Type Function
Library (globals)
Return value Number
Revision 2017.3077
Keywords number, types, datatype
See also tostring()


Tries to convert its argument to a number. If the argument is already a number or a string that can be converted to a number, tonumber() returns the number, otherwise, it returns nil.

An optional argument (base) specifies the base to interpret the numeral.


tonumber( e [, base ] )
e (required)

The item to be converted to a number.

base (optional)

Number. Specifies the base to interpret the numeral. The base may be any integer between 2 and 36, inclusive. In bases above 10, the letter A (in either uppercase or lowercase) represents 10, B represents 11, and so forth, with Z representing 35. In base 10 (default), the number can have a decimal part as well as an optional exponent part. In other bases, only unsigned integers are accepted.


-- Convert the string "42" to a number (42)
local numString = "42"
local numValue = tonumber( numString )

if numValue ~= nil then
    print( numValue )