Converting...
1 GB = 1 GB = 0.9313 GiB — binary (IEC) is 6.9% smaller than decimal (SI).
What Is a File Size?
Every digital file is stored as a sequence of binary digits — ones and zeroes. The smallest unit of digital information is a bit, which holds exactly one binary value. Eight bits group together to form a byte, and a byte is the fundamental building block for measuring file sizes. A plain ASCII character takes exactly one byte; a Unicode character can take two to four bytes.
From bytes, larger units are built up by multiplying by either 1,000 (the decimal SI standard) or 1,024 (the binary IEC standard). The confusion between those two multipliers is the source of nearly every "my hard drive shows the wrong size" question on the internet.
Decimal (SI) vs Binary (IEC) Units
There are two competing definitions for "kilobyte" and all larger units, and both are in active use today.
The SI (decimal) standard follows the International System of Units where "kilo" always means 1,000. Under this definition, 1 KB = 1,000 bytes, 1 MB = 1,000,000 bytes, and 1 GB = 1,000,000,000 bytes. Hard drive and SSD manufacturers use SI units because they make their products look larger — a "1 TB" drive actually contains exactly 1,000,000,000,000 bytes. Modern macOS also uses SI units.
The IEC (binary) standard, introduced in IEC 80000-13 (1998), defines units based on powers of 1,024 to match how computer hardware actually addresses memory. Under this standard, 1 KiB = 1,024 bytes, 1 MiB = 1,048,576 bytes, and 1 GiB = 1,073,741,824 bytes. RAM chips and CPU cache are always specified in binary units. Windows historically reported storage in binary units but labeled them "GB" instead of "GiB", causing the drive-size confusion that persists today.
| Property | Decimal (SI) | Binary (IEC) |
|---|---|---|
| Prefix multiplier | × 1,000 | × 1,024 |
| Unit names | KB MB GB TB PB | KiB MiB GiB TiB PiB |
| 1 GB in bytes | 1,000,000,000 | (not applicable) |
| 1 GiB in bytes | (not applicable) | 1,073,741,824 |
| Used by | Hard drives, SSDs, macOS, network speeds | RAM, Windows display, CPU cache |
| Divergence at 1 TB | 1,000 GB | ≈ 931 GiB |
File Size Unit Conversion Reference
Exact byte values for every standard unit:
| Unit | Full Name | Bytes | Standard |
|---|---|---|---|
| bit | Bit | 1/8 | — |
| B | Byte | 1 | SI |
| KB | Kilobyte | 1,000 | SI |
| MB | Megabyte | 1,000,000 | SI |
| GB | Gigabyte | 1,000,000,000 | SI |
| TB | Terabyte | 1,000,000,000,000 | SI |
| PB | Petabyte | 1,000,000,000,000,000 | SI |
| KiB | Kibibyte | 1,024 | IEC |
| MiB | Mebibyte | 1,048,576 | IEC |
| GiB | Gibibyte | 1,073,741,824 | IEC |
| TiB | Tebibyte | 1,099,511,627,776 | IEC |
| PiB | Pebibyte | 1,125,899,906,842,624 | IEC |
How to Convert File Sizes
Converting between SI units is straightforward: multiply or divide by 1,000 for each step. To go from GB to MB, multiply by 1,000. To go from MB to GB, divide by 1,000.
Converting between IEC units works the same way but with 1,024: to go from GiB to MiB, multiply by 1,024; to go from MiB to GiB, divide by 1,024.
Converting between SI and IEC units requires the exact ratio. To convert GB to GiB:
Worked example: 8 GB to MiB
Step 1: 8 GB × 1,000,000,000 bytes/GB = 8,000,000,000 bytes
Step 2: 8,000,000,000 ÷ 1,048,576 bytes/MiB = 7,629.39 MiB
The general formula: multiply the input value by the bytes-per-unit for the source unit, then divide by the bytes-per-unit for the target unit. This tool does this calculation using exact arithmetic so there is no floating-point rounding error.
Why Your Hard Drive Shows Less Space Than Advertised
This is the most searched file size question on the internet, and the answer is simple: no bytes are missing. The advertised capacity and the displayed capacity are the same number of bytes, just measured with different units.
1 TB drive: what actually happens
Manufacturer: 1 TB = 1,000,000,000,000 bytes (SI decimal)
Windows: 1,000,000,000,000 ÷ 1,073,741,824 = 931.32 GiB
Windows labels this "931 GB" — but means GiB
macOS: 1,000,000,000,000 ÷ 1,000,000,000 = 1,000 GB → "1 TB" ✓
Windows has historically displayed storage in GiB (binary bytes) but labeled the unit as "GB" — a misleading convention that has confused users since the 1990s. macOS switched to SI units in macOS Snow Leopard (2009) to match drive manufacturers. Linux tools vary: df -h uses IEC units, while df -H uses SI.
