How storage capacity is measured on Apple devices
The storage capacity stated on your device’s packaging or specifications may differ from the capacity reported by its operating system or apps.
Decimal system (base 10)
Manufacturers of storage devices measure storage capacity using the decimal system (base 10). That’s why you may see statements such as this on the product packaging or specifications of your iPhone, iPad, Mac, Apple TV or other products:
1 GB = 1 billion bytes and 1 TB = 1 trillion bytes; actual formatted capacity less.
"Actual formatted capacity" means that the storage device's formatting uses some of this storage space. Additional storage space is used by factors such as the device's operating system.
Storage capacity measured using the decimal system is slightly larger than storage capacity measured using the binary system (base 2).
Binary system (base 2)
When storage capacity is measured using the binary system, 1 GB = 1,073,741,824 bytes and 1 TB = 1,099,511,627,776 bytes. Some apps and operating systems, such as iOS 10 and earlier and OS X Leopard and earlier, report storage capacity using the binary system.
Learn more
Manage storage space on iPhone or iPad
Manage storage space on Apple TV
Manage storage space on Apple Watch
