Not sure whether a gigabyte is bigger than a megabyte, or how many megabytes fit in a gigabyte? File size units can be confusing. This article breaks them all down in a clear reference chart with real-world examples.
Free Tool
PDF Compressor
Reduce PDF file size while preserving quality. Perfect for email attachments and uploads.
Try it now →What Are File Size Units?
The smallest unit of digital data is a bit — a single 0 or 1. Eight bits make one byte (B), which is the fundamental unit for measuring file sizes. A single ASCII character is roughly one byte.
Each step up multiplies by 1,024 (not 1,000) because computers work in binary and 2^10 = 1,024.
Conversion Chart — Bytes to Terabytes
Basic conversion table (B – TB)
| Unit | Full Name | In Bytes | Relationship |
|---|---|---|---|
| 1 B | Byte | 1 | — |
| 1 KB | Kilobyte | 1,024 B | 1 KB = 1,024 B |
| 1 MB | Megabyte | ~1.05 million B | 1 MB = 1,024 KB |
| 1 GB | Gigabyte | ~1.07 billion B | 1 GB = 1,024 MB |
| 1 TB | Terabyte | ~1.1 trillion B | 1 TB = 1,024 GB |
Larger units (PB – YB)
| Unit | Full Name | In Bytes | Real-World Scale |
|---|---|---|---|
| 1 PB | Petabyte | ~1 quadrillion B | Large enterprise data centers |
| 1 EB | Exabyte | ~1 quintillion B | Global monthly internet traffic |
| 1 ZB | Zettabyte | ~1 sextillion B | Total data generated worldwide per year |
| 1 YB | Yottabyte | ~1 septillion B | Theoretical — not yet reached in storage |
Quick Conversion Reference
| Conversion | Value |
|---|---|
| 1 KB → B | 1,024 B |
| 1 MB → KB | 1,024 KB |
| 1 MB → B | 1,048,576 B |
| 1 GB → MB | 1,024 MB |
| 1 GB → KB | 1,048,576 KB |
| 1 TB → GB | 1,024 GB |
| 1 TB → MB | 1,048,576 MB |
Real-World File Size Examples
Around 1 KB — Text and Email
| File Type | Typical Size |
|---|---|
| Plain text (~1,000 ASCII characters) | ~1 KB |
| Short email (text only) | 2–5 KB |
| HTML email (with formatting) | 20–50 KB |
Around 1 MB — Photos and Documents
| File Type | Typical Size |
|---|---|
| Smartphone photo (JPEG, standard) | 3–5 MB |
| Word document (text, a few pages) | 0.1–1 MB |
| Excel spreadsheet (several thousand rows) | 0.5–3 MB |
| PowerPoint (with a few images) | 3–10 MB |
| PDF (text, ~10 pages) | 0.5–2 MB |
| MP3 music file (3–4 min) | 3–5 MB |
Around 1 GB — Video and Apps
| File Type | Typical Size |
|---|---|
| Full HD video (MP4, ~10 min) | ~1 GB |
| Smartphone photos (JPEG) × 200–300 | ~1 GB |
| Mobile game app | 0.5–3 GB |
| Music album (MP3, ~12 tracks) | ~0.1 GB |
| Zoom meeting (video on, 1 hour) | 0.5–1.5 GB |
Around 1 TB — Storage Scale
| Content | Approximate Capacity |
|---|---|
| Full HD video | ~170 hours |
| Smartphone photos (JPEG) | ~200,000–300,000 |
| MP3 music tracks | ~200,000 |
| PDF documents | ~500,000 files |
File Size by Format
Business Documents
| Format | Typical Size | Notes |
|---|---|---|
| PDF (text) | 0.1–2 MB | Scanned-image PDFs can exceed 10 MB |
| PDF (with images) | 2–20 MB | Compression can reduce size significantly |
| Word (.docx) | 0.1–5 MB | Varies greatly with embedded images |
| Excel (.xlsx) | 0.05–10 MB | Macros increase size further |
| PowerPoint (.pptx) | 2–50 MB | Embedded photos and video add bulk |
| CSV | 0.01–5 MB | Text-only, so lightweight |
Image Files
| Format | Per-Image Estimate | Characteristics |
|---|---|---|
| JPEG (.jpg) | 0.5–5 MB | Best for photos; adjustable compression |
| PNG (.png) | 1–15 MB | Supports transparency; good for screenshots |
| WebP | 0.3–3 MB | ~30% smaller than JPEG; ideal for web |
| GIF | 0.1–5 MB | Animation support; limited color palette |
| RAW | 20–60 MB | Camera sensor data; editing use only |
| SVG | 0.005–0.1 MB | Vector; perfect for logos and icons |
Video and Audio Files
| Format | Per-Minute Estimate | Notes |
|---|---|---|
| MP4 (Full HD 1080p) | 100–150 MB | Most widely used video format |
| MP4 (4K) | 300–500 MB | High quality; storage-heavy |
| MOV | 100–200 MB | Apple default; similar to MP4 |
| MP3 | 1–1.5 MB | Standard music format (at 128 kbps) |
| WAV | 10–15 MB | Uncompressed; for production use |
| AAC | 0.8–1.2 MB | Better quality than MP3 at similar size |
Free Tool
Image Compressor
Compress JPEG, PNG, WebP, and HEIC images. Adjust quality, remove Exif data, and convert formats.
