Most mixes are measured in dried weight and come in bags ranging from 8 to 12 quarts. I have to say Burpee has changed a lot with their marketing strategy this year. Their seeds are cheaper, like a $1 a pack. They also offer a 10 quart coconut husk starter mix for under $4 at Lowes. That is pretty good.
Here are the basic brands I found in my area. They are all good for seed starting. They are typically sterile, water absorbent and hold fertilizers.
|Three Types of Seed Starting Mix: Gary Pilarchik|
|Jiffy Mix in My Hand & Miracle Grow Mix in the Cells: Gary Pilarchik|
|Jiffy (L) and Miracle Grow (R): Gary Pilarchik|