Formula to Calculate SharePoint 2010 Content Database

Database size = [(D × V) × S] + [10 KB × {L + (V × D)}]

Where

D = Number of documents

S = Average size of documents

L = List items

V = Number of non-current versions

10 KB = This value in the formula is a constant that roughly estimates the amount of metadata required by SharePoint Server 2010. If your system requires significant use of metadata, you may want to increase this constant.

As an example, let’s assume following values

Input	Value
Number of documents (D)	2,00,000*
Average size of documents (S)	250 KB
List items (L)	6,00,000
Number of non-current versions (V)	2**

* Calculated by assuming 10,000 users times 20 documents

**Assuming that the maximum versions allowed is 10

Database size = [(2,00,000 x 2) × 250] + [10 KB × {6,00,000 + (2,00,000 x 2)}] = 110,000,000 KB

Converting above result in GB will give around 105 GB

Refer Technet.Microsoft for reference.