Understanding Terabytes and Gigabytes: A Comprehensive Guide
In the digital age, understanding data storage units is essential for everyone from casual users to IT professionals. Whether you're buying a new external hard drive, choosing a cloud storage plan, or simply trying to figure out how many movies your NAS can hold, the terms "terabyte" (TB) and "gigabyte" (GB) come up constantly. But what do they really mean, and why are there two different ways to convert between them? This comprehensive guide will answer all your questions.
1. What is a Terabyte (TB)?
A terabyte is a unit of digital information storage. The prefix "tera" comes from the Greek word for "monster," and it represents a massive quantity of data. In the context of computers and storage, there are actually two definitions of a terabyte:
- Decimal (SI) definition: 1 TB = 1,000,000,000,000 bytes (10¹² bytes). This is used by hard drive manufacturers, SSD makers, USB drive vendors, and cloud storage providers like Google Drive and Dropbox.
- Binary (IEC) definition: 1 TB = 1,099,511,627,776 bytes (2⁴⁰ bytes), technically called a tebibyte (TiB). This is used by operating systems like Windows, macOS, and Linux when displaying storage capacity.
2. What is a Gigabyte (GB)?
A gigabyte is a smaller unit of digital storage. The prefix "giga" means billion. Like terabytes, gigabytes have two definitions:
- Decimal (SI): 1 GB = 1,000,000,000 bytes (10⁹ bytes)
- Binary (IEC): 1 GB = 1,073,741,824 bytes (2³⁰ bytes), technically called a gibibyte (GiB)
3. The Decimal vs Binary Confusion: Why Two Standards?
The confusion between decimal and binary units dates back to the early days of computing. Computers work in binary (base-2) because they use electronic switches that have two states: on (1) and off (0). This makes powers of 2 (2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, etc.) natural for computer architecture.
However, when storage devices became consumer products, manufacturers found it easier to use decimal units (base-10) for marketing. After all, 1 TB sounds more impressive than 0.909 TiB, and it's simpler for most people to understand. This created a persistent discrepancy that confuses consumers to this day:
- A drive sold as "1 TB" contains exactly 1,000,000,000,000 bytes (decimal)
- Windows reports this as 931 GB because it divides by 1,073,741,824 bytes per binary GB (or 1,099,511,627,776 per binary TB)
4. TB to GB Conversion: The Math
When converting terabytes to gigabytes, you need to know which system you're using:
- Decimal (SI) conversion: Multiply by 1000. Example: 5 TB × 1000 = 5,000 GB
- Binary (IEC) conversion: Multiply by 1024. Example: 5 TB × 1024 = 5,120 GB (technically 5 TiB = 5,120 GiB)
Our converter above shows both results instantly, so you don't have to remember which is which.
5. Real-World Examples: How Much is 1 TB?
To put these numbers in perspective, here's what you can typically store in 1 terabyte (decimal):
- Photos: Approximately 250,000-300,000 photos from a 12-megapixel camera (at standard JPEG compression)
- Music: About 250,000 songs encoded at 4 minutes per song (128 kbps MP3)
- Video: Roughly 500 hours of standard definition video, or 250 hours of HD video
- Movies: Approximately 250 feature-length films (4 GB each in compressed format)
- Documents: Approximately 500 million pages of plain text (assuming 2 KB per page)
6. Common Storage Scenarios and Their TB/GB Requirements
External Hard Drives: A "5 TB" external drive (decimal) actually provides about 4.55 TiB of usable space in binary terms. That's a loss of nearly 0.45 TB due to the different measurement systems, before even accounting for file system formatting!
NAS (Network Attached Storage): A 4-bay NAS with four 10 TB drives in RAID 5 provides roughly 27.2 TB of usable space in decimal, but your computer will show about 24.7 TiB. Understanding the difference is crucial for capacity planning.
Cloud Storage: Most cloud providers advertise in decimal terabytes. A 2 TB Google Drive plan gives you exactly 2,000,000,000,000 bytes of quota. However, when you check your usage in the Google Drive app on your computer, it might show the used space in binary gigabytes (GiB), which can be confusing. Uploading 1 TiB of files will consume approximately 1.1 TB of your decimal quota.
7. Why Does a 1 TB Drive Show Only 931 GB in Windows?
This is the most common question about storage. Here's the detailed explanation:
- Drive manufacturers use decimal units: 1 TB = 1,000,000,000,000 bytes
- Windows uses binary units: 1 GB = 1,073,741,824 bytes (2³⁰ bytes)
- To calculate what Windows shows: 1,000,000,000,000 ÷ 1,073,741,824 = 931.32 GB
The same principle applies to any drive size. A 2 TB drive shows about 1.86 TB in Windows, a 4 TB drive shows about 3.63 TB, and so on. This is not a defect—it's a unit mismatch.
