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SMD Resistor Code Calculator

Surface-mount resistors are too small for colour bands, so the value is printed as a short code. For a 3-digit code the last digit is the number of zeros: 103 means 10 followed by three zeros, which is 10 kΩ. This calculator also reads 4-digit codes, R notation (4R7) and EIA-96 codes (01A).

Result

Resistance of 103

10 kΩ

Kind of code: 3-digit code
How it reads: 10 × 1000 (the last digit, 3, is the number of zeros to add)
Usual tolerance: Usually ±5 % (sometimes ±1 %)

The formula

A 3-digit or 4-digit code

\htmlData{sym=R}{R} = \htmlData{sym=N:code}{N} \times 10^{\htmlData{sym=K:last}{K}}

An EIA-96 code: the table value times the letter’s multiplier

\htmlData{sym=R}{R} = \htmlData{sym=N:table}{N} \times \htmlData{sym=M:letter}{M}

What each letter means

$R$: Resistance (Ω · ohm) : How strongly something opposes current.
$N$: Number from the first digits (no unit) : The digits of the code before the last one, read as one number (the 10 in 103).
$K$: Last digit of the code (no unit) : The number of zeros to add (the 3 in 103). On capacitors, 8 means × 0.01 and 9 means × 0.1.
$N$: Value from the EIA-96 table (no unit) : The three-digit number that the two digits of the code pick from the table of 96 values (code 01 is 100, code 68 is 499).
$M$: Multiplier letter (no unit) : What the letter at the end of an EIA-96 code means: A is × 1, B is × 10, C is × 100, X is × 0.1, Y is × 0.01.

How it works

A 3-digit code (usual for ±5 % parts) is two digits and a multiplier: 103 is 10 × 10³ = 10 kΩ and 221 is 22 × 10 = 220 Ω. A 4-digit code (usual for ±1 % parts) is three digits and a multiplier: 4702 is 470 × 10² = 47 kΩ. A small R stands for the decimal point: 4R7 is 4.7 Ω and R10 is 0.1 Ω. A code of 0, 00 or 000 is a 0 Ω jumper, a wire link in the shape of a resistor.

Very small ±1 % parts, such as the 0402 size, do not have room for four digits, so they use the EIA-96 code. The two digits (01 to 96) pick one of the 96 values of the E96 series from a table: 01 is 100, 24 is 174, 68 is 499, 96 is 976. The letter after them is the multiplier: A is × 1, B or H is × 10, C is × 100, D is × 1000, E is × 10 000, F is × 100 000, and X or S is × 0.1, Y or R is × 0.01 and Z is × 0.001.

Some codes have more than one reading. A text such as 47R is nearly always 47 Ω in R notation, but it would be 3.01 Ω as an EIA-96 code, because the letter R is also the multiplier × 0.01. The calculator shows both. When in doubt, measure the part, and check the resistor’s size and the board it came from.

Worked example

103: the first two digits are 10 and the last digit, 3, is the number of zeros to add: 10 × 1000 = 10 kΩ.
4702: the first three digits are 470 and the last one is 2, so 470 × 100 = 47 kΩ.
4R7: the R is the decimal point, so the value is 4.7 Ω.
01A: in the EIA-96 table, code 01 is 100, and the letter A means × 1, so the value is 100 Ω.
68X: code 68 is 499, and X means × 0.1, so 499 × 0.1 = 49.9 Ω. With the letter Y (× 0.01) the same digits, 68Y, would be 4.99 Ω.

Common questions

How do I tell a 3-digit code from an EIA-96 code?

Count the characters. Three digits (103) is the plain code. Two digits followed by a letter (01A) is EIA-96, and the letter tells you the multiplier. Four digits (4702) is a precise part. Codes with an R in them (4R7) show the decimal point.

What is a 000 or 0 resistor?

A zero-ohm link. It is a piece of wire in a chip-resistor body, used so that a machine can place it like any other part, or to let you choose between two routes on a board. It has almost no resistance, but it can still carry only a limited current, usually 1 A to 2 A.

Why is my resistor not marked at all?

The smallest chip resistors (0201 and 01005 sizes) are too tiny to print on. Check the reel or the bill of materials, or measure the part with a multimeter. Larger sizes, 0603 and up, are normally marked on the top.

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