hmmm think you may have missed the point of the post.
it's not that i don't know that it's 5.6 weeks per year (or 28 days). it's what the formula is for working out what an entitlement is for a part year based on a specific start date etc.
the gov.uk gives you the number after you've asked all the questions, what i'm trying to scrape is what that actual formula is.
ie guys starts on 14 may 2019, holiday year starts on 1 jan 2019, works 5 days a week = 17.8 days (round up to 18).