Resistor Calculator

A resistor is one of the most common parts in electronics. It limits the flow of current, and its value is measured in ohms. Most resistors are too small to print a number on, so their value is shown with colored bands. The Resistor Color Code Calculator reads these bands for you. It also works the other way round, and shows the bands for a value that you need.

What you enter

• The number of bands: 4, 5 or 6.
• The color of each band, from the end of the resistor where the bands are closest together.
• Or, to go the other way: a resistance, the number of bands and the tolerance that you want.

The color code

Color	Digit	Multiplier	Tolerance	Temperature coefficient
Black	0	x 1		250 ppm/K
Brown	1	x 10	±1%	100 ppm/K
Red	2	x 100	±2%	50 ppm/K
Orange	3	x 1,000 (1 k)		15 ppm/K
Yellow	4	x 10,000 (10 k)		25 ppm/K
Green	5	x 100,000 (100 k)	±0.5%
Blue	6	x 1,000,000 (1 M)	±0.25%	10 ppm/K
Violet	7	x 10,000,000 (10 M)	±0.1%	5 ppm/K
Gray	8	x 100,000,000 (100 M)	±0.05%	1 ppm/K
White	9	x 1,000,000,000 (1 G)
Gold		x 0.1	±5%
Silver		x 0.01	±10%

To remember the order of the ten digit colors, from 0 to 9: Black, Brown, Red, Orange, Yellow, Green, Blue, Violet, Gray, White. A helpful phrase is "Better Be Right Or Your Great Big Venture Goes West".

Chart: the digits

Each color is drawn as a bar that gets longer as the digit grows. The bar for 0 has three blocks, and each digit adds three more.

0 Black   ███ 0
1 Brown   ██████ 1
2 Red     █████████ 2
3 Orange  ████████████ 3
4 Yellow  ███████████████ 4
5 Green   ██████████████████ 5
6 Blue    █████████████████████ 6
7 Violet  ████████████████████████ 7
8 Gray    ███████████████████████████ 8
9 White   ██████████████████████████████ 9

How to read the bands

4 bands: the first two are digits, the third is the multiplier, and the fourth is the tolerance.

value = (digit 1 and digit 2 as a number) x multiplier

5 bands: the first three are digits, the fourth is the multiplier, and the fifth is the tolerance. This is used for resistors that are more exact.

value = (digit 1, digit 2 and digit 3 as a number) x multiplier

6 bands: the same as 5 bands, and the sixth band gives the temperature coefficient. It says how much the value changes when the temperature changes, in parts per million for each kelvin.

Which end do you start from? The tolerance band is often gold or silver, and it is separated a little from the other bands. Hold the resistor with that band on the right, and read from the left. If the resistor has no gold or silver band, the first band is the one that is closest to an end.

Worked examples

• Bands: Brown, Black, Red, Gold (4 bands)
  Calculation: 10 x 100, ±5%
  Value: 1 kΩ ±5%
• Bands: Yellow, Violet, Orange, Gold
  Calculation: 47 x 1,000, ±5%
  Value: 47 kΩ ±5%
• Bands: Red, Red, Brown, Silver
  Calculation: 22 x 10, ±10%
  Value: 220 Ω ±10%
• Bands: Brown, Black, Black, Brown, Brown (5 bands)
  Calculation: 100 x 10, ±1%
  Value: 1 kΩ ±1%
• Bands: Red, Red, Black, Orange, Red, Red (6 bands)
  Calculation: 220 x 1,000, ±2%, 50 ppm/K
  Value: 220 kΩ ±2%
• Bands: Brown, Black, Gold, Gold
  Calculation: 10 x 0.1, ±5%
  Value: 1 Ω ±5%
• Bands: Yellow, Violet, Silver, Gold
  Calculation: 47 x 0.01, ±5%
  Value: 0.47 Ω ±5%

What the tolerance means

No resistor is exactly the value that is marked. The tolerance is how far the real value can be from it. A 1 kΩ resistor with a tolerance of 5% can be anywhere from 950 Ω to 1,050 Ω. The calculator shows this range.

Tolerance	Color	A 1 kΩ resistor is between
±10%	Silver	900 Ω and 1.1 kΩ
±5%	Gold	950 Ω and 1.05 kΩ
±2%	Red	980 Ω and 1.02 kΩ
±1%	Brown	990 Ω and 1.01 kΩ
±0.5%	Green	995 Ω and 1.005 kΩ

The colored bars below show the tolerance of each color. Each block is a quarter of one percent:

Gray    ±0.05%  █
Violet  ±0.1%   █
Blue    ±0.25%  █
Green   ±0.5%   ██
Brown   ±1%     ████
Red     ±2%     ████████
Gold    ±5%     ████████████████████
Silver  ±10%    ████████████████████████████████████████

A resistor with only four bands and no tolerance band has a tolerance of ±20%. The calculator does not use this old marking.

Standard values

You will not find every value in the shops. Resistors are made in standard series. The E24 series, used for 5% resistors, has 24 values for each power of ten:

10  11  12  13  15  16  18  20  22  24  27  30
33  36  39  43  47  51  56  62  68  75  82  91

These values are chosen so that the tolerance ranges of neighbours nearly touch. For 1% resistors there is a series of 96 values, called E96, and they are usually marked with 5 bands. When you enter a value in the calculator, it tells you whether it is a common E24 value. If you need 4.99 kΩ, you need a 1% resistor with 5 bands. With 4 bands, the nearest value is 5 kΩ.

Tips

• Check with a meter. The colors can look different in poor light, and brown, red and orange are easy to mix up. A multimeter gives the real value.
• Measure a resistor when it is out of the circuit. Other parts can change the reading.
• Pick a value in the right series. Use E24 for 5% and E96 for 1%.
• Check the power rating. The bands do not show it. It depends on the size of the resistor, and 1/4 watt is common.

What this calculator does not include

• The power rating of a resistor, and its maximum voltage.
• Surface-mount resistors, which are marked with numbers, and not with colors.
• Old markings, such as a 4-band resistor with no tolerance band.

This tool gives a general guide only. For a circuit that matters, check the value with a meter and follow the data sheet of the part.