Resistor Basics 2 - Identifying Values

Resistor Value Conventions

There are several conventions for recording resistor values:

A letter is written in place of a decimal point:

  • R is written for values under 1000 for example:
    • a 820 Ohm value would be written as 820R
    • a 4.7 Ohm value would be written as 4R7
    • a 1 Ohm resistor may be written as 1R or 1R0.
    • a 0.68 Ohms may be written as R68, or 0R68
  • K would be written for resistor values in their thousands (Kilo), for example:
    • a 4700 (4.7 thousand) Ohm value would be written as 4K7,
    • a 470 000 (470 thousand) Ohm value would be written as 470K.
    • A 1000 Ohm (or 1 kilo Ohm) resistor would be written either as 1K, or 1K0.
  • M is used for higher resistor values in their millions (Mega), for example:
    • a 4 700 000 (4.7 Million) Ohm value would be written as 4M7
    • a 10 000 000 (10 million) Ohm resistor would be written as 10M
    • a 1 million Ohm resistor would be written as 1M or 1M0

NOTE: The amount of resistance above 10M is extremely small, and is rarely measured in simple electronic circuits. Many budget multimeters would show OL (Over Limit) or infinite resistance at this point.

This convention is often used in circuit diagram schematics, and occasionally printed onto the resistors themselves (especially in the case of SMD (Surface Mount Device) resistors). If you're new to electronics, you'll most likely be dealing with through-hole resistors, which have coloured stripes to identify their values.

We've already covered how to measure resistance using a multimeter in a previous section, now we look at other ways of seeing the value identified on the parts themselves:

Coloured stripes indicating resistor value

Values can be read from coloured stripes (or bands) printed onto the resistor body. Colours can be difficult to identify, especially when printed over a coloured base.

Using a multimeter can help verify values to ensure that there is no confusion over colour interpretation, but be aware of measuring bad resistors if you are unsure of the original value! When purchasing selection packs of resistors and with project kits, the values may sometimes be missing from the strips of resistors, and a multimeter can be a big help in quickly clearing up the missing values. Of course, you can spend more time calculating the values from the coloured bands for practice and use a multimeter to confirm the result.

We’ve created our colour code table for 4 and 5 band resistors, the most common through-hole resistor types. The body colour of the resistor should be ignored, as this can vary from manufacturer to manufacturer, although in our experience, the majority of blue body resistors have 5 bands, and the majority of cream resistors have 4 bands, so we’ve represented them likewise.

Ecobion Labs Resistor Color Band Value Calculator

  • You’ll need to look carefully at the resistor for a slightly larger gap at one end of the colour bands. This gap separates the Tolerance Value, and indicates which way around you should be reading the colour values. If you are unsure, note that a resistor will never have black, orange, yellow, green, blue of violet bands for tolerance values.
  • Be very careful identifying the colours, red can look orange, brown can look gold. Good lighting can make a big difference, and we highly recommend an illuminated pocket magnifier to help see the bands with better clarity.
  1. Note the values relating to the colour bands along the resistor body.
  1. Add or remove a number of zeroes after the value depending on the multiplier. If the multiplier is black, don’t do anything else.
  1. Remember, three 0’s is K or Kilo (i.e. 5 000), 6 is M or Mega (i.e. 5 000 000).

 

Common Resistor Values

Resistors are commonly available as fixed values using the IEC 60063 preferred number convention, with the same value multiplied out for different orders of magnitude. For basic electronic circuits, the E6 values would be typical (shown in bold) with the additional E24 values given in the table below:

Ecobion Labs Common Resistor values

  • When purchasing resistor selection packs, we recommend a selection that contains at least 84 different values, this will usually cover all the values above.
  • Any selection that has around 42 resistor values will be suitable for starting out, but you'll quickly find you are missing the extra resistor values. Simply go for the resistor you have that is the nearest value, and your circuit should still work. Eventually you won't be able to get away with this for more complex circuits demanding higher tolerance resistors, which will be covered in a later more advanced topic.

As the resistor tolerance improves, so does the number of values in between, giving rise to other substandards of IEC 60063.

Shorthand form of writing values

Common 3 and 4 digit resistor value codes

With SMD (Surface Mount Device) resistors, the values may be written in coded shorthand, printed into the resistor body. Like the colour table, the first digits provide the value, with the final digit providing the multiplier (there is no tolerance value).

We're including this information on identifying SMD resistors, as SMD resistors are appearing more commonly in basic electronics kits (although much more difficult to solder, but we'll save that for another day!).

The 3-Digit and 4-Digit system is used where just numbers or the letter R is included. If other letters are included, the resistor codes will probably be using the EIA-98 standard, described further below. Potentiometers often use the 3-Digit system, although the actual value may be printed instead.

Ecobion Labs SMD Resistor Value Calculator

Some SMD resistors are very small, and will need use of additional magnification, such as an illuminated pocket magnifier.

Note the first 2 digits (3 digit code) or 3 digits (4 digit code), and add a number of zeros as listed in the multiplier. if the multiplier is zero, don't add anything.

0, 000 and 0000 are all zero ohm values. Zero ohm resistors are often used as a way of bridging gaps over traces, or setting configuration options where there could be variants within the same circuit board.

Like we mentioned for the resistor colour codes, three 0’s is K or Kilo (i.e. 5 000), 6 is M or Mega (i.e. 5 000 000).

EIA-98 Standard Resistor Codes

The EIA-98 standard provides a deeper level of information, but needs use of a lookup table.

The first 2 digits provide the lookup for the value, with the third digit being the multiplier.

Ecobion Labs EIA-96 SMD Resistor Code Calculator

Other letter codes are possible, depending on the manufacturer, their product datasheets should be checked for reference.

Add a comment

Subject:
Your Name(*):
Email:
Comment(*):
Code in the picture: This is a captcha-picture. It is used to prevent mass-access by robots. (see: www.captcha.net)
 
Note: Your comment has been received and is awaiting approval
 
 


Previous page: Resistor Basics 1  Next page: Resistor Basics 3