calculator
Resistor color code calculator
Resistors carry their value as color bands. Pick the colors on your resistor and this reads the value. Type a value and it draws the resistor you're looking for. 4-band and 5-band both work.
The resistor
220 Ω ±5%
A ±5% resistor sold as 220 Ω is actually anywhere from 209 Ω to 231 Ω.
- Band 1 red = 2
- Band 2 red = 2
- Band 3 black = 0
- Digits joined: 22
- Multiplier band brown = ×10
- Value: 22 × 10 = 220 Ω
- Tolerance band gold = ±5%
How the color code works
Resistors are tiny — usually smaller than a match head — so their value is painted on as color rings instead of numbers. The rings sit near one end. Hold the resistor with the group of three (or four) rings on the left and the lonely ring — the tolerance band — on the right.
The first two or three rings are digits. Black is 0, brown is 1, red is 2, and so on up through the rainbow — orange, yellow, green, blue, violet — ending with grey (8) and white (9). The next ring is the multiplier: it tells you how many zeros to add. A 4-band resistor uses two digit rings; a 5-band one uses three, which lets it print an extra significant figure and hit values like 4.99 kΩ.
What tolerance means
The last ring says how close to the printed value the real resistor actually is. Gold is ±5%, brown is ±1%, red is ±2%. A resistor sold as "220 Ω ±5%" can be anywhere from 209 to 231 Ω. For beginner circuits (LEDs, buzzers, switches) that spread never matters. Precision analog work — filters, instrumentation, matched pairs — uses ±1% or better.
The E12 standard values
Not every number is a real resistor. Manufacturers pick 12 values per decade — 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82 — chosen so consecutive values overlap at ±10%. Every ±5% resistor you can buy is one of those numbers times 1, 10, 100, 1 000, 10 000, or 100 000. That's why every LED calculator on this site rounds up to a standard value: the exact answer often doesn't exist as a real part.
Common questions
Which end do I read from? The tolerance band is usually gold or silver and sits a little further from its neighbour than the digit bands do from each other. Put that ring on the right and read left to right.
What if I can't tell red from brown? Measure it with a multimeter on the ohms setting — it's faster and works even in bad light. Every hobby multimeter has this. Use the color code to double-check, not as the only source of truth.
My resistor has 6 bands. The sixth ring is the temperature coefficient (how much the value drifts with heat). Ignore it for hobby circuits; the first five bands still give you the value.
Try a real resistor in First Light, or use the value straight away in the LED resistor calculator. The Ohm's law skill explains what the resistance is doing in the circuit.