 1.8 Ω part is not a fault.
What is the five-band code for 1.8 Ω?
brown grey black silver brown — three digit bands (1, 8, 0), then silver 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
- 2 Ω resistor colour code — red black gold gold
- 2.2 Ω resistor colour code — red red gold gold
- 2.4 Ω resistor colour code — red yellow gold gold
- 2.7 Ω resistor colour code — red violet gold gold
- 3 Ω resistor colour code — orange black gold gold
- 3.3 Ω resistor colour code — orange orange gold gold
- 3.6 Ω resistor colour code — orange blue gold gold
- 3.9 Ω resistor colour code — orange white gold gold
- 4.3 Ω resistor colour code — yellow orange gold gold
- 4.7 Ω resistor colour code — yellow violet gold gold