Just for clarification - the blockchain will grow in size even if there is no growth in the number of Bitcoin users or transaction volume.
Here's a graph with historical and up-to-date blockchain size.
https://blockchain.info/charts/blocks-size -- You can see the blockchain's growing ~700MB/month. If Bitcoin continues to grow in users and transactions, the rate of growth will increase. Aside light clients, there are other solutions being worked on regarding this issue.
Bitcoin holds some other files with the blockchain, which accounts for it being a GB or two over the size of the actual blockchain.