There is no single definition of the voluntary sector. It is a term used to describe those organisations that focus on wider public benefit as opposed to statutory service delivery or profit. They are also known as civil society, the charity sector, Big Society, Third Sector, not-for-profit organisations or non-governmental organisations (NGOs). Not all of these organisations promote volunteering or even work with volunteers.
Voluntary sector organisations are diverse and range from small informal groups to significant enterprises with multi-million pound incomes. So there is no fully reliable way of calculating the overall size of the sector.
However there are over 180,000 registered charities in just England and Wales, with an income in excess of £52bn, so it is fair to assume that the actual total including all other voluntary activities is much larger.