Resistor colour code
Decode a 4-band or 5-band resistor into a resistance and tolerance window, and see the nearest E24 value you can actually buy. The band contributions are listed individually so a misread colour is easy to spot.
| Band | Colour | Contribution |
|---|---|---|
| Band 1 | Brown · 1 | First significant digit |
| Band 2 | Black · 0 | Second significant digit |
| Multiplier | Red · 2 | × 10^2 |
| Tolerance | Brown · ±1% | ± on the nominal value |
| Result | 1.000 kΩ | 990.000 Ω to 1.010 kΩ |
Five-band resistors carry three significant digits, which is how 1% values such as 4.99 kΩ are marked.
R = (10d₁ + d₂)·10^m · two significant digits
R = (100d₁ + 10d₂ + d₃)·10^m · three significant digits
R ± R·t/100 · the fourth or fifth band
digit → digit → multiplier → tolerance · the tolerance band is spaced slightly apart
A clear path from inputs to results.
Resistor colour bands encode two or three significant digits, a multiplier and a tolerance. This decoder turns the bands into a value, shows the tolerance window, and identifies the nearest E24 preferred number — because the value you read is rarely the value in the parts drawer.
How to use
- Count the bands: four for 5% and 10% parts, five for 1% and better.
- Read from the end opposite the tolerance band, which is spaced slightly apart.
- Select the colour of each band in order.
- Read the nominal resistance and the tolerance window.
- Check the nearest E24 value — that is what the manufacturer actually stocks.
- Remember that in-circuit measurement is unreliable: parallel paths change the reading.
The formula
Reference: IEC 60062, "Marking codes for resistors and capacitors".
Worked example
Brown, black, red, gold (default inputs)
- 4-band resistor.
- Band 1 brown (1), band 2 black (0).
- Multiplier red (×100).
- Tolerance gold (±5%).
- 1
Significant digits: 10.
- 2
Multiply by 100: 10 × 100 = 1,000 Ω.
- 3
Tolerance ±5% is ±50 Ω.
- 4
The window is 950 Ω to 1,050 Ω.
1 kΩ ±5%, a window of 950 Ω to 1,050 Ω. Nearest E24 value is 1 kΩ.
Interpreting the result
The tolerance band is the part that matters in design. A 1 kΩ ±5% part is guaranteed only to sit between 950 Ω and 1,050 Ω, which is a 100 Ω spread. If a circuit is sensitive to a 5% shift, a 1% metal-film part is the fix, not a tighter calculation. Five-band parts exist precisely because 1% tolerances need a third significant digit.
Assumptions & limitations
- Bands are read in the standard order, away from the tolerance band.
- Colours are correctly identified. Brown versus red and violet versus blue are the usual errors under warm light.
- The resistor is at its rated value; self-heating shifts it by the temperature coefficient, which is not encoded in the bands.
- Gold and silver multipliers (×0.1 and ×0.01) are supported; they are rare outside low-value parts.
- The nearest E24 value assumes the standard 5% series; E96 is the 1% series.
Frequently asked questions
Which end do I read from?
Start at the end opposite the tolerance band. The tolerance band is usually gold or silver and is separated by a slightly wider gap. If all bands look evenly spaced, measure with a meter rather than guessing.
What does the gold band mean?
As a multiplier it means ×0.1; as a tolerance it means ±5%. Position determines which. Gold in the multiplier position gives values below 10 Ω.
What is the E24 series?
A set of 24 preferred values per decade, spaced so that adjacent values differ by roughly the tolerance. It is why you can buy 4.7 kΩ but not 4.8 kΩ.
Why is there no green or blue in my 4-band reading?
Green and blue are valid digits (5 and 6) and valid tolerance bands (±0.5% and ±0.25%). Their presence usually means the part is a 5-band precision resistor, so switch the band count.
Why does my meter read differently from the bands?
In-circuit measurement includes parallel paths, and your fingers add resistance. Lift one leg to measure. Meter lead resistance also matters below about 10 Ω.
Are 6-band resistors different?
They add a temperature-coefficient band. The first five bands work exactly as in the 5-band case; the sixth gives ppm/K.
Methodology last reviewed 2026-10-18. Results are informational and not financial or engineering advice — see our disclaimer.