BuddyPress.org

Take a look at the first few lines of file bp-core-avatars.php in the plugins/buddypress/bp-core directory.

/* Define settings for avatars. [TODO] This will eventually end up as admin configurable settings */

define( 'CORE_AVATAR_V1_W', apply_filters( 'bp_core_avatar_v1_w', 50 ) );

define( 'CORE_AVATAR_V1_H', apply_filters( 'bp_core_avatar_v1_h', 50 ) );

define( 'CORE_AVATAR_V2_W', apply_filters( 'bp_core_avatar_v2_w', 150 ) );

define( 'CORE_AVATAR_V2_H', apply_filters( 'bp_core_avatar_v2_h', 150 ) );

Currently they are not admin configurable yet, so keep not of the changes you make.