Amazon S3 - how many objects in a bucket?

Sometimes we need to know how many objects there are in an S3 bucket. 

Unfortunately, Amazon does not give us an easy way to do it, and with large buckets with hundreds of thousand, even millions of objects, retrieving the list and counting is very tenous. 

Fortunately, Amazon tracks this number for us, and shows it in the usage reports. 

To create a usage report, first log into your AWS console. Then go to the billing center and select reports. This is a direct link but it may change. 

Select S3 (SImple Storage Service), and a monthly resolution. Download the resulting CSV file, open in Excel, and filter it to include only lines whose UsageType is StorageObjectCount.