PgAdmin 4 installation on Debian/Ubuntu
There are instructions on the pgAdmin site how to install with pip:


https://www.pgadmin.org/download/pip4.php


But there is no official Debian Package (.deb), yet. A request for packaging is pending:


https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=834129


For now, consider the Postgres Apt repository:

https://wiki.postgresql.org/wiki/Apt/FAQ