Double vs Float : Swift

Swift has two data types (Double and Float) to hold the decimal values. Both of them hold the same decimal type values but have some differences.

The basic difference is around the size of memory they both use based on which their precision varies.

Let’s try to understand the differences between both with example.

Number of Digits

• The Double type is used to store values in up to 17 places. It starts from the leftmost side and reduces the digits from the right side of the value if exceeding 17 places.
• The Float type is used to store values in up to 8 places. It also starts from the leftmost side and reduces the digits from the right side of the value if exceeding 8 places.

var doubleVariable : Double = 1234567890.1234567890
var floatVariable : Float = 12345.12345

print(doubleVariable)
//this will print only 17 digits from left
//1234567890.1234567

print(floatVariable)
//this will print only 8 digits from left
//12345.123

Memory Size

• Double takes 8 bytes of memory.
• Float takes only 4 bytes of memory

var doubleVariable : Double = 1234567890.1234567890
var floatVariable : Float = 12345.12345

print(MemoryLayout.size(ofValue: doubleVariable))
//this will print
//8 (bytes)

print(MemoryLayout.size(ofValue: floatVariable))
//this will print
//4 (bytes)

Default Type

• If we don’t define any type and directly assign the value, the compiler initialises it as Double.

var defaultVariable = 1.00
var doubleVariable : Double = 1234567890.1234567890
var floatVariable : Float = 12345.12345

print(type(of: defaultVariable))
//this will print
//Double

print(type(of: doubleVariable))
//this will print
//Double

print(type(of: floatVariable))
//this will print
//Float

Conclusion

• The Double is more precise than the Float as it has more decimal digits.
• The Double takes more memory than the Float.
• If there no data type is defined explicitly and if we assign any decimal value to a variable, the compiler treats it as Double.

When to Use What

• For places where no extra precision is required, use Float. Like amount where up to 2 decimal digits can work.
• If confused about what to use and not sure where the value can go, use Double.