You can measure your feet standing on a piece of paper on a flat hard surface. It is easier if you can get someone to help. Draw around your foot. Now measure from your heel to longest toe. For the correct clog sandal size add on 5mm to 10mm.
* UK4 / US6 - 24.2cm long by 8cm at widest toe point
* UK4.5 / US6.5 - 24.6cm long by 8cm at widest toe point
* UK5 / US7 - 25.1cm long by 8.2cm at widest toe point
* UK5.5 / US7.5 - 25.4cm long by 8.2cm at widest toe point
* UK6 / US8 - 25.8cm long by 8.5cm at widest toe point
* UK6.5 / US8.5 - 26.4cm long by 8.5cm at widest toe point
* UK7 / US9 - 27.2cm long by 9cm at widest toe point
* UK7.5 / US9.5 - 27.5cm long by 9cm at widest toe point
The soles have EU sizes stamped on them but they deviate from standard sizing - therefore, I have listed them in UK/US sizes to make it easier to determine your correct size.