$ man java
...
-Xmxsize
Specifies the maximum size (in bytes) of the memory allocation pool in bytes. This value
must be a multiple of 1024 and greater than 2 MB. Append the letter k or K to indicate
kilobytes, m or M to indicate megabytes, g or G to indicate gigabytes. The default value
is chosen at runtime based on system configuration. For server deployments, -Xms and
-Xmx are often set to the same value. See the section "Ergonomics" in Java SE HotSpot
Virtual Machine Garbage Collection Tuning Guide at
http://docs.oracle.com/javase/8/docs/technotes/guides/vm/gctuning/index.html.
The following examples show how to set the maximum allowed size of allocated memory to
80 MB using various units:
-Xmx83886080
-Xmx81920k
-Xmx80m
The -Xmx option is equivalent to -XX:MaxHeapSize.
...