What is the difference between KB and KiB?

KB (kilobyte) in SI mode equals 1,000 bytes. KiB (kibibyte) in binary mode equals 1,024 bytes. Hard drive manufacturers use SI (so a '1 TB' drive is 1,000,000,000,000 bytes), while operating systems traditionally use binary (so Windows shows it as ~931 GiB).

How do I calculate file transfer time?

Enter your file size, then enter your connection speed in the transfer time section. Remember that network speeds are measured in bits per second (Mbps), not bytes per second. 1 Mbps = 0.125 MB/s. This tool handles the conversion automatically.

Why does my 1 TB hard drive show as 931 GB in Windows?

Hard drive manufacturers advertise capacity using SI units (1 TB = 1,000,000,000,000 bytes). Windows displays storage using binary units (1 GB = 1,073,741,824 bytes). So 1,000,000,000,000 bytes ÷ 1,073,741,824 = ~931 GiB, displayed as '931 GB' in Windows.

A petabyte (PB) is 1,000 terabytes in SI mode or 1,125,899,906,842,624 bytes in binary mode. Large data centres, cloud storage providers, and internet backbone operators deal in petabytes. The entire printed collection of the US Library of Congress is estimated at about 10 TB.

How many bytes are in a gigabyte?

In binary mode (used by operating systems): 1 GB = 1,073,741,824 bytes (2^30). In SI/decimal mode (used by storage manufacturers): 1 GB = 1,000,000,000 bytes (10^9). The difference is about 7.4%.

Byte Calculator

Convert data sizes in binary (1024) and SI (1000) modes. Calculate transfer time at any speed.

Enter any data size to convert all units instantly.

Transfer Time Calculator

Connection speed

Enter a file size above and a connection speed to calculate transfer time.

Binary Reference Table (powers of 1024)

Unit	Symbol	Bytes (exact)	Power of 2

How to Use the Byte Calculator

Choose a mode — Binary (1024) for OS/developer use, or SI (1000) for storage manufacturer specs.
Enter a value in any field (Bytes, KB, MB, GB, TB, or PB) and all other fields update instantly.
Calculate transfer time by entering your connection speed in the panel below the converter.
Copy all using the button, or reference the table for the full powers-of-1024 breakdown.

Binary vs. SI (Decimal) Data Units

The confusion between binary and decimal data units is one of the most common sources of frustration in computing. When you buy a "1 TB" hard drive, the manufacturer uses SI units: 1 TB = 1,000,000,000,000 bytes. But when Windows reports the drive capacity, it historically uses binary units: 1 GiB = 1,073,741,824 bytes. So a 1 TB drive appears as about 931 GiB in Windows Explorer. macOS switched to SI units in OS X 10.6 Snow Leopard (2009), so a 1 TB drive correctly shows as about 1 TB on a Mac.

Binary Prefixes (IEC Standard)

To eliminate confusion, the International Electrotechnical Commission (IEC) introduced binary prefixes in 1998: kibibyte (KiB, 1,024 bytes), mebibyte (MiB, 1,048,576 bytes), gibibyte (GiB), tebibyte (TiB), pebibyte (PiB), and exbibyte (EiB). Despite the standard being 25+ years old, most operating systems and tools still use "KB" and "GB" to mean binary units. In this tool, "Binary mode" uses these IEC values but labels them with the familiar KB/MB/GB abbreviations as they appear in Windows and Linux.

File Transfer Speed vs. Data Size

Network speeds are almost always quoted in bits per second (bps), not bytes per second (Bps). Capital B = bytes, lowercase b = bits. There are 8 bits in a byte. So a 100 Mbps connection can transfer approximately 12.5 MB per second (100 ÷ 8). This distinction is critical when calculating how long it takes to download or upload a file. Internet service providers advertise in Mbps (bits), while download managers show progress in MB/s (bytes). The transfer calculator in this tool handles this conversion automatically.

Data Unit Quick Reference

A typical MP3 song is 3–5 MB. A 4K movie is 50–100 GB. A full Blu-ray disc holds up to 100 GB. A typical hard drive backup is 1–4 TB. Cloud providers like AWS S3 measure in petabytes. The entire English Wikipedia (text only) is about 22 GB. The human genome is about 3 GB. Understanding these reference points helps developers and sysadmins make quick estimates about storage requirements, transfer costs, and database sizing.

Developer Use Cases

Developers commonly need data size conversions when: allocating database field sizes (a VARCHAR(255) holds 255 bytes), configuring upload limits (max_upload_size in PHP/nginx), planning object storage (AWS S3 pricing per GB), designing API payloads (keeping JSON responses under 1 MB), and estimating bandwidth costs (data transfer fees in cloud providers). The file size estimator in this tool is particularly useful when you have a known number of items and an average item size, helping you predict total storage needs before provisioning infrastructure.

Frequently Asked Questions

KB (kilobyte) in SI mode = 1,000 bytes. KiB (kibibyte) in binary mode = 1,024 bytes. Hard drive manufacturers use SI (1 TB = 1,000,000,000,000 bytes), while operating systems traditionally use binary (Windows shows it as ~931 GiB).

Enter your file size in any unit, then enter your connection speed in the Transfer Time panel. Network speeds are in bits per second (Mbps) — divide by 8 to get bytes per second. This tool handles that conversion automatically.

Drive manufacturers use SI (1 TB = 10^12 bytes). Windows uses binary (1 GB = 2^30 = 1,073,741,824 bytes). So 10^12 ÷ 1,073,741,824 = ~931. macOS switched to SI in 2009 and shows the full 1 TB correctly.

In SI mode: 1 PB = 1,000 TB = 10^15 bytes. In binary mode: 1 PB = 1,125,899,906,842,624 bytes (2^50). Large data centres and cloud providers operate at petabyte scale. The entire US Library of Congress printed collection is ~10 TB — about 0.00001 PB.

Binary (OS): 1 GB = 2^30 = 1,073,741,824 bytes. SI (storage mfr): 1 GB = 10^9 = 1,000,000,000 bytes. The difference is 7.4%, which is why a "500 GB" drive shows as ~465 GB in Windows.