Resistors are the most used part in electronic circuits, but they are so small that it is hard to print the value as a number. So color bands are wrapped around the body to show the value. Once you learn to read the bands, you will use that skill for life, and if you understand value, tolerance, power rating, and the standard series (E12 and E24), you will not flounder when choosing parts. This article covers reading color bands along with the basics you need to choose a resistor. If you want to calculate right away, use the resistor color code calculator.
How to read the color bands
The colors correspond to digits as follows: black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8, white 9. For the full table, see the table on the calculator page.
- Put the side with the tolerance band (gold, silver, and so on) on the right.
- From the left, read the 2 digit bands (4-band) or 3 digit bands (5-band) as digits and join them.
- The next band is the multiplier. It means how many zeros to add after the digits (a power of 10).
- The last band is the tolerance. Gold is ±5%, silver is ±10%, and brown is ±1%.
For example, yellow-violet-red-gold is 4 and 7 with a multiplier of ×100, so 4,700 Ω = 4.7 kΩ, with a tolerance of ±5%.
What tolerance means
Tolerance shows how far the actual resistance may deviate from the marked value. A ±5% 1 kΩ resistor can be anywhere from 950 to 1,050 Ω. ±5% is enough for most LED resistors and pull-up resistors. If you are making a reference voltage with a divider or need accurate timing, use ±1% metal film resistors.
E series: why the values are spaced apart
Resistors are not sold in just any value; only set standard values are made. The E series places the values in a geometric sequence so that, allowing for tolerance, they do not overlap.
| Series | Tolerance | Values per decade (×10) | Use |
|---|---|---|---|
| E12 | ±10% | 12 | Starter sets, general circuits |
| E24 | ±5% | 24 | The most common carbon and metal film resistors |
| E96 | ±1% | 96 | Precision circuits, reference voltages |
The base values of E12 are 1.0, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, and 8.2, multiplied by 10, 100, 1k, 10k…. E24 adds 1.1, 1.3, 1.6, 2.0, 2.4, 3.0, 3.6, 4.3, 5.1, 6.2, 7.5, and 9.1 to those. If the resistance you calculated is not among the standard values, picking a nearby value is fine in most cases, and if you need it exact, combine two resistors with the series & parallel resistor calculator.
Power rating
When current flows through a resistor, it gets hot. The power dissipation is P = V × I = I² × R, and a resistor must be used within its rating (1/8 W, 1/4 W, 1/2 W, 1 W, and so on). A typical 1/4 W resistor has a body about 6 mm long.
- 1/4 W is enough for pull-ups and pull-downs in signal circuits and for LED resistors (tens of mW).
- Using half the rating or less keeps it long-lived and from getting hot.
- Where the power is large, use a 1/2 W to several-watt resistor, or several in parallel to share the heat.
Types of resistors
- Carbon film: cheap and common. ±5% tolerance, suited for beginners.
- Metal film: ±1% tolerance with less drift and noise, used in precision circuits. Often 5-band.
- Wire-wound: for large power, with a big ceramic body that gets hot.
- Chip resistor (SMD): for surface mounting, using a numeric code. 103 is 10 × 10³ = 10 kΩ, and 4R7 is 4.7 Ω.
Commonly used values
| Use | Value |
|---|---|
| LED resistor on 5 V (about 10 mA) | 330 Ω |
| Digital input pull-up and pull-down | 4.7 kΩ – 10 kΩ |
| Transistor base resistor | 1 kΩ – 10 kΩ |
| Divider reference | two 10 kΩ |
| 555 timer R1, R2 | 1 kΩ – 100 kΩ |
A habit of checking
When the colors look alike and are hard to read, check with the multimeter's resistance mode. If it is already soldered into a circuit, other parts affect the reading, so lift one leg of the resistor before measuring to be accurate. Storing parts in value-labeled bags or a compartment box so they do not get mixed up is also a good habit (see the starter parts kit guide).
Summary
Read the color bands in the order "two digits + multiplier + tolerance", and the start is putting the tolerance band on the right. Knowing the standard values (E12 and E24) and the power rating reduces trial and error when you choose resistors. Next, continue with LED Current-Limiting Resistors and Brightness Control, which uses this resistor together with an LED.