Women who pride themselves on being a sexy size 10 might be surprised to find out that they could actually be a size 14.
Researchers say that a women's pair of pants is more than 10cm bigger than it was 40 years ago, because women's hips have increased on average by 7.62cm over the last four decades.
A size 10 waist which was 60.96cm in 1975 has increased by 10.16cm to be 71.12 centimeters now.
So that pair of size 10 jeans you've just bought would have read 'Size 14' in 1975 – a process that Retro Chick fashion blogger Gemma Seager has labelled "vanity sizing".
According to Seager, fashion designers and clothing makers have had to secretly stretch clothing to disguise the fact that women have slowly gotten bigger over the years.
The Daily Express quoted Seager as saying: "There's definitely an element of trying to flatter women who are going to be delighted if they fit into a smaller dress."
She added: "Most women don't care that much what size is on the label as long as the garment fits them well."
And Seager – who started the Campaign for Clearer Clothing Sizes - says that not only is the sizing in women's clothing inaccurate, it also varies from store to store.
She said: "If you look back you can see a gradual change decade by decade, so someone who wears a modern Size 10 would be a Size 12 from the Eighties, a 14 in the Seventies and a 16 to 18 in vintage clothing from the Fifties.
"Retailers know it's a bonus if a woman finds an item she likes and it's a smaller size than she generally wears."
Seagar adds that men's clothes haven't been affected by vanity sizing at all.