The divergence grows with size because it compounds at each prefix level. At 1 GB the gap is 6.87%. At 1 TB the gap is still 6.87% (the ratio is constant), but the absolute difference is now 68.7 GB — noticeable enough to confuse buyers who expect a "1 TB" drive to show "1,000 GB" everywhere.
Common File Sizes Reference
Approximate sizes for everyday file types, and how many fit on common storage capacities:
| File Type | Typical Size | 256 GB holds | 1 TB holds |
|---|---|---|---|
| 12MP JPEG photo | 3 MB | ~85,000 | ~333,000 |
| RAW photo (20MP) | 25 MB | ~10,000 | ~40,000 |
| 3-min MP3 (128 kbps) | ~3 MB | ~85,000 | ~333,000 |
| 1080p movie (2 h) | 4 GB | ~64 | ~250 |
| 4K movie (2 h) | 20 GB | ~12 | ~50 |
| Word document (text) | 50 KB | ~5 million | ~20 million |
| Mobile app (average) | 60 MB | ~4,000 | ~16,000 |
| Modern AAA game | 50 GB | ~5 | ~20 |
All counts are approximate. Actual file sizes vary by content, compression, and encoding settings.
File Transfer Time Guide
Transfer speeds are usually measured in megabits per second (Mbps) by ISPs and in megabytes per second (MB/s) by hardware vendors. Because there are 8 bits in a byte, divide an Mbps figure by 8 to get MB/s. A "100 Mbps" broadband connection transfers data at roughly 12.5 MB/s in practice.
| Connection | Typical Speed | Time to transfer 1 GB |
|---|---|---|
| Wi-Fi 5 (802.11ac) | ~75 MB/s | ~13 seconds |
| Wi-Fi 6 (802.11ax) | ~200 MB/s | ~5 seconds |
| 4G LTE (mobile) | ~10 MB/s | ~1 minute 40 seconds |
| USB 3.0 | ~400 MB/s | ~2.5 seconds |
| Gigabit Ethernet | ~125 MB/s | ~8 seconds |
| NVMe SSD (internal) | ~3,500 MB/s | < 1 second |
Speeds shown are real-world typical throughput, not theoretical maximum. Actual transfer times depend on protocol overhead, server load, and file system performance.
Frequently Asked Questions
How many bytes are in a gigabyte?
It depends on the standard. In the decimal (SI) system used by hard drive manufacturers and macOS, 1 GB = 1,000,000,000 bytes (one billion bytes). In the binary (IEC) system used by RAM and historically by Windows, 1 GiB = 1,073,741,824 bytes. The difference is about 7.4%.
What is the difference between GB and GiB?
GB (gigabyte) is a decimal unit: 1 GB = 1,000,000,000 bytes. GiB (gibibyte) is a binary unit: 1 GiB = 1,073,741,824 bytes. The IEC introduced the GiB notation in 1998 specifically to end the ambiguity. When you see RAM advertised as "16 GB" in a computer spec sheet, it almost always means 16 GiB.
Why does my 1 TB hard drive show only 931 GB?
Your drive contains exactly 1,000,000,000,000 bytes as advertised. Windows displays that number in GiB (divides by 1,073,741,824) and labels the result "GB". The calculation: 1,000,000,000,000 ÷ 1,073,741,824 = 931.32 GiB, which Windows rounds and labels as "931 GB". No bytes are missing — the units differ.
How do I convert MB to GB?
Divide by 1,000 to convert MB (megabytes) to GB (gigabytes) in the SI system. For example, 4,096 MB ÷ 1,000 = 4.096 GB. If you are working with MiB and GiB (binary), divide by 1,024 instead: 4,096 MiB ÷ 1,024 = 4 GiB.
How many MB in a GB?
1,000 MB in 1 GB (decimal/SI). Or 1,024 MiB in 1 GiB (binary/IEC). The answer depends on which system you are using. Most everyday contexts (file downloads, phone storage, streaming) use SI where 1 GB = 1,000 MB.
Why is 1 MB sometimes 1,000 KB and sometimes 1,024 KB?
This ambiguity existed before the IEC 80000-13 standard (1998) formally separated the two definitions. Before that standard, "megabyte" was used to mean both 1,000,000 bytes (SI) and 1,048,576 bytes (binary). The IEC introduced MiB (mebibyte) for the binary meaning. Old software, some operating systems, and some hardware still use the pre-standard meaning, which is why both interpretations persist.
What is a kilobyte (KB)?
In the SI standard: 1 KB = 1,000 bytes. In the older informal binary usage: 1 KB = 1,024 bytes (formally 1 KiB). For most practical purposes — email attachments, document files, web pages — the difference between 1,000 and 1,024 bytes is negligible. At gigabyte and terabyte scale, the difference becomes significant.
How many bits are in a megabyte?
1 MB = 1,000,000 bytes × 8 bits/byte = 8,000,000 bits (decimal/SI). Or 1 MiB = 1,048,576 bytes × 8 = 8,388,608 bits (binary/IEC). This distinction matters when comparing network speeds (measured in Mbps = megabits) with file sizes (measured in MB = megabytes).