Marking of nominal resistance value

Chip type fixed resistors are marked in 3 or 4 characters depending on the product type and size. Leaded types on the other hand, are marked with color codes.
These codes refer to the resistance value (and tolerance) and are expressed as significant digits rather than directly indicating the resistance value.

Significant digits

Resistance values in the lineup are not rounded integer values, but rather odd values such as 2.2 Ω and 4.7 Ω. This is because resistance value is defined by E series, that divides the interval from 1 to 10 into geometric series. E12 series and E24 series are generally used but some resistors with the tolerance under 1% take E96 series and E192 series. The passive components including resistors use this standard value as significant digits and represent constants.

E represents "Exponent". E12 series, for example, divides 1 to 10 into geometric series, that is twelfth root of ten. Since it is a geometric series, the values are in equal intervals on logarithmic scale. Even though odd numbers may be confusing at first, they come in handy when adjusting the resistance value by certain amount of percentage in designing stages.

Generally, there is a relationship between the resistance tolerance and the nominal resistance value. There are more choices for resistance values such as E6 at ± 10%, E12 or E24 at ± 5%, E96 at ± 1% or ± 0.5%, E192 at below ± 0.5%.

Indication of resistance tolerance

The symbols used for the resistance tolerance are shown in the table below.

Indication of resistance value (and tolerance)

Case of flat chip resistors

・3-digit marking
The first two digits indicate the significant digits of resistance value for E3, E6, E12 and E24. And the last digit indicates a power of ten by which to multiply the given resistor value (multiplier, 10ⁿ.)
R represents a decimal point; L represents a decimal point for resistance value in mΩ; U represents a decimal point for resistance value in µΩ.

153 : 15× 10³ =15000=15kΩ
1R5 : 1.5Ω
1L5 : 1.5mΩ
50U :  50μΩ                               
                     

[15] Significant digits, [3] Multiplier(10³)
[15] Significant digits, [R] Decimal point
[15] Significant digits, [L] mΩ
[50] Significant digits, [U] μΩ

・4-digit marking
The first three digits indicate the significant digits of resistance value, and the last digit indicates a multiplier, 10ⁿ.

Case of leaded type resistors and MELF type chip resistors

Resistance and tolerance value of leaded type resistors are generally marked in color codes. Colors corresponding to numbers and resistance tolerances are shown in the table below.

・4-band marking
The first two bands indicate the significant digits of the nominal resistance value, and the third band indicates a multiplier. The last band indicates the resistance tolerance.

e.g.）Red / Red / Orange / Gold：22×10³Ω±5％→ 22kΩ±5％

・5-band marking
The first three bands indicates significant digits of nominal resistance, the 4th band indicates a multiplier, and the last band indicates the resistance tolerance.

e.g.）Yellow / Purple / Green / Red / Brown：475×10²Ω±1％ → 47.5kΩ±1％

The first band can be distinguished from the last band by identifying the one that is closer to the lead wire. For 5-band types, the space between the 4th and 5th bands is a little wider than the others.
Bands that indicate the multiplier are sometimes slightly thicker than the others.

Product size indication of flat chip resistors

The size of chip resistors are indicated in three different ways; symbolic, numeric in milli-meter and numeric in inch.
Symbolic codes with a combination of a number and a alphabet such as 1J and 2A were originally used to indicate the power ratings (1J: 1/16W, 1/10W: 2A, 1/8W: 2B, 1/4W: 2E...) This is because when flat chip resistors were developed initially, the power rating also suggested the product size. Even though KOA has improved the power rating of each product size, these size code such as 1J or 2A is still used as a size code since it is a well recognized method.

Numeric codes are expressed in millimeter or inch, both of which are represented by 4 numbers (5 numbers in exceptional cases).

In millimeter size, AABB indicates a length of A.A mm and width of B.B mm with a electrode arranged vertically.
  So the in example of 1608, this indicates L = 1.6mm× W = 0.8mm

In inch size, CCDD indicates a length of 0.CC inch and a width of 0.DD inch with a electrode arranged vertically.

  So in the example of 0603, this indicates L = 0.06 inch × W= 0.03 inch

Since the metric system is more widely used in Japan, KOA lists 4-digit numeric codes in millimeter in the parentheses next to the symbolic code such as 1J and 2A on the catalog.

Following is the code chart for the three different indications.