The "web TV meter" initially rolled out in 100 homes in June 2011, but that has now expanded to 500 further homes within the core BARB panel.
Created in collaboration with Kantar Media Audiences, the web TV meter gathers data on television viewing on computers.
Alongside PC and laptops, BARB is also currently testing a system for measuring TV viewing on tablet devices.
BARB has moved through proof of concept and testing with its web TV meter, and now hopes to implement reporting formats with the industry to "scale up production".
Bjarne Thelin, the chief executive of BARB, said: "Once rolled out, the web-TV meter will take reported viewing beyond the TV set and enable BARB to maximise reporting from our panel.
"It should also allow us to align panel reporting with other (server) data sets in future, potentially opening the door to develop ways to integrate such data into the BARB system."
The number of people in the UK who watch television via a PC or tablet has increased over the past year, but viewing via smartphones remains low, according to recent research by BARB.
A tracking study revealed that 15% of respondents had watched TV via a PC, laptop or tablet in November 2011, up from 14% at the same time in the previous year and 11% in November 2009.
BARB discovered that just 3% of people claimed to have watched TV via a mobile phone in November last year, although that was up from 2% in November 2010.
Broadcasters are finding that they can gather in much bigger audiences when factoring in all the screens where programming is available.
For example, Sky recently said that coverage of the key Manchester derby in the Premier League last season was watched by 4 million viewers in homes, but an additional 250,000 via its Sky Go multiplatform service.
BARB provides TV viewing measurement data obtained from a panel of 5,100 homes, returning data from 11,500 viewers.
These are mostly what is often called "overnights", giving the amount of viewers who sat down to watch a programme at its time of transmission - including any peaks of viewer activity.
But BARB also wants to give broadcasters the "bigger picture" of viewing data, involving the creation of a "comprehensive and cohesive cross-platform measurement tool".
This would include any consumption of programmes on-demand after their initial transmission, counting viewing across multiple devices such as tablets, smartphones and PCs.