[discrete]
[[esql-to_double]]
=== `TO_DOUBLE`
Converts an input value to a double value.

The input can be a single- or multi-valued field or an expression. The input
type must be of a boolean, date, string or numeric type.

Example:

[source.merge.styled,esql]
----
include::{esql-specs}/floats.csv-spec[tag=to_double-str]
----
[%header.monospaced.styled,format=dsv,separator=|]
|===
include::{esql-specs}/floats.csv-spec[tag=to_double-str-result]
|===

Note that in this example, the last conversion of the string isn't
possible. When this happens, the result is a *null* value. In this case a
_Warning_ header is added to the response. The header will provide information
on the source of the failure:

`"Line 1:115: evaluation of [TO_DOUBLE(str2)] failed, treating result as null. Only first 20 failures recorded."`

A following header will contain the failure reason and the offending value:

`"java.lang.NumberFormatException: For input string: \"foo\""`


If the input parameter is of a date type, its value will be interpreted as
milliseconds since the https://en.wikipedia.org/wiki/Unix_time[Unix epoch],
converted to double.

Boolean *true* will be converted to double *1.0*, *false* to *0.0*.

Alias: TO_DBL