In order to endow the woman that you love with an engagement ring without her knowledge – here are a few hints:

1.
If your future wife wears a ring on her left ring finger that take your chance when she changes the jewellery and bring the ring to the jeweller to measure it. Afterwards you put the ring back without attracting attention.

2.
Just put on of her rings on your finger and mark the spot with a pen until where you can put it on. After that you should not wash your hands!

3.
If your partner does not take the rings of to have enough time simply try to make an imprint. Therefore you can use a piece of soap, plasticine or any other soft material to get an imprint. The jeweller is able to define the size of the ring reliably.

4.
Should none of the above mentioned hints be possible paper and pencil work as well if you just trace the inner circle of the ring.