freebsd man page for dh_size

DH_size(3SSL)							      OpenSSL							     DH_size(3SSL)

NAME
       DH_size - get Diffie-Hellman prime size

SYNOPSIS
	#include <openssl/dh.h>

	int DH_size(DH *dh);

DESCRIPTION
       This function returns the Diffie-Hellman size in bytes. It can be used to determine how much memory must be allocated for the shared secret
       computed by DH_compute_key().

       dh->p must not be NULL.

RETURN VALUE
       The size in bytes.

SEE ALSO
       dh(3), DH_generate_key(3)

HISTORY
       DH_size() is available in all versions of SSLeay and OpenSSL.

1.0.1e								    2013-02-11							     DH_size(3SSL)