I have taken the same shoe size for over 20 years. I had heard that in the past few years people were having trouble finding the correct size for imported shoes/boots especially. Doc Martens are not being manufactured in England exclusively anymore. All the online size charts, including the size charts printed on the boxes themselves, are wrong. The charts are being made based on Chinese conversions, which are not correct. There are always 2 sizes between men's and women's sizes. a UK 7 is a US men's 7 or a US women's 9, or a EUR 40. whatever the size printed inside the boot is is the UK size. this is the size in US men's. add 2 to this and you will get the US women's size. this is the most common sizes listed with the correct conversions.
UK 5 = US Men's 5 or US women's 7
UK 6 = US men's 6 or US women's 8
UK 7 = US men's 7 or US women's 9
UK 8 = US men's 8 or US women's 10
UK 9 = US Men's 9 or US women's 11
UK 10 = US men's 10 or US women's 12
UK 11 = US men's 11 or US women's 13