Calculate disk space for Encryption at rest

We are planning to implement Encryption at rest using WiredTired Storage Engine

What is the percentage of disk space increase that would be required to account for after the encryption .
I am aware the Encryption at rest is wrapper for the Entire DB volume and the individual collections and fields are not encrypted as such …

Should the disk space increase ( if it does) be any concern for Encryption at rest

Similarly for Field level encryption , what is percentage of additional disk space that need to be accounted for ( For Eg : for a 1TB Mongodb Database)