Ring sizing
Ring size guide
Adjustable Ring sizers are very cheap online.
Adjustable Ring sizers are very cheap online.
However, there are methods you can do at home to get your size .
A good way is to get a piece of string and wrap it around your finger and mark where it overlaps, it's best to be a little tighter than loose . You then measure the length which will give you a good idea of your ring size.
Another quick way, is to measure an existing ring that fits, by measuring the inside diameter of the ring not including the metal .. this is also a good way of getting a loved ones measurements without having to ask them!

Size Guide (mm)
Size UK I ~ 15.04mm
Size UK J ~ 15.40mm
Size UK K ~ 15.80mm
Size UK L ~ 16.10mm
Size UK M ~ 16.51mm
Size UK N ~ 16.92mm
Size UK O ~ 17.35mm
Size UK P ~ 17.75mm
Size UK Q ~ 18.19mm
Size UK R ~ 18.61mm
Size UK S ~ 19.10mm
Size UK T ~ 19.51mm
Size UK U ~ 20.02mm
Size UK V ~ 20.32mm
Size UK W ~ 20.76mm
Size UK X ~ 21.18mm
Size UK Y ~ 21.49mm
Size UK Z ~ 21.89mm
Size UK N ~ 16.92mm
Size UK O ~ 17.35mm
Size UK P ~ 17.75mm
Size UK Q ~ 18.19mm
Size UK R ~ 18.61mm
Size UK S ~ 19.10mm
Size UK T ~ 19.51mm
Size UK U ~ 20.02mm
Size UK V ~ 20.32mm
Size UK W ~ 20.76mm
Size UK X ~ 21.18mm
Size UK Y ~ 21.49mm
Size UK Z ~ 21.89mm