It is normal to prick out seedlings into individual containers so the answer to your question is one!

May I suggest you purchase cell tray inserts,these come in either 15 & 24 cells sizes, and fit into a 14" x 8" tray, and are reusable, I have had mine for many years.

For Gypsophila I would normally use the 24 cell size,which generates plugs about 1.5" x 1.5" x 1.5"

Thanks for your suggestions Teegee, and could you just tell me - would I pinch out Gypsophila if so at what size?

I don't pinch them out as a rule because they branch naturally.

Plus the fact you don't say what type of Gypsophila you are growing.

The border type can grow quite tall whereas the alpine species spread.

I tend to use the former in baskets as it adds a bit of 'fluffy' width and height to the basket. I guess this is one of the reasons it is seen in bridal bouquets!

I use the alpine species to hang over kerbs and walls and for ground cover.

http://www.thegardenersalmanac.co.uk/Data/Gypsophila/Gypsophila.htm

Hi TeeGee, my apologies for not replying earlier, I have been on holiday. Thanks again for your response to my questions about gypsophilia, it was really helpful.