Precision, Scale and Length

Precision is the number of digits present in a number. For example, the number 123.45 has a precision of 5

Scale is the number of digits to the right of the decimal point in a number. For example, the number 123.45 has a scale of 2.

Length is the number of bytes that are used to store the data. For example, length for a character string or Unicode data type is the number of characters. The length for binary, varbinary, and image data types is the number of bytes.

For example, an int data type can hold 10 digits, is stored in 4 bytes, and does not accept decimal points. The int data type has a precision of 10, a length of 4, and a scale of 0.

When two char, varchar, binary, or varbinary expressions are concatenated, the length of the resulting expression is the sum of the lengths of the two source expressions or 8,000 characters, whichever is less.

Example: 

Precision 5, scale 3   : 54.321
Precision 5, scale 1   : 5432.1
Precision 5, scale 0   : 54321
Precision 5, scale -1  : 54320

Precision 5, scale -3  : 54000