> Amazon S3 storage usage is calculated in binary gigabytes (GB), where 1 GB is 2^30 bytes. This unit of measurement is also known as a gibibyte (GiB), defined by the International Electrotechnical Commission (IEC). Similarly, 1 TB is 2^40 bytes, i.e. 1024 GBs.

Just scroll down a bit. It's in the "S3 Pricing Details" section of that page you linked to: (https://aws.amazon.com/s3/pricing/#:~:text=Amazon%20S3%20sto....)