Try it now →Email Attachment Size Limits
Exceeding the size limit means your email won't send. Here are the limits for major services.
| Email Service | Attachment Limit | Fallback |
|---|---|---|
| Gmail | 25 MB | Auto-suggests Google Drive link |
| Outlook / Microsoft 365 | 20 MB | Switch to OneDrive link |
| Yahoo Mail | 25 MB | — |
| iCloud Mail | 20 MB | Mail Drop supports up to 5 GB |
Mbps vs MB — Speed vs Storage
These two abbreviations are easy to confuse.
| Mbps (Megabits per second) | MB (Megabyte) | |
|---|---|---|
| Measures | Data transfer speed | Storage capacity |
| Unit basis | bit | Byte (= 8 bits) |
Download Time Formula
File size (MB) × 8 ÷ Speed (Mbps) = Seconds
| File | Size | 50 Mbps | 100 Mbps | 1 Gbps |
|---|---|---|---|---|
| PDF document | 5 MB | 0.8 s | 0.4 s | 0.04 s |
| High-res photo | 20 MB | 3.2 s | 1.6 s | 0.16 s |
| Mobile app | 200 MB | 32 s | 16 s | 1.6 s |
| HD video | 1 GB | ~2.7 min | ~1.4 min | ~8 s |
Theoretical values. Actual speeds vary by network conditions.
Why Your Drive Shows Less Space Than Advertised
Bought a "1 TB" drive but it only shows 931 GB? This is due to different counting systems.
| System | Definition of 1 KB | Used By |
|---|---|---|
| Decimal (SI) | 1 KB = 1,000 B | Drive manufacturers |
| Binary | 1 KB = 1,024 B | Operating systems (Windows, etc.) |
The gap grows with larger capacities:
| Advertised | OS Display | Difference |
|---|---|---|
| 256 GB | ~238 GB | ~18 GB |
| 512 GB | ~476 GB | ~36 GB |
| 1 TB | ~931 GB | ~69 GB |
| 2 TB | ~1,863 GB | ~137 GB |
How to Reduce File Size
Compress Images
JPEG and PNG images can often be reduced by 50–80% with minimal visible quality loss. With sakutto's image compression tool, everything runs in your browser — files are never sent to a server.
Compress PDFs
Image-heavy PDFs benefit the most; halving the file size is common.
ZIP Compression
Bundling multiple files into a ZIP archive can reduce text-heavy content by 50–90%. Images and PDFs that are already compressed see little additional reduction from ZIP.
FAQ
How many MB is 1 GB?
1 GB = 1,024 MB. The binary multiplier is 1,024 (2^10), not 1,000.
What is the file size limit for email attachments?
Gmail allows 25 MB, Outlook allows 20 MB, and Yahoo Mail allows 25 MB. For larger files, use cloud storage links instead of attachments.
How large is a single photo?
A typical smartphone photo (JPEG) is about 3–5 MB. RAW images range from 20–50 MB, and PNGs from 5–15 MB.
What is the difference between Mbps and MB?
Mbps measures speed (megabits per second), MB measures storage (megabytes). Since 1 byte = 8 bits, a 100 Mbps connection theoretically transfers about 12.5 MB per second.
Why does my HDD show less space than advertised?
Manufacturers count 1 KB as 1,000 bytes, while operating systems count it as 1,024 bytes. A 1 TB drive therefore appears as roughly 931 GB in your OS.
Summary
File size units go B → KB → MB → GB → TB, each step multiplying by 1,024. The KB-to-GB range is what most people encounter daily.
Key takeaways:
- 1 MB = 1,024 KB, 1 GB = 1,024 MB, 1 TB = 1,024 GB
- A smartphone photo is about 3–5 MB; 10 minutes of Full HD video is about 1 GB
- Email attachment limits: Gmail 25 MB, Outlook 20 MB
- Speed (Mbps) and storage (MB) differ by a factor of 8
When files are too large, a compression tool makes quick work of trimming them down. Bookmark this chart so it's always at hand.
Free Tool
PDF Compressor
Reduce PDF file size while preserving quality. Perfect for email attachments and uploads.
Try it now →