Australian sizes are little bit different from European sizes, however they are much closer to UK. 

Generally speaking, we will advertise EU sizes on the product pages of our website, and EU sizing can be up to 2 sizes smaller than AU.

This is a broad rule, and won't apply to each individual item. 

Please refer to our size guide for specific information across all sizes, and if you have questions or feedback, don't hesitate to get in touch with our online team here: https://content.decathlon.com.au/help