One of my most commonly asked questions in relation to the Russian Cloche hat is about how to make smaller or larger sizes.
So I have worked up a size chart which I hope helps answer your questions.
The chart is for when as per instructions, you are using the 2.5mm crochet hooks and 4 ply cotton yarn, whether it's plain or mercerized. However normal cotton yarn has more stretch than the mercerized cotton.
The chart below gives the sizes from Premie up to Adult XXL. I have sourced the sizings from a variety of websites. It's funny because there is some slight variation on what is deemed to be the correct size and measurements for different ages, so I have averaged the results.
I would advise where possible to get a head measurement of the person who is going to be wearing the hats as I can say my 6 year old Sonofagun No.2 has a slightly smaller head than his female cousin who is 6 weeks younger than him!
The general rule of thumb with the Cloche hats is that they are made in slightly spiraling columns. Each column starts with one double crochet (US terms) which produces a column that is ultimately 3cm wide when the hat is worn. So a head that has a diameter of 48cm will need 16 dcs in the first round.
This chart can also be a good general guide for making any knitted or crocheted hat (just ignore the Double Crochet column!).
For example, if you are using a DK acrylic and one double crochet results in a 4cm column, for someone with the 48cm head diameter, you would only need to crochet 12 double crochets in the first row. Because 48 divided by 4 = 12.
I don't actually know if DK does produce that 4cm result. You'll have to work it out yourself!