There should be two youth workers and four youth support workers for every secondary school catchment area, according to the National Youth Agency.
In a study of the South West it says this would mean increasing the current number by about 125% at a cost of £70m.
The agency, the professional body for youth work, said it estimated that £812m was needed to build a sufficient level of high quality youth provision across England.
Labour's manifesto promised a £95m investment in Young Futures Hubs, with youth workers, mental health support workers, and careers advisers on hand to support young people’s mental health and avoid them being drawn into crime.
The agency's research found there was currently an estimated 1,767 qualified youth workers and youth support workers in the South West while 3,996 were needed.
Director of youth work at the National Youth Agency Abbee McLatchie said the shortage of youth workers was felt more acutely in rural areas.
'Over the past 13 years, we've seen a huge cut to youth work across the whole country.
'We see huge disparities and inequality of access.
'This is often acutely felt particularly by younger people in rural and coastal communities who might already live in a community that doesn't have access to good transport and things to do.'
