Amazon EBS charges calculation

Solution 1:

EBS is charged per-second (as of Sept 2017, before that it was per-hour) and it's against what you allocate. The minimum is 60 seconds.

The snapshots size is supposed to only be non-empty blocks since the allocation, and each subsequent snapshot is of the blocks that have changed since the last snapshot. EBS snapshots are still charged per-hour.

For 100GB gp2 it'll be charged about 20 minutes of usage (and some number of seconds) and assuming $0.10/GB/Month you should warn your bank about the incoming charge of about $0.0046.

Per-second announcement: https://aws.amazon.com/blogs/aws/new-per-second-billing-for-ec2-instances-and-ebs-volumes/

Cost calculation example: https://aws.amazon.com/ebs/pricing/

Thanks to @Vorsprung for the hint.

Solution 2:

EBS charges for space that you've allocated; so if you use 1GB on a 100GB volume, you'll be charged for 100GB. The clencher here is that you get charged on an hourly basis. I.e., 100GB would be $10 monthly, meaning if you kept the 100GB instance up for an hour, you'd be charged $0.0000039 for use.

If you store a SNAPSHOT, you'll be charged for the data that you actually use--because the snapshot process ignores empty pages. Take a look at the last section on the EBS page for details.