Everyday Data Size Reference
Data Size Units
Data is measured using a hierarchy of units, each representing a larger quantity of bytes. Understanding these units is essential for managing storage, estimating download times, and making informed decisions about data plans and hardware:
| Unit | Symbol | Binary (Power of 2) | Decimal (Power of 10) |
|---|---|---|---|
| Byte | B | 1 byte | 1 byte |
| Kilobyte | KB | 1,024 bytes (2¹⁰) | 1,000 bytes (10³) |
| Megabyte | MB | 1,048,576 bytes (2²⁰) | 1,000,000 bytes (10⁶) |
| Gigabyte | GB | 1,073,741,824 bytes (2³⁰) | 1,000,000,000 bytes (10⁹) |
| Terabyte | TB | 1,099,511,627,776 bytes (2⁴⁰) | 1,000,000,000,000 bytes (10¹²) |
| Petabyte | PB | 1,125,899,906,842,624 bytes (2⁵⁰) | 1,000,000,000,000,000 bytes (10¹⁵) |
Binary vs. Decimal: What's the Difference?
There are two competing standards for data size units, which can lead to confusion:
Binary (IEC standard): Uses powers of 2. 1 KB = 1,024 bytes. Common in computing and programming.
Decimal (SI standard): Uses powers of 10. 1 KB = 1,000 bytes. Common in networking and some storage specifications.
New binary prefixes (KiB, MiB, GiB) were introduced to resolve ambiguity, but KB/MB/GB remain widely used for binary in practice.
For everyday use, the difference is small (~2.4% at the gigabyte level) but grows larger at higher units.
Common File Sizes
Use this reference to estimate typical file sizes for common content types:
| File Type | Typical Size | Range |
|---|---|---|
| Text document (DOCX) | 25-100 KB | Depends on images and formatting |
| PDF (text-only) | 100-500 KB | Multi-page with formatting |
| PDF (with images) | 1-10 MB | Depends on image resolution |
| JPEG photo | 1-5 MB | 6-12 MP resolution |
| PNG image | 2-10 MB | Lossless, larger than JPEG |
| MP3 audio (3 min) | 3-5 MB | 128-192 kbps |
| MP4 video (1 min) | 10-50 MB | 720-1080p |
| Feature film (2 hr) | 2-8 GB | 1080p to 4K Blu-ray |
Storage Capacity Estimates
How much data can common storage devices hold?
| Storage Device | Capacity | What It Can Hold |
|---|---|---|
| CD-ROM | 700 MB | 1 CD-quality album or ~350 JPEG photos |
| DVD | 4.7 GB | 1 feature film or ~2,000 photos |
| Blu-ray | 25-50 GB | 1-2 4K films or ~10,000 photos |
| USB flash drive | 16-128 GB | Hundreds of thousands of documents or thousands of photos |
| External HDD | 1-4 TB | Massive media libraries (~250,000 photos at 5 MB each) |
| Cloud storage | Variable | From 5 GB (free tier) to unlimited (enterprise) |
Bandwidth and Download Times
Internet speed is measured in bits per second (bps), not bytes. Understanding this is crucial for estimating download times:
1 byte = 8 bits
To estimate download time: File size (in bytes) × 8 ÷ bandwidth (in bits/sec)
Example: Downloading a 100 MB file on a 100 Mbps connection
Time = (100 MB × 8) ÷ 100 Mbps = 800 Mb ÷ 100 Mbps = 8 seconds (theoretical, before overhead)
| Bandwidth | 100 MB File | 1 GB File | 1 TB File |
|---|---|---|---|
| 10 Mbps | 80 sec | 13.3 min | 22.2 hr |
| 50 Mbps | 16 sec | 2.7 min | 4.4 hr |
| 100 Mbps | 8 sec | 1.3 min | 2.2 hr |
| 500 Mbps | 1.6 sec | 16 sec | 26.7 min |
| 1 Gbps | 0.8 sec | 8 sec | 13.3 min |
Frequently Asked Questions
In computing (binary), there are 1,024 bytes in a kilobyte (KB). In the decimal SI standard, there are 1,000 bytes. The binary definition is more commonly used in programming and software contexts.
MB (megabyte) and MiB (mebibyte) both represent approximately one million bytes, but they use different standards. MB can mean 1,000,000 bytes (decimal) or 1,048,576 bytes (binary), while MiB specifically means 1,048,576 bytes (strictly binary). MiB was introduced to eliminate ambiguity.
A typical smartphone or DSLR photo ranges from 2-8 MB for JPEG format, depending on resolution and compression settings. Raw (uncompressed) photos can be 20-50 MB each. A 12 MP camera produces approximately 3-5 MB per JPEG photo.
A terabyte (TB) contains approximately 1 trillion bytes (1,000,000,000,000 in decimal) or 1,099,511,627,776 bytes (binary). This equals about 250,000 high-quality photos, 500 hours of HD video, or millions of text documents. A TB is enough for most personal or small business storage needs.