How it works
Internet plans usually quote bits per second; files are usually measured in bytes. A capital B means bytes, while a lowercase b means bits. GiB and MiB use powers of 1024. The default 85% is an editable planning assumption, not a measured connection speed.
The formulaSeconds = file size in bits ÷ (bits per second × usable speed ÷ 100)
1 byte = 8 bits · 1 GB = 1,000,000,000 bytes
1 byte = 8 bits · 1 GB = 1,000,000,000 bytes