Storage Usage Viewer
Figures come straight from your browser's own storage gauge; the reading happens on your device and nothing is sent anywhere.
How it works
仕組みHow much space is this browser allowed to use on your device, and how much of it is already spoken for? One press reads your browser’s own storage gauge: bytes used, the total quota it will allow, and, in Chromium browsers, a breakdown of where the bytes sit, from cached files to IndexedDB. You also get a count of this site’s localStorage and sessionStorage entries and whether your storage is marked persistent or best-effort. The numbers are unique to your browser profile and disk, so only a reading taken on your own machine means anything.
Browsers typically offer each site a generous slice of free disk: Chromium allows up to about 60% of the whole disk per origin, and Firefox similar per group of sites. The quota is a ceiling, not a reservation: nothing is used until a site actually stores data, which is why usage is usually a tiny fraction of quota.
Best-effort storage (the default) can be evicted by the browser when the disk runs low, starting with sites you visit least. Persistent storage survives that cleanup and is only removed when you clear it yourself. Sites must request persistence, and browsers often grant it silently only to sites you use heavily or have installed.
The per-category usageDetails field is a non-standard Chromium extra, so Chrome and Edge show it while Firefox and Safari report only the total. Safari is also the outlier on quota, historically capping origins around 1 GB unless the site is saved to the home screen. The totals are still accurate everywhere the Storage API exists.