What Is a Gigabyte? Everything You Need to Know

4 min read•June 1, 2025•Reviewed: June 1, 2026

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

A gigabyte (GB) is approximately 1 billion bytes of digital data. It's the unit you encounter most in everyday technology: smartphone storage, laptop drives, internet data plans, and file downloads are all measured in gigabytes.

But the definition of a gigabyte is surprisingly nuanced. Hard drive manufacturers, operating systems, and internet service providers sometimes use the term differently — which is why your '128 GB' phone might only show 119 GB of available storage.

Gigabyte Defined

Decimal (SI standard, used by storage manufacturers):
  1 GB = 1,000,000,000 bytes (1 × 10⁹)
  1 GB = 1,000 MB = 1,000,000 KB

Binary (computing tradition):
  1 GiB = 1,073,741,824 bytes (2³⁰)
  1 GiB = 1,024 MiB

Ratio: 1 GB (decimal) = 0.931 GiB (binary)
  A '1 GB' drive is about 6.9% smaller than 1 GiB

1 GB of storage can typically hold:
  ~250 high-resolution photos (4 MB each)
  ~200 songs (5 MB each at 256 kbps AAC)
  ~3 minutes of 4K video
  ~30 minutes of HD video

Why Your Phone Shows Less Storage Than Listed

A '128 GB' phone ships with 128 billion bytes of storage (decimal). But the operating system — iOS and Android — reports storage in binary GiB (while still labeling them GB). 128,000,000,000 bytes ÷ 1,073,741,824 bytes/GiB = 119.2 GiB. Your phone shows about 119 GB.

Additionally, the operating system itself occupies several GB. iOS typically takes 5–8 GB; Android varies by manufacturer. Pre-installed apps, recovery partitions, and system files further reduce what you see as usable storage. A '128 GB' phone might have 110–115 GB of genuinely usable space.

Practical Gigabyte Reference

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Email: 1 GB holds roughly 50,000 plain-text emails or 500 emails with average attachments.
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Music: 1 GB ≈ 200 songs at typical streaming quality (256 kbps).
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Photos: 1 GB ≈ 250 smartphone photos (HEIF format) or 100 DSLR RAW files.
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Video: 1 GB ≈ 30 minutes of HD (1080p) video or 3–4 minutes of 4K/60fps.
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Apps: typical mobile apps range from 100 MB to 2+ GB; games can reach 4–8 GB.

Frequently Asked Questions

Is 1 GB 1,000 MB or 1,024 MB?

In decimal (SI) notation used by storage manufacturers: 1 GB = 1,000 MB. In binary (computing tradition): 1 GiB = 1,024 MiB. The gap is about 7.4%. macOS and most modern systems use decimal; older Windows versions used binary.

How many GB is 1 TB?

1 TB = 1,000 GB (decimal). In binary: 1 TiB = 1,024 GiB. A '1 TB' hard drive contains 1,000 GB in the manufacturer's decimal definition, which equals about 931 GiB in binary — which is why Windows used to show 931 GB for a 1 TB drive.