Decodes a standard 4-band resistor color code into its resistance value and tolerance.
How it works
The first two bands give the significant digits, the third band gives the multiplier, and the fourth band gives the tolerance — all read from the standard color-to-value table.
What this does not include
This covers the common 4-band format — 5-band and 6-band resistors (which add a third significant digit or a temperature coefficient) use a related but different color mapping this calculator doesn’t include.
How to use this calculator
- Select each band’s color, reading from the resistor’s body outward.
A worked example
Bands brown-black-red-gold: resistance = 1 kΩ, tolerance = ±5%.
Bands yellow-violet-orange-gold: resistance = 47 kΩ, tolerance = ±5%.
What the variables mean
| Variable | Meaning |
|---|---|
| Band 1, Band 2 | The first two significant digits |
| Band 3 | Multiplier — how many zeros to append |
| Band 4 | Tolerance band, indicating manufacturing precision |
Edge cases worth knowing
Each color maps to a fixed digit, not an arbitrary label — black is always 0, brown always 1, and so on, following a standardized color code used across the electronics industry.
An invalid color name has no defined digit, so the calculator declines to show a result — the color bands must match the standard resistor color code exactly.
Frequently asked questions
Why do resistors use color codes instead of printed numbers?
Colors remain readable regardless of the resistor’s orientation and are cheaper to print reliably on small components than text.
How do I know which end to start reading from?
The tolerance band (often gold or silver) is typically set apart with a wider gap, marking it as the last band — read the others from the opposite end.
What does the tolerance band actually mean?
It states how far the resistor’s actual resistance may vary from its labeled value — a 5% tolerance resistor labeled 1,000 Ω could measure anywhere from 950 to 1,050 Ω.
