Data Storage Conversion Guide: GB, TB, MB, and More

11 min read•June 1, 2026•Reviewed: June 1, 2026

✓Reviewed by Apex Conversion Editorial Team · Last reviewed June 1, 2026

Data storage conversion is one of the most confusing measurement tasks in everyday computing because two incompatible systems — decimal (SI) and binary (IEC) — coexist and are often mislabeled. A hard drive sold as '1 TB' contains 1,000,000,000,000 bytes by decimal definition, but Windows may report it as approximately 931 GB because it uses a different counting system.

This guide explains exactly why the discrepancy exists, gives you the conversion factors for both systems, and answers the ten questions about storage units that confuse users most often.

The Two Systems: Decimal vs. Binary

Decimal (SI) system: uses powers of 1,000. 1 KB = 1,000 B. 1 MB = 1,000 KB = 1,000,000 B. 1 GB = 1,000 MB = 1,000,000,000 B. 1 TB = 1,000 GB = 1,000,000,000,000 B. Storage manufacturers (hard drives, SSDs, flash drives, cloud storage) always use decimal. macOS (since 10.6) and network engineers also use decimal.

Binary (IEC) system: uses powers of 1,024 (because 2¹⁰ = 1,024). 1 KiB (kibibyte) = 1,024 B. 1 MiB (mebibyte) = 1,024 KiB = 1,048,576 B. 1 GiB (gibibyte) = 1,024 MiB = 1,073,741,824 B. 1 TiB (tebibyte) = 1,024 GiB = 1,099,511,627,776 B. Traditional Windows File Explorer, RAM measurements, and some embedded systems use binary.

The confusion: manufacturers use decimal labels but older Windows versions display binary values. A '1 TB' drive has exactly 1,000,000,000,000 bytes. Windows File Explorer (pre-Windows 11 often) divides by 1,073,741,824 (1 GiB) instead of 1,000,000,000 (1 GB), showing ~931 GB. No bytes are missing — just different counting.

Key Conversion Formulas

━━━ DECIMAL (SI) SYSTEM ━━━
  KB  = B   ÷ 1,000     MB  = KB  ÷ 1,000     GB  = MB  ÷ 1,000
  TB  = GB  ÷ 1,000     PB  = TB  ÷ 1,000
  Rule: each step divides by 1,000

━━━ BINARY (IEC) SYSTEM ━━━
  KiB = B   ÷ 1,024     MiB = KiB ÷ 1,024     GiB = MiB ÷ 1,024
  TiB = GiB ÷ 1,024
  Rule: each step divides by 1,024

━━━ CROSS-SYSTEM CONVERSIONS ━━━
  1 GB (decimal) = 0.931323 GiB (binary)
  1 GiB = 1.073741824 GB
  1 TB  = 0.909495 TiB
  1 TiB = 1.099512 TB

━━━ SPEED (BANDWIDTH) ━━━
  MB/s = Mbps ÷ 8   (megabytes/s from megabits/s)
  Example: 100 Mbps internet = 12.5 MB/s download speed

Real-World Examples

Storage sizing: a 500 GB SSD (decimal) = 500,000,000,000 bytes ÷ 1,073,741,824 = 465.7 GiB (what Windows displays). A 4 TB hard drive = 4,000,000,000,000 bytes ÷ 1,099,511,627,776 = 3.637 TiB. This is why large drives seem smaller in Windows than advertised.

File sizes and downloads: a 4K movie download at 50 GB (decimal) = 50,000,000,000 bytes. At 100 Mbps internet speed = 12.5 MB/s = 12,500,000 bytes/second, download time = 50,000,000,000 ÷ 12,500,000 = 4,000 seconds ≈ 66.7 minutes. Note: internet speed Mbps uses 'bits' (lowercase b), not bytes (uppercase B).

Email and cloud storage: Gmail's 15 GB free storage = 15,000,000,000 bytes (decimal). A typical compressed photo is 3–8 MB = 3,000,000–8,000,000 bytes. At 5 MB average, 15 GB holds approximately 3,000 photos. A 1-hour HD video is about 1–2 GB at common quality settings.

