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Rebecca Parker
H&M clothes sizes will become bigger following complaints from customers.
A spokesperson for the high street chain said: "We are taking the steps to change our womenswear measurements to be in line with UK sizing."
The Swedish company said the previous measurements and fit of a size 12 would now be the measurements of a size 10.
In March, shopper Rebecca Parker wrote an open letter complaining that despite being a 12/14 she struggled to fit into size 14 jeans at H&M.
"Why is it OK for a brand to label an item of clothing as a size which it clearly isn't," she asked.
She pointed out that while H&M sold items emblazoned with phrases such as #GRLPOWER or SISTERHOOD the shop's sizing policy was the opposite of empowering women.
She said that, at the age of 25, she was "thoroughly content" with her body but wonders how her teenage self would have reacted.
As a 13-year-old, she writes, she felt "podgy and sad when I had to reach for a garment that was labelled with a number in the high teens".
Speaking to the BBC following H&M's announcement, she said she was "really thrilled" her "nagging" had paid off.
"I just hope they follow through," she added.
Other customers had previously taken to Twitter to register their dissatisfaction with H&M's sizing.