Data Size Converter
Convert between Bytes, KB, MB, GB, and TB for both binary (1024) and decimal (1000) systems, and calculate transfer times.
Binary Prefixes · Base 1024 (KiB · OS display)
Decimal Prefixes · Base 1000 (KB · Storage/Network display)
Download/Transfer Time Calculator
This calculation uses theoretical maximum speeds. In reality, protocol overhead and server conditions typically add 10-30% to transfer times. When an ISP advertises "100M Internet," it means 100 Mbps (100 million bits per second), which converts to approximately 11.9 MB/s. This difference between bits and bytes is why advertised speeds can appear 8 times faster.
💾 Why a 1TB hard drive shows up as 931GB: Manufacturers calculate 1TB as 1,000,000,000,000 bytes (decimal), while operating systems like Windows divide the same value by 1024, displaying it as 931 GiB, but labeling the unit as "GB." No capacity is lost; it's simply a difference in how it's measured.
What is the Data Size Converter?
Whether you're managing file sizes, disk capacity, or network speeds, converting data units is a common task. This converter simplifies it by calculating all units—from Bytes to Petabytes—in real time. Its key feature is the side-by-side display of binary (base 1024) and decimal (base 1000) prefixes, instantly clarifying why a 1TB hard drive appears as 931GB on your OS. It also includes a transfer time calculator to estimate download durations. It's free, requires no installation, and runs entirely in your browser.
How to use
- Enter a number into any field, such as 'GB' under the decimal section or 'GiB' under the binary section.
- As you type, all other units from 'Bytes (B)' to 'PiB' are converted and displayed automatically.
- Compare the values in 'Binary Prefixes · Base 1024' and 'Decimal Prefixes · Base 1000' to see the difference in measurement standards.
- To estimate transfer time, scroll to the 'Download/Transfer Time Calculator' and enter your 'Connection Speed', for example, 100 Mbps.
- The 'Estimated Time' to download or transfer the specified data size is calculated instantly.
- Click the 'Example' button to populate the fields with the size of a DVD, or 'Clear' to reset all values.
Data Size Converter guide
How this tool is used in real work, and what to watch out for.
Why a 1TB Hard Drive Shows Up as 931GB
The capacity isn't lost; it's just measured differently. Manufacturers market a 1TB drive as 1,000,000,000,000 bytes (using powers of 10). Windows, however, divides this same number by 1024 to display it as 931.32, but labels the unit as "GB." To be precise, it's 931.32 GiB, but the OS confusingly calls it GB.
There's a reason these two systems emerged. Memory's address structure made powers of 2 a natural fit for measuring capacity. In contrast, storage devices and network communications used SI prefixes (kilo = 1000) from the start. In 1998, the IEC introduced KiB, MiB, and GiB (binary prefixes) to clear up this confusion, but since operating systems continued to use KB and GB, the ambiguity persists today.
| Decimal Unit | Actual Bytes | Binary Conversion | Difference |
|---|---|---|---|
| 1 KB = 1,000 B | 1,000,000 | 0.977 KiB | -2.3% |
| 1 MB = 1,000² B | 1,000,000 | 0.954 MiB | -4.6% |
| 1 GB = 1,000³ B | 1,000,000,000 | 0.931 GiB | -6.9% |
| 1 TB = 1,000⁴ B | 1,000,000,000,000 | 0.909 TiB | -9.1% |
| 1 PB = 1,000⁵ B | 1,000,000,000,000,000 | 0.888 PiB | -11.2% |
Mbps vs. MB/s — An 8x Difference
Here lies the answer to the question, "Why do I only get 100 MB/s on my gigabit internet?" Network speeds are measured in bits (b), while file sizes are measured in bytes (B), and 1 byte equals 8 bits.
A lowercase 'b' stands for bit, while an uppercase 'B' stands for byte. This single character represents an eightfold difference.
| Advertised Speed | Actual Spec | Theoretical Max Download Speed |
|---|---|---|
| 100M Internet | 100 Mbps | Approx. 12.5 MB/s (11.9 MiB/s) |
| 500M Internet | 500 Mbps | Approx. 62.5 MB/s |
| 1G (Gigabit) Internet | 1 Gbps | Approx. 125 MB/s (119 MiB/s) |
| 50Mbps Average LTE | 50 Mbps | Approx. 6.25 MB/s |
How to Calculate Download Time
However, this is a theoretical maximum. Protocol overhead (like TCP and HTTP headers), server-side limitations, and losses from your router and Wi-Fi connection typically add 10-30% to the total time. It's common for Wi-Fi speeds to be less than half of what's advertised.
- Enter the file size into any of the top fields. For example, enter 4.7 in the GiB field (the size of one DVD).
- In the speed section below, enter a value and unit, or click one of the preset chips. For example, 100Mbps.
- The result will appear under "Estimated Time." Downloading 4.7 GiB at 100 Mbps takes about 6 minutes and 44 seconds.
- Check the "Speed conversion" line to see that same speed expressed in both MiB/s and Mbps.
Which Unit Is Used Where: A Quick Guide
| Where you see it | Base | Notes |
|---|---|---|
| Windows Explorer | 1024 (but labeled KB·MB·GB) | Technically KiB·MiB·GiB |
| macOS Finder | 1000 | Switched to decimal in 10.6 — a 1TB disk displays as 1TB |
| Linux `du -h` / `df -h` | 1024 | The `--si` flag uses a base of 1000 |
| nginx `client_max_body_size 8m` | 1024 (8,388,608 B) | The `k`, `m`, and `g` suffixes in config files are binary |
| PHP `upload_max_filesize 8M` | 1024 | Same as above |
| "100GB" Mobile Data Plan | Usually 1000 | Telecom standards use decimal |
| Storage Device Specs | 1000 | Manufacturers always use decimal |
Frequently asked questions
Is 1 KB equal to 1000 or 1024 bytes?
It depends on the context, which is a common source of confusion. Storage manufacturers use 1 KB = 1000 bytes (decimal). Operating systems use 1 KiB = 1024 bytes (binary) but often label it 'KB'. This tool shows both standards to eliminate ambiguity.
Why does my 1TB hard drive show up as only 931GB?
Manufacturers define 1TB as 1 trillion bytes. However, operating systems like Windows calculate capacity using base-1024, so they divide 1 trillion by 1024 three times, which equals ~931 GiB. The OS then often incorrectly labels this as 'GB'.
My internet is 100 Mbps. Why is my max download speed ~12.5 MB/s?
Internet speed is marketed in mega**bits** per second (Mbps), while file sizes are in mega**bytes** (MB/s). Since 1 Byte equals 8 bits, a 100 Mbps connection has a theoretical max speed of 12.5 MB/s (100 divided by 8).
Are the data sizes I enter stored on your server?
No. All calculations are performed entirely within your web browser. None of the data you enter, such as file sizes or connection speeds, is ever sent to our servers. Your information stays private on your device.