Common Mistakes to Avoid

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Mistaking Mbps (megabits/second) for MB/s (megabytes/second): 100 Mbps ÷ 8 = 12.5 MB/s. Internet and cellular speeds are always listed in bits; file sizes and storage are always in bytes.
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Expecting a 1 TB drive to show 1 TB in Windows: older Windows reports in binary (GiB) while manufacturers label in decimal (GB). A '1 TB' drive shows as ~931 GB in older Windows — expected, not a defect.
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Using binary definitions for storage purchase decisions: manufacturer labels and cloud storage always use decimal. If a cloud service says '100 GB storage,' that is 100,000,000,000 bytes — compare to other services using the same definition.
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Confusing RAM and storage units: RAM capacity (e.g., 16 GB of RAM) typically uses binary GiB in practice, even if labeled GB. 16 GB RAM = 16 GiB = 17,179,869,184 bytes. Storage drives use decimal GB. This mixed usage is an industry convention inconsistency.

Frequently Asked Questions

How many GB is 1 TB?

In decimal: 1 TB = 1,000 GB exactly. In binary: 1 TiB = 1,024 GiB. Storage manufacturers use decimal; a '1 TB' drive holds exactly 1,000 GB = 1,000,000 MB = 1,000,000,000 KB = 1,000,000,000,000 bytes.

Why does my 1 TB hard drive show only 931 GB?

Older Windows divides bytes by 1,073,741,824 (1 GiB) to report 'GB.' 1,000,000,000,000 ÷ 1,073,741,824 = 931.32 GiB. No storage is missing — your drive has exactly 1 trillion bytes. macOS (since 2009) correctly shows '1 TB' using decimal.

How many MB is 1 GB?

In decimal: 1 GB = 1,000 MB exactly. In binary: 1 GiB = 1,024 MiB. Most practical uses (file sizes, storage capacity, cloud services) use decimal.

How many bytes is 1 GB?

1 GB (decimal) = 1,000,000,000 bytes exactly. 1 GiB (binary) = 1,073,741,824 bytes (= 2³⁰). Hard drive specs use decimal; older system memory specs sometimes use binary.

What is the difference between GB and GiB?

GB (gigabyte, decimal) = 1,000,000,000 bytes. GiB (gibibyte, binary) = 1,073,741,824 bytes. The GiB unit was standardized by the IEC in 1998 to resolve the ambiguity, but the GB label persists for both, causing ongoing confusion.

How fast can I download a 50 GB game?

Time = file size ÷ speed. At 500 Mbps (62.5 MB/s): 50,000 MB ÷ 62.5 = 800 seconds ≈ 13.3 minutes. At 100 Mbps (12.5 MB/s): 50,000 ÷ 12.5 = 4,000 s ≈ 66.7 minutes. At 25 Mbps (3.125 MB/s): 50,000 ÷ 3.125 = 16,000 s ≈ 4.4 hours.

How many photos fit in 1 GB?

JPEG photos from a smartphone typically range from 3–10 MB each. At 5 MB average: 1 GB (1,000 MB) ÷ 5 MB = 200 photos per GB. RAW camera files are 20–40 MB each: 1 GB holds about 25–50 RAW files.

What is a petabyte (PB)?

1 PB (decimal) = 1,000 TB = 1,000,000 GB = 10¹⁵ bytes. A petabyte of 5 MB photos would be 200 billion photos. Global internet traffic in 2024 exceeded 500 exabytes per month (1 EB = 1,000 PB = 10¹⁸ bytes).

How many GB is 1,000 MB?

Exactly 1 GB in decimal (SI): 1,000 MB = 1 GB. This is the definition. For binary: 1,000 MiB = 1,000 ÷ 1,024 GiB = 0.9766 GiB.

What does 'bits per second' vs. 'bytes per second' mean?

Bit (b, lowercase): the smallest unit of data (0 or 1). Byte (B, uppercase): 8 bits. Internet speeds are listed in bits/second (Mbps, Gbps) because network hardware transmits one bit at a time. File sizes are in bytes. To convert: divide Mbps by 8 to get MB/s. A 1 Gbps connection = 125 MB/s maximum throughput.

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