A gigabyte (GB) is a unit of digital data equal to one billion bytes, as defined by the international system of units (SI). The 1,073,741,824-byte (2^30) unit is a gibibyte (GiB), which memory makers and some operating systems still label GB. It sits between the megabyte (MB) and the terabyte (TB). For buyers, the gigabyte matters most as the unit in which cloud storage, data transfer and many backup services are priced.
At a glance
- Decimal: 1 GB = 1,000,000,000 bytes (10^9). Binary counterpart: 1 gibibyte (GiB) = 1,073,741,824 bytes (2^30).
- The gap between the unit and its binary counterpart is about 7.4%.
- As a rough illustration, a high-definition film download, a large software installer or a phone backup is often a few gigabytes.
- Cloud storage is commonly priced per GB-month, and data egress per GB transferred.
- Server memory and virtual machine sizes are labelled GB, though the value is usually GiB.
What problem it solves
The gigabyte is the unit at which storage becomes a line item. It is small enough to price fine-grained services, such as a few hundred GB of block storage for a virtual machine, and large enough to describe whole applications, mailboxes and databases. Pricing per GB lets providers charge in proportion to use and lets buyers compare tiers and providers on a common basis, provided both sides mean the same gigabyte.
How it works
Decimal and binary values. 1 GB = 1,000 MB = 10^9 bytes in SI usage; 1 GiB = 1,024 MiB = 2^30 bytes. A drive or volume sold as 500 GB holds 500 billion bytes, which Windows displays as about 465 GB because it calculates in GiB but labels the result GB. The bytes are not missing; the units differ, apart from a little space used by formatting.
Storage pricing. Cloud object, file and block storage is usually billed per GB-month, often in tiers: hot tiers for frequently used data, cooler and archive tiers at a lower price per GB but with retrieval fees, minimum storage durations or minimum object sizes. Block storage is often billed on capacity provisioned rather than capacity used. See file systems and object storage for how the storage models differ.
Transfer pricing. Many cloud providers charge data egress fees per GB for data leaving their network or moving between regions, while inbound transfer is commonly free. At volume, egress can rival the storage charge itself.
Provisioned versus used. Some services charge for the capacity you allocate; others for what you actually store. Storage as a service (STaaS) offerings often combine a committed minimum with per-GB charges above it.
Our file and object storage and public cloud pages explain how we help buyers compare these pricing models.
When it matters for buyers
- Comparing cloud storage quotes. Normalize every quote to the same unit, tier and redundancy level before comparing per-GB prices.
- Forecasting egress. Estimate monthly GB leaving the cloud for users, backups, replication and analytics, not only storage size.
- Sizing virtual machines. Memory and disk are both quoted in GB; disk tier and size often affect cost and performance as much as the instance.
- Mailbox and SaaS quotas. Per-user storage allowances are usually set in GB, with charges for additional storage.
Questions to ask vendors
- Does your billing GB mean 10^9 or 2^30 bytes?
- Is storage billed on provisioned capacity or on capacity actually used, and how often is usage measured?
- What are the per-GB egress, inter-region and retrieval charges, and is there a free allowance?
- Do cheaper tiers have minimum storage durations, minimum object sizes or early-deletion fees?
- Are snapshots, replicas and versions billed per GB on top of the primary data?
How it differs from a gibibyte (GiB)
A gibibyte is exactly 2^30 bytes, about 7.4% more than a decimal gigabyte. Memory is sold in what are effectively GiB; drives are sold in decimal GB; some cloud providers bill in GiB while labelling it GB. When a price difference between two quotes is under about 8%, check whether the unit definition explains it. The glossary term Binary Prefixes lists the full set of binary units.