Every through-hole resistor in electronics is colour-coded with a series of painted bands that encode its resistance value and tolerance.
About this calculator
Every through-hole resistor in electronics is colour-coded with a series of painted bands that encode its resistance value and tolerance. The colour code is one of the oldest standardised systems in electronics, dating to before World War II, and remains universal today. Once you can read the bands fluently, you can identify any resistor on a workbench, in a kit or on a PCB without a multimeter.
The code uses three pieces of information. The first 2 (or 3, for precision resistors) bands are the significant digits of the resistance, with each colour mapped to a digit 0-9. The next band is the multiplier -- a power of 10 used to scale the digits up or down. The final separate band, often gold or silver, gives the manufacturing tolerance as a percentage. A 4-band resistor is the most common, with 2 digits + multiplier + tolerance. A 5-band precision resistor has 3 digits + multiplier + tolerance, giving an extra significant figure for tighter accuracy.
For example, a resistor with bands yellow, violet, red, gold reads 4-7-×100-±5%, giving 4700 Ω or 4.7 kΩ ± 5%. With ±5% tolerance, the actual resistance can be anywhere from 4465 Ω to 4935 Ω. For analog filters, audio circuits, and instrumentation amplifiers, you'd choose a precision 5-band resistor with 1% or even 0.1% tolerance, recognised by brown or violet tolerance bands. Combine this calculator with the [[voltage-divider]] calculator to size resistor pairs for output voltages, and the [[paint]] calculator and others in the everyday section for non-electronic projects.
Common uses
- Identifying resistor values on a hobbyist breadboard or PCB without a multimeter
- Quick reference during DIY Arduino, Raspberry Pi and ESP32 builds
- Teaching electronics fundamentals -- decoding the colour code is a Day 1 lesson
- Sorting and labelling bulk resistor kits when packaging gets jumbled
- Verifying purchased resistors match the design specification before assembly
Frequently asked questions
What does the gold band on the multiplier mean?
Gold as a multiplier means × 0.1, used for sub-ohm resistors. For example, brown-black-gold = 1.0 Ω. Silver as multiplier means × 0.01, even smaller. Gold and silver as tolerance bands mean ±5% and ±10% respectively.
How do I know which side to start reading from?
The tolerance band is usually gold, silver or wider than the others, and is placed slightly apart from the digit bands. Hold the resistor with the tolerance band on the right, then read the digit bands from left to right.
Why are some resistors 4-band and some 5-band?
4-band is the standard for general-purpose resistors with ±5% or ±10% tolerance. 5-band is used for precision resistors (typically ±1% or better) where an extra significant digit is needed. Some 6-band resistors also include a temperature coefficient as the sixth band.
Can I check the value with a multimeter?
Yes -- always verify critical resistors with a multimeter before assembly, especially in feedback loops, current-limiting applications or anywhere the wrong value could damage components. The colour code can wear or fade on old resistors.
What about SMD (surface mount) resistors?
SMD resistors don