Go.On UK has produced a "digital exclusion heatmap", pinpointing the areas where people are least likely to succeed in an evolving digital age.
It shows Wales has the lowest levels of internet access and only 62% of adults have the five basic digital skills.
Conwy county, Pembrokeshire and Anglesey are among the Welsh counties where digital exclusion is high.
The heatmap has measured the "likelihood of digital exclusion" based on social and digital indictors such as age, gender, broadband coverage and the five basic digital skills - managing information, communicating, transacting, creating and problem-solving.
Blaenau Gwent has the lowest number of adults possessing all five basic digital skills at 69%, compared to Ceredigion which has the highest percentage with 80% of adults.
Nearly half of adults on Anglesey have never been online, the highest percentage in Wales, while just 13.2% have never accessed the internet in Cardiff and the Vale of Glamorgan.
Rachel Neaman, chief executive of the charity, said: "Digital competency is an essential skill for everyone and we believe that - without urgent action - the nation's lack of basic digital skills will continue to hold back economic growth, productivity and social mobility."
The heatmap was produced in partnership with the BBC, the Local Government Association and the London School of Economics and Political Science.
More than a third of people in Wales do not have five basic digital skills, a charity has claimed.