A student's open letter on Facebook questioning clothier H&M's sizing practices is gaining attention and led to an apology by the company.

Ruth Clemens, 25, a doctoral student at Leeds Trinity University, shared a photo on Facebook she had taken of herself in a pair of size 16 jeans she was unable to button.

She is normally a size 14.

"As I'm sure you're aware, size 16 is the largest size you stock (apart from in your plus size range, which is very limited in store and does not offer the range of styles for the fashion-conscious that are available in smaller sizes)," Clemens wrote. "I am not overweight (not that that should matter) and although I'm 5 foot 11 my body is pretty average shape-wise. It's already difficult enough for me to find clothes that fit well because of my height, why are you making jeans that are unrealistically small? Am I too fat for your everyday range? Should I just accept that accessible and affordable high street and on-trend fashion isn't for people like me?"

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The post has been shared more than 10,000 times. More than 8,000 people have left comments sharing similar experiences.

H&M responded to Clemens' post:

"We are sorry to hear about your experience in store recently. We always want our customers to have an enjoyable time when shopping in store and to leave feeling confident in themselves. At H&M we make clothing for all our stores around the world, so the sizing can vary depending on the style, cut and fabric. We value all feedback and will take on board the points you and other customers have raised."