Resistor Colour Code Calculator
Resistors are too small to print numbers on, so their value is encoded in coloured bands. This calculator decodes them, and works in reverse when you need to find the right part.
Formula
Resistance = (digit bands as a number) × 10^multiplier
- Four bands: two digits, a multiplier and a tolerance
- Five bands: three digits, a multiplier and a tolerance
Brown-black-red-gold: 1, 0, ×100, ±5% = 1,000 Ω ±5%
How the Bands Work
On a four-band resistor: the first two bands are digits, the third is a multiplier, and the fourth is tolerance.
The digit values run black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8, white 9.
Brown-black-red-gold is 1, 0, ×100 = 1,000 Ω (1 kΩ) at ±5%.
Five-band resistors add a third digit for precision parts; six-band versions add a temperature coefficient.
Reading It the Right Way Round
Start from the end with bands grouped closest together, and keep the tolerance band on the right. Gold and silver only ever appear as tolerance or multiplier bands, so if you see one it belongs at the far end.
Read a resistor backwards and brown-black-red becomes red-black-brown — 200 Ω rather than 1 kΩ, a factor of five out.
Tolerance and E-Series Values
Tolerance tells you how far the real value may sit from the nominal: gold is ±5%, brown ±1%, red ±2%.
Resistors come in standard E-series values rather than every number, which is why 345 Ω does not exist off the shelf and you round up to 360 Ω. Always confirm a decoded value with a multimeter when it matters — colours fade, and on some bodies red and orange are hard to tell apart.
Quick Reference
| Colour | Digit | Multiplier | Tolerance |
|---|---|---|---|
| Black | 0 | ×1 | — |
| Brown | 1 | ×10 | ±1% |
| Red | 2 | ×100 | ±2% |
| Orange | 3 | ×1k | — |
| Yellow | 4 | ×10k | — |
| Green | 5 | ×100k | ±0.5% |
| Blue | 6 | ×1M | ±0.25% |
| Violet | 7 | ×10M | ±0.1% |
| Grey | 8 | — | ±0.05% |
| White | 9 | — | — |
| Gold | — | ×0.1 | ±5% |
| Silver | — | ×0.01 | ±10% |
Frequently Asked Questions
- How do I read a resistor colour code?
- First two bands are digits, third is the multiplier, fourth is tolerance. Brown-black-red-gold is 10 × 100 = 1,000 Ω at ±5 per cent.
- Which end do I start from?
- The end where the bands are grouped most closely, keeping the tolerance band on the right. Gold or silver bands are always tolerance or multiplier, never the first digit.
- What do 5 and 6-band resistors mean?
- Five bands add a third significant digit for precision parts. Six bands add a temperature coefficient showing how resistance drifts with heat.
- Why can I not find the exact value I calculated?
- Resistors are made in standard E-series values. Round up to the nearest available value, which slightly lowers the current and is the safe direction.