Doing the fresh spices thing and need some help with equipment.

Went today to a fabulous Indian store and purchased a range of spices
in plastic bags. Now, I'd like to transfer the spices from the
plastic bags into metal tins to prevent light exposure. My question
is, what size tins do I need?

The spice packets each contain 3oz of spices. And my first thought
was that all I needed were 4oz tins (2.375" width x 1.625" height).
Then it occured to me that this may be a fluid oz. versus weighted oz.
problem (i.e. the spice bags weigh 3oz or just less than 1/4 pound
while the containers hold 4oz or 1/2 cup, but that doesn't mean that
the one will fit into the other--3oz of feathers would never fit into
1/2 cup).

What size tins are in fact appropriate for 3 oz. of spices?

ecpepper