Tidy MacHow much storage does my Mac need?
Add up what you keep on the Mac itself, add room for macOS, then leave about a fifth of the disk free. Move the sliders below; every size assumption is shown and editable.
Estimates from your inputs and the assumptions shown. The macOS and System Data figure starts at a rough 60 GB; System Data varies a lot between Macs, so set your own.
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How it works
Each row is amount × typical size. The typical sizes are assumptions, not measurements: change them to match your camera, your games or your models. The total adds your estimate for macOS and System Data, then divides by (1 − free space you want to keep), and picks the smallest of 256 GB, 512 GB, 1 TB, 2 TB that fits.
Storage sold as 512 GB is 512 decimal GB, the same units Finder uses (see the GB to GiB converter). Developer and AI workloads are usually the biggest surprise: read about Xcode DerivedData and local AI models.
Questions
Is 256 GB enough for a Mac?
For web, email, documents and photos kept mostly in iCloud, often yes. Once you keep a large photo or video library on the Mac, install big games, use Xcode or run local AI models, it fills quickly. Move the sliders to see where your own use lands.
Where do the per-item sizes come from?
They are rough, typical assumptions for illustration, not measurements, and every one is editable. Photo, video and model sizes vary a lot with camera, resolution and format. If you have a Mac now, check real sizes in System Settings › General › Storage and enter those.
Why leave free space?
macOS needs room for updates, swap, caches and Time Machine snapshots, and System Data grows over time. A Mac that runs nearly full is the most common reason people search for Mac storage full. The calculator keeps 20% free by default; change it if you like.
Can I use iCloud or an external drive instead?
Yes. Optimise Mac Storage keeps only recent photos and files on the Mac, and big libraries can live on an external SSD. Set those sliders to what you keep on the Mac itself.