On Windows, open