float and real (Transact-SQL)
Applies to: 
SQL Server
Azure SQL Database
Azure SQL Managed Instance
Azure Synapse Analytics
Analytics Platform System (PDW)
Approximate-number data types for use with floating point numeric data. Floating point data is approximate; therefore, not all values in the data type range can be represented exactly. The ISO synonym for real is float(24).
Transact-SQL syntax conventions
Syntax
float [ (n) ] Where n is the number of bits that are used to store the mantissa of the float number in scientific notation and, therefore, dictates the precision and storage size. If n is specified, it must be a value between 1 and 53. The default value of n is 53.
| n value | Precision | Storage size |
|---|---|---|
| 1-24 | 7 digits | 4 bytes |
| 25-53 | 15 digits | 8 bytes |
Note
SQL Server treats n as one of two possible values. If 1<=n<=24, n is treated as 24. If 25<=n<=53, n is treated as 53.
The SQL Server float[(n)] data type complies with the ISO standard for all values of n from 1 through 53. The synonym for double precision is float(53).
Note
To view Transact-SQL syntax for SQL Server 2014 and earlier, see Previous versions documentation.
Remarks
| Data type | Range | Storage |
|---|---|---|
| float | - 1.79E+308 to -2.23E-308, 0 and 2.23E-308 to 1.79E+308 | Depends on the value of n |
| real | - 3.40E + 38 to -1.18E - 38, 0 and 1.18E - 38 to 3.40E + 38 | 4 Bytes |
Converting float and real data
Values of float are truncated when they are converted to any integer type.
When you want to convert from float or real to character data, using the STR string function is usually more useful than CAST( ). This is because STR enables more control over formatting. For more information, see STR (Transact-SQL) and Functions (Transact-SQL).
Prior to SQL Server 2016 (13.x), conversion of float values to decimal or numeric is restricted to values of precision 17 digits only. Any float value less than 5E-18 (when set using either the scientific notation of 5E-18 or the decimal notation of 0.000000000000000005) rounds down to 0. This is no longer a restriction as of SQL Server 2016 (13.x).
See also
ALTER TABLE (Transact-SQL)
CAST and CONVERT (Transact-SQL)
CREATE TABLE (Transact-SQL)
Data Type Conversion (Database Engine)
Data Types (Transact-SQL)
DECLARE @local_variable (Transact-SQL)
SET @local_variable (Transact-SQL)