By definition, FLOAT(n) should store the mantissa of the floating number in n bits. For example, FLOAT(16) should have a precision one-byte less than FLOAT(24). However, SQL Server 2005 only supports two precisions for floating numbers:

* Single Precision: FLOAT(24) or REAL, stored in 4 bytes, giving about 7 digits of precision, covering all types from FLOAT(1) to FLOAT(24),

* Double Precision: FLOAT(53), stored in 8 bytes, giving about 15 digits of precision, covering all types from FLOAT(25) to FLOAT(53).

The tutorial exercise below shows you some different precision and rounding examples:

-- FLOAT(1) works like FLOAT(24)

DECLARE @x FLOAT(1)

SET @x = 9.234567890E+10;

SELECT @x;

GO

9.234568E+10 -- 7 digits precision

-- Single precision with rounding

DECLARE @x REAL; -- FLOAT(24)

SET @x = 9.234567890E+10;

SELECT @x;

GO

9.234568E+10 -- 7 digits precision

-- FLOAT(25) works like FLOAT(53)

DECLARE @x FLOAT(25);

SET @x = 9.2345678901234567890E+100;

SELECT @x;

GO

9.23456789012346E+100 -- 15 digits precision

-- Double precision with rounding

DECLARE @x FLOAT(53);

SET @x = 9.2345678901234567890E+100;

SELECT @x;

GO

9.23456789012346E+100 -- 15 digits precision