Hong Life CalculatorsUnderstanding the resistor color code calculator — concept and principle
Small through-hole resistors are too small to print their value, so it is coded in colored bands. This calculator decodes 4-band and 5-band resistors into a resistance value, its tolerance and the range the true value can fall in. It is used when sorting parts, checking a board during repair and confirming you picked the right component before soldering.
How it is calculated
- 4-band: R = (10·d₁ + d₂) × 10^m
- 5-band: R = (100·d₁ + 10·d₂ + d₃) × 10^m
- Range: R × (1 − t/100) to R × (1 + t/100)
The digit colors are black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8, white 9. The multiplier band uses the same colors as a power of ten, plus gold (×0.1) and silver (×0.01). Tolerance colors: brown ±1%, red ±2%, green ±0.5%, blue ±0.25%, violet ±0.1%, gold ±5%, silver ±10%. Choose "— (4-band)" for band 3 when the resistor has only two digit bands.
The principle
The scheme is standardized internationally in IEC 60062. The digit bands give the significant figures and the multiplier gives the power of ten, exactly like scientific notation: brown-black-red means 1, 0 and ×10², or 1.0 × 10³ Ω. Three significant figures in 5-band codes are needed for precision resistors (typically ±1% or better) whose values come from finer series such as E96. Tolerance describes the permitted manufacturing deviation from the marked value, not drift during use.
Worked example
- Inputs: brown, black, (no third digit), red multiplier, gold tolerance.
- Digits: brown = 1, black = 0, so 10.
- Multiplier: red = 10², so 10 × 100 = 1,000 Ω = 1 kΩ.
- Tolerance: gold = ±5%.
- Range: 1,000 × 0.95 = 950 Ω to 1,000 × 1.05 = 1,050 Ω, shown as 950 Ω – 1.05 kΩ.
How to read the result
A ±5% part can legitimately measure anywhere in the range, so a reading of 980 Ω on a 1 kΩ gold-band resistor is normal. If your multimeter shows a value outside the range, the resistor may be damaged, or the reading may be affected by other components on the board; measure with at least one leg lifted.
Common mistakes
- Reading from the wrong end. The tolerance band is usually separated by a gap and often gold or silver, which never appears as the first band.
- Confusing brown with red or orange, or violet with blue, under poor light.
- Treating the third band of a 5-band resistor as the multiplier.
- Ignoring a sixth band, which indicates the temperature coefficient.
Frequently asked questions
What does a resistor with a single black band mean?
It is a zero-ohm link, used as a jumper on circuit boards.
Why are resistor values like 4.7, 22 and 68 so common?
They come from the E-series of preferred numbers (IEC 60063), spaced so that neighbouring values overlap within their tolerance.
How do I tell which end to start from?
The first band is usually closer to one end, and the tolerance band is set apart with a wider gap.
Sources: IEC 60062, Marking codes for resistors and capacitors · IEC 60063, Preferred number series for resistors and capacitors