  Quantum engineering seeks to exploit quantum information to build, among
others, computing, cybersecurity, and metrology technologies. Quantum Software
Engineering (QSE) focuses on the information processing side of these
technologies. Historically, quantum (software) engineering has focused on
development in controlled research environments and 'in the small'. As the
field progresses, we should expect to see more large-scale quantum systems to
be deployed as 'real-world' products and services. An essential tool in
(classical) software engineering and development has been software size
metrics. Calculating/estimating the size of a piece of software, to be
developed or pre-existing, is an essential step in its engineering. Quantum
software will be no different. Here we introduce Q-COSMIC, a technique for
measuring the functional size of quantum software, based on the well-regarded
COSMIC standard (ISO/IEC19761) for classical software
