DAVOS - The web economy of the G20 is projected to reach $4.2 trillion in 2016 - nearly double the size of $2.3 trillion in 2010, according to a study by a global management consulting firm.

The study by the Boston Consulting Group (BCG) and commissioned by Internet giant Google said the hike in the web economy will provide companies and countries with a vital source of growth as they battle to thrive in an era of uncertainty.

It assumes that in four years three billion people, or nearly 50 per cent of the world's population, will be using the internet. This is up from 1.9 billion users in 2010.

The rapid fall in the cost of smartphones - with cheap versions now costing about $100 - means that by 2016 about 80 per cent of all internet users will access the web using a mobile phone, it says.

In 2010, the internet economy in the G20 group of leading nations was worth $2.3tn - larger than the economies of Italy or Brazil, but a mere 4.1 per cent of the total size of all G20 economies.

The research point underlined that the emergence of a "new internet" will make web access not a luxury any more.

"The majority of web users will live in emerging markets (within four years)," it says.

China is expected to be home to 800 million people using the internet; that is more than the United States, India, France, Germany and the UK taken together.

The internet will go social, and allow customers and companies to engage with each other.