Resistor Color Code Calculator

Resistors are too small to print numbers on legibly, so the electronics industry settled on a code that fits on a tiny cylinder: a series of colored bands, each one carrying a piece of the resistor's value. Once you know the code, reading a resistor takes seconds — this calculator does the same lookup instantly.

How to Use the Resistor Color Code Calculator

Select the color of each of the four bands on your resistor, reading from the end closest to one edge (the tolerance band, usually gold or silver, is easiest to spot and should end up on your right). The first two bands are significant digits, the third is a multiplier, and the fourth is tolerance. The calculator returns the resistance in ohms, the tolerance percentage, and the minimum and maximum resistance the part is guaranteed to fall within.

Where This Standard Comes From

The resistor color code is formally defined in IEC 60062, the international standard for marking codes on resistors and capacitors, which is why a resistor made in one country reads identically to one made anywhere else — a genuinely global, decades-old standard that predates most of the electronics you'll ever build with it.

How the Color Code Works

Each color from black through white stands for a digit from 0 to 9: black=0, brown=1, red=2, orange=3, yellow=4, green=5, blue=6, violet=7, gray=8, white=9. The first two bands form a two-digit number, and the third band multiplies that number by a power of ten — brown means ×10, red means ×100, and so on, with gold meaning ×0.1 and silver meaning ×0.01 for resistors under 10 ohms. The calculator's default example — brown, black, red, gold — decodes to digits 1 and 0 (giving 10), multiplied by red's ×100, for a nominal resistance of 1,000 ohms, or 1 kilohm, with a gold tolerance band of ±5%.

A Worked Example: Reading a Real Resistor

Suppose you're holding a resistor with bands yellow, violet, orange, and gold. Yellow is 4, violet is 7, giving the two-digit number 47. Orange as a multiplier means ×1,000. So the resistance is 47 × 1,000, or 47,000 ohms — commonly written as 47k. With a gold ±5% tolerance, the actual value falls somewhere between 44,650 and 49,350 ohms. This exact color combination (yellow-violet-orange-gold) is one of the most common resistor values in consumer electronics, which is why "47k" often gets memorized by hobbyists just from seeing it so often.

Why Tolerance Matters

No manufacturing process is perfect, and the tolerance band tells you how far the actual resistance might drift from the printed nominal value. A 1,000-ohm resistor with a gold (±5%) tolerance band could genuinely measure anywhere from 950 to 1,050 ohms and still be considered within spec — this calculator reports both of those bounds directly. For most hobbyist projects, 5% or 10% tolerance (gold or silver bands) is perfectly fine; precision applications like audio equipment or measurement instruments often specify tighter tolerances like 1% (brown) or better.

Why 4 Bands Instead of Printed Numbers

Beyond simply fitting on a small component, color bands are readable from any rotation and don't require the resistor to be oriented a particular way under a lens — a printed number could smudge, wear off, or be too small to read reliably, while molded or painted color bands survive handling and stay legible for the life of the component. Some precision resistors use a 5-band code instead, adding a third significant digit for finer resolution, but the 4-band code covers the overwhelming majority of resistors found in general electronics.