8. Data Transfer: Bits vs Bytes
Another common source of confusion is data transfer speeds. Internet speeds are advertised in bits per second (Mbps, Gbps), while file downloads show bytes per second (MB/s, GB/s). The conversion is straightforward:
- 1 byte = 8 bits
- 1 MB/s = 8 Mbps
- 100 Mbps internet = 12.5 MB/s maximum download speed
- 1 Gbps internet = 125 MB/s maximum download speed
This is why your "1 Gbps" fiber connection downloads files at about 110-115 MB/s in practice (accounting for protocol overhead).
9. The IEC Binary Prefixes: A Solution to the Confusion
To resolve the ambiguity, the International Electrotechnical Commission (IEC) introduced binary prefixes in 1998:
- Kibibyte (KiB): 1,024 bytes
- Mebibyte (MiB): 1,024 KiB = 1,048,576 bytes
- Gibibyte (GiB): 1,024 MiB = 1,073,741,824 bytes
- Tebibyte (TiB): 1,024 GiB = 1,099,511,627,776 bytes
- Pebibyte (PiB): 1,024 TiB = 1,125,899,906,842,624 bytes
Unfortunately, these prefixes haven't been widely adopted in consumer marketing, but they appear in technical documentation and some Linux utilities. When you see "TiB" or "GiB", you know you're dealing with binary units.
10. TB to GB Conversion Table for Quick Reference
Here's a handy reference for common conversions (both decimal and binary):
- 0.5 TB = 500 GB (decimal) / 512 GB (binary)
- 1 TB = 1,000 GB (decimal) / 1,024 GB (binary)
- 2 TB = 2,000 GB (decimal) / 2,048 GB (binary)
- 4 TB = 4,000 GB (decimal) / 4,096 GB (binary)
- 5 TB = 5,000 GB (decimal) / 5,120 GB (binary)
- 8 TB = 8,000 GB (decimal) / 8,192 GB (binary)
- 10 TB = 10,000 GB (decimal) / 10,240 GB (binary)
- 12 TB = 12,000 GB (decimal) / 12,288 GB (binary)
- 16 TB = 16,000 GB (decimal) / 16,384 GB (binary)
- 20 TB = 20,000 GB (decimal) / 20,480 GB (binary)
11. Frequently Asked Questions About TB and GB
Q: Why does my 4 TB external drive only show 3.63 TB?
A: Same reason as the 1 TB drive. 4,000,000,000,000 bytes ÷ 1,099,511,627,776 bytes per TiB = 3.63 TiB. Windows labels this as "TB" but it's actually TiB.
Q: How many GB are in 1 TB for mobile data plans?
A: Mobile carriers typically use decimal units. 1 TB = 1,000 GB. If you have a 1 TB data plan, you can use approximately 1,000 GB before hitting your limit.
Q: Is there an easy way to remember the conversion?
A: For rough estimates, remember that binary is about 7% larger than decimal. So 100 GB decimal ≈ 93 GiB, and 100 GiB ≈ 107 GB decimal. For terabytes: 1 TB decimal ≈ 0.909 TiB, and 1 TiB ≈ 1.1 TB decimal.
Q: When should I use decimal vs binary?
A: Use decimal when dealing with storage specifications (hard drives, SSDs, cloud plans). Use binary when working with operating system displays (Windows file explorer) or programming.
12. Advanced Topics: Beyond TB
As data storage needs grow, we encounter larger units:
- Petabyte (PB): 1,000 TB (decimal) or 1,024 TiB (binary) - used by large data centers
- Exabyte (EB): 1,000 PB - global internet traffic per day is several exabytes
- Zettabyte (ZB): 1,000 EB - all data in the world is estimated to be several zettabytes
- Yottabyte (YB): 1,000 ZB - beyond current comprehension
A single petabyte can store approximately 500 billion pages of text, or 13.3 years of HD video. Data centers today measure their capacity in exabytes.
13. Practical Tips for Managing Large Storage
Know your units: When buying storage, always check whether the manufacturer uses decimal or binary. Most consumer devices (external drives, NAS) advertise in decimal, but your operating system reports in binary.
Account for the "missing space": When planning a backup strategy, always account for the decimal-binary discrepancy. If you need to back up 10 TiB of data, you'll need at least 11 TB of storage (decimal).
Use our converter: Bookmark this page for quick conversions. Whether you're planning a backup strategy, checking if a drive will hold your media collection, or just curious, our tool handles both decimal and binary instantly.
Consider file system overhead: After the decimal-binary discrepancy, formatted drives lose additional capacity to file systems (NTFS, APFS, ext4). A 10 TB drive might show 9.09 TiB before formatting, and about 8.9 TiB after formatting with NTFS.
14. Conclusion
Understanding the difference between decimal and binary terabytes is crucial in today's digital world. The next time you see a "4 TB" drive showing only 3.63 TB in Windows, you'll know it's not a defect—it's simply a matter of units. Our TB to GB converter takes the guesswork out of the equation, giving you both decimal and binary results instantly. Bookmark this page for all your data conversion needs, and explore our other tools for GB to MB, MB to GB, and data transfer rate conversions.