{"id":"mac-storage-basics.why-is-my-external-drive-smaller-than-advertised","url":"/faq/mac-storage-basics/why-is-my-external-drive-smaller-than-advertised","category":{"id":"mac-storage-basics","title":"Mac storage basics"},"subcategory":{"id":"external-storage","title":"External storage and adding space"},"question":"Why does my new external drive show less space than the box says?","alt_questions":["2tb drive shows 1.8tb","external drive capacity less mac","new ssd smaller than advertised","formatted capacity external drive","why 1tb shows 931gb"],"short_answer":"Mac shows decimal units like the box, so a 1 TB drive shows close to 1 TB minus format overhead. Much less suggests binary units in another tool or an extra partition.","answer_markdown":"On a Mac, a 1 TB drive should show close to 1 TB, because macOS and drive makers both count in decimal units. A little is used by the format's own structures and, on some drives, hidden partitions.\n\nIf you see a much smaller figure, such as 931 GB for a 1 TB drive, you're probably looking at a Windows tool or a utility that counts in binary units. A drive showing far less than either figure may have an extra partition — check **Disk Utility → View → Show All Devices**.","answer_html":"

On a Mac, a 1 TB drive should show close to 1 TB, because macOS and drive makers both count in decimal units. A little is used by the format's own structures and, on some drives, hidden partitions.

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If you see a much smaller figure, such as 931 GB for a 1 TB drive, you're probably looking at a Windows tool or a utility that counts in binary units. A drive showing far less than either figure may have an extra partition — check Disk Utility → View → Show All Devices.

","answer_text":"On a Mac, a 1 TB drive should show close to 1 TB, because macOS and drive makers both count in decimal units. A little is used by the format's own structures and, on some drives, hidden partitions.\n\nIf you see a much smaller figure, such as 931 GB for a 1 TB drive, you're probably looking at a Windows tool or a utility that counts in binary units. A drive showing far less than either figure may have an extra partition — check Disk Utility → View → Show All Devices.","tags":["capacity","external drive","disk utility"],"related":[{"id":"mac-storage-basics.why-does-my-256gb-mac-show-less-than-256gb","question":"Why does my 256 GB Mac show less than 256 GB of total storage?","url":"/faq/mac-storage-basics/why-does-my-256gb-mac-show-less-than-256gb"},{"id":"mac-storage-basics.how-do-i-erase-or-format-a-drive-on-a-mac","question":"How do I erase or format a drive on a Mac?","url":"/faq/mac-storage-basics/how-do-i-erase-or-format-a-drive-on-a-mac"}],"applies_to":"all","last_reviewed":"2026-10-01","title":"Why does my new external drive show less space than the box says? — Storage Studio FAQ","description":"Mac shows decimal units like the box, so a 1 TB drive shows close to 1 TB minus format overhead. Much less suggests binary units in another tool or an extra partition.","crumbs":[{"name":"Home","path":"/"},{"name":"FAQ","path":"/faq/"},{"name":"Mac storage basics","path":"/faq/mac-storage-basics/"},{"name":"Why does my new external drive show less space than the box says?","path":"/faq/mac-storage-basics/why-is-my-external-drive-smaller-than-advertised"}],"jsonld":{"@context":"https://schema.org","@type":"FAQPage","url":"https://storagestudio.us/faq/mac-storage-basics/why-is-my-external-drive-smaller-than-advertised","inLanguage":"en","dateModified":"2026-10-01","mainEntity":[{"@type":"Question","name":"Why does my new external drive show less space than the box says?","alternateName":["2tb drive shows 1.8tb","external drive capacity less mac","new ssd smaller than advertised","formatted capacity external drive","why 1tb shows 931gb"],"acceptedAnswer":{"@type":"Answer","text":"On a Mac, a 1 TB drive should show close to 1 TB, because macOS and drive makers both count in decimal units. A little is used by the format's own structures and, on some drives, hidden partitions.\n\nIf you see a much smaller figure, such as 931 GB for a 1 TB drive, you're probably looking at a Windows tool or a utility that counts in binary units. A drive showing far less than either figure may have an extra partition — check Disk Utility → View → Show All Devices.","url":"https://storagestudio.us/faq/mac-storage-basics/why-is-my-external-drive-smaller-than-advertised"}}]},"fragment":"
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Mac storage basics · External storage and adding space

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Why does my new external drive show less space than the box says?

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Short answer: Mac shows decimal units like the box, so a 1 TB drive shows close to 1 TB minus format overhead. Much less suggests binary units in another tool or an extra partition.

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On a Mac, a 1 TB drive should show close to 1 TB, because macOS and drive makers both count in decimal units. A little is used by the format's own structures and, on some drives, hidden partitions.

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If you see a much smaller figure, such as 931 GB for a 1 TB drive, you're probably looking at a Windows tool or a utility that counts in binary units. A drive showing far less than either figure may have an extra partition — check Disk Utility → View → Show All Devices.

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