The most acurate way to get your ring size is to visit a jeweller and be professionally measured. However, if you are unable to do so I can send out a plastic ring sizer, second class, for you to measure yourself.
The responsibility of providing an acurate measurement is yours.
The ring shown in the photo is purely for illustrative purposes and not included in the price.
Alternatively the quickest (and cheapest) way is to order one direct from Amazon UK, here is the link.