GB vs GiB—and why downloads take longer
A “gigabyte” is not always the same number of bytes in every context. Storage labels commonly use decimal SI prefixes, while some software displays binary IEC prefixes. Connection speeds add another wrinkle: they are usually quoted in bits per second, not bytes per second.
Decimal GB and binary GiB
In the decimal SI system, each prefix multiplies by 1,000: 1 GB = 1,000,000,000 bytes. In the binary IEC system, each prefix multiplies by 1,024: 1 GiB = 1,073,741,824 bytes. A byte is eight bits, so uppercase B and lowercase b are not interchangeable.
For example, a drive sold as 1 TB contains 1,000,000,000,000 bytes using the decimal label. Dividing by 1,073,741,824 gives about 931.32 GiB. The data has not disappeared; the displayed number uses a different unit. Some products and operating systems use labels inconsistently, so inspect the unit definition rather than relying on a label alone.
Estimate download time
To estimate an ideal transfer time, convert the file size to bits and divide by the data rate in bits per second:
ideal seconds = file bytes × 8 ÷ connection bits per secondFor a decimal 80 GB file and a nominal 100 Mbps link:
80,000,000,000 bytes × 8 ÷ 100,000,000 bits/s
= 6,400 seconds
= 1 hour, 46 minutes, 40 seconds (ideal)This is a lower-bound-style arithmetic estimate, not a promise. The quoted access rate may be a maximum; actual throughput can vary with Wi-Fi, congestion, server capacity, protocol overhead, routing and other traffic. If you have a measured throughput, use that for a more realistic estimate.
Common conversion traps
100 Mbpsis 100 megabits per second. Dividing by eight gives an ideal 12.5 megabytes per second, before overhead.MB/sandMbpsdiffer by both capitalization and a factor of eight.- Do not assume
GBmeansGiB. Preserve the unit from the source when entering a size into a calculator. - Estimate with the same basis on both sides: decimal file size with decimal conversion, or explicitly convert to bytes before comparing.