Through-hole resistors print their value as coloured bands. This calculator decodes the common 4-band scheme: pick each band’s colour and read the resistance in ohms (or kΩ / MΩ) with its tolerance — handy for electronics hobbyists, students, and anyone repairing a board.
How it works
In a 4-band resistor the first two bands are significant digits, the third is a multiplier (a power of ten), and the fourth is the tolerance. The colours map to numbers in a fixed sequence (black 0 through white 9). The resistance is:
(digit1 × 10 + digit2) × 10^multiplier
Gold and silver are special multipliers (×0.1 and ×0.01) and tolerance values (±5% and ±10%). The tool combines your band selections with this mapping and formats the value in the cleanest unit.
Example
Bands brown, black, red, gold:
- Brown = 1, black = 0 → significant digits 10
- Red multiplier = ×10² = ×100
- 10 × 100 = 1,000 Ω = 1 kΩ
- Gold tolerance = ±5%
| Colour | Digit | Multiplier |
|---|---|---|
| Black | 0 | ×1 |
| Brown | 1 | ×10 |
| Red | 2 | ×100 |
| Orange | 3 | ×1k |
| Yellow | 4 | ×10k |
| Green | 5 | ×100k |
| Blue | 6 | ×1M |
| Violet | 7 | ×10M |
| Gold | – | ×0.1 (±5%) |
| Silver | – | ×0.01 (±10%) |
Which direction do I read the bands?
This trips up beginners more than the colour chart does. The tolerance band — usually gold or silver — is almost always on the right side, and it is often separated from the first three bands by a slightly larger gap. Hold the resistor so the tolerance band is on the right, then read left to right: digit, digit, multiplier, tolerance.
If a resistor has no obvious gold or silver band, it is likely ±20% with no tolerance band shown, or it may be a 5-band resistor (three digits, a multiplier, and a tolerance). The 5-band scheme is common on precision resistors with 1% or 0.5% tolerance.
Practical notes for circuit work
Tolerance matters more than beginners expect. A ±5% (gold) resistor nominally rated 10 kΩ could measure anywhere from 9,500 Ω to 10,500 Ω. For LED current-limiting or voltage dividers this is usually fine; for precision timing or filtering circuits, use ±1% (brown) or better.
The E-series explains why you find resistors in values like 10, 12, 15, 18, 22, 27 rather than arbitrary numbers. The E12 series has 12 values per decade, each spaced so even the worst-tolerance resistors in adjacent values do not overlap. Most component kits ship with E12 or E24 values.
Reading faded bands: if a band looks ambiguous between orange and red, measure the resistor with a multimeter rather than guessing. The decoder gives you the expected value so you know what to expect before you probe.
All decoding happens locally in your browser; nothing is sent anywhere.