Why does Windows show 13 GB of RAM in use when my processes only add up to about 8 GB?

The Processes tab doesn’t represent every category of memory. The total in the Performance tab can also include Windows itself, cached or standby data, memory compression, kernel and driver allocations, shared memory, and hardware-reserved memory. Windows will normally reuse cached RAM when an application needs it, so high usage by itself isn’t necessarily a problem. Check the Memory details in Resource Monitor or use Microsoft RAMMap if you want to see which category accounts for the difference.

Make sure you’re comparing the right figures. The Processes tab may show a process’s working set, while the Performance page reports overall physical memory usage. Those numbers will not add up exactly because system services, the kernel, drivers, compressed memory, and cached pages are reported separately. If the computer is actually paging heavily or becoming sluggish, check the Committed and Available values rather than focusing only on the percentage.

Chrome can definitely use several gigabytes with many tabs, extensions, and separate renderer processes, but it shouldn’t automatically explain all of the discrepancy. Try closing Chrome completely and compare the Memory percentage afterward. You can also boot into Safe Mode or perform a clean startup; if memory usage is much lower there, a background application or driver is likely involved.