Resistor Color Code Calculator
Resistor Color Code Calculator
Resistor color codes are a standardized system for marking resistance values and tolerances on small resistors using colored bands. Learning to read them is a fundamental skill in electronics.
Conversion Formula
For 4-band resistors: value = (band1 × 10 + band2) × multiplier. For 5-band: value = (band1 × 100 + band2 × 10 + band3) × multiplier. The final band gives the tolerance percentage.
Step-by-Step Examples
4-band: Brown, Black, Red, Gold = 1000 Ohm +/- 5%
(1×10 + 0) × 100 = 1000 ohms, Gold = 5% tolerance
4-band: Yellow, Violet, Orange, Gold = 47 kOhm +/- 5%
(4×10 + 7) × 1000 = 47000 ohms = 47k
5-band: Red, Red, Black, Brown, Brown = 2200 Ohm +/- 1%
(2×100 + 2×10 + 0) × 10 = 2200 ohms, Brown = 1%
History
The resistor color code was developed in the 1920s by the Radio Manufacturers Association (now the Electronic Industries Alliance). It was standardized as RMA Standard RMA/EIA-RS-279 and later adopted by IEC as part of IEC 60062.
Common Use Cases
- Identifying resistors from a parts bin
- Circuit board repair and reverse engineering
- Electronics prototyping
- Educational lab work
- Quality control inspection
Frequently Asked Questions
How do I read a resistor color code?
Hold the resistor with the tolerance band (usually gold or silver) on the right. Read the color bands left to right. For a 4-band resistor: bands 1 and 2 are digits, band 3 is the multiplier, band 4 is tolerance. For 5-band: bands 1-3 are digits, band 4 is multiplier, band 5 is tolerance.
Which direction do I read the bands?
Read from left to right, with the tolerance band (gold or silver) on the right end. If both ends look the same, the first band is usually closer to one lead. Higher-precision (5-band) resistors have a wider gap before the tolerance band.
Why do resistors use color codes instead of numbers?
Color codes were introduced in the 1920s because resistors were too small to print readable numbers on. Even though printing technology has improved, the color code system remains widely used and universally understood by electronics technicians worldwide.
What does a 5-band resistor mean?
A 5-band resistor has a third significant digit, giving it greater precision. Standard 4-band resistors specify values to two significant figures (e.g., 4700 ohms), while 5-band resistors specify three (e.g., 4700 ohms can be specified as 4.70k, distinguishing it from 4.7k).