Man page 9 : memparse

memparse - parse a string with mem suffixes into a number

unsigned long long memparse(const char *  ptr , char **  retptr );

ptr
    Where parse begins

retptr
    (output) Optional pointer to next char after parse completes

Parses a string into a number. The number stored at ptr is potentially suffixed with K (for kilobytes, or 1024 bytes), M (for megabytes, or 1048576 bytes), or G (for gigabytes, or 1073741824). If the number is suffixed with K, M, or G, then the return value is the number multiplied by one kilobyte, one megabyte, or one gigabyte, respectively.