Two options are available:-
1. Use Sticky tape as shown to measure the widest part of your nail (usually 1/3 up the nail), mark, then lay on a ruler to get the 'mm'. Always go up 1mm rather than risk a nail to small - I always include a few extra nails of varying sizes with your first order and a sizing kit for future orders and to share with loved ones who may wish to order. Do this for all 10 nails. I can then convert to match all shapes for you.
2. Request a sizing kit in our products at £1 with free delivery (ALL size nails in your chosen shape)
NB - Some shapes fit people better than others - active length may not be best if you have long nail beds (Pink part only). You may need a longer shape, despite filing your nails. I can always customise shapes to suit you if need. contact me if you are unsure - a sizing kits will be best for you in this case.