1 to 2 teaspoons for calcium deficiency is what I found in an internet search. If its what you have on hand, it will work but it might take a little bit of time to become available. There's other things I would be reaching for first (powdered dolomite for example) if its on hand. It will also supply magnesium.
Personally, I use epsom salts during veg and cal/mag during flower. (There's even been times I've used both cal/mag and epsom salts during flower too.) For me, it's been the simplest way to avoid both calcium and magnesium deficiencies indoors.