float and real (Transact-SQL)
Applies to: 
SQL Server
Azure SQL Database
Azure SQL Managed Instance
Azure Synapse Analytics
Analytics Platform System (PDW)
SQL analytics endpoint in Microsoft Fabric
Warehouse in Microsoft Fabric
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).
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 |
The float and real data types are known as approximate data types. The behavior of float and real follows the IEEE 754 specification on approximate numeric data types. To understand how the Microsoft Visual C (MSVC) compiler uses the IEEE 754 standard, see IEEE Floating-Point Representation
Approximate numeric data types don't store the exact values specified for many numbers; they store a close approximation of the value. For some applications, the tiny difference between the specified value and the stored approximation isn't relevant. For others though, the difference is important. Because of the approximate nature of the float and real data types, don't use these data types when exact numeric behavior is required. Examples that require precise numeric values are financial or business data, operations involving rounding, or equality checks. In those cases, use the integer, decimal, numeric, money, or smallmoney data types.
Avoid using float or real columns in WHERE clause search conditions, especially the = and <> operators. It's best to limit float and real columns to > or < comparisons.
Converting float and real data
Values of float are truncated when they're converted to any integer type.
When you want to convert from float or real to character data, using the STR string function is typically more useful than CAST( ). The reason is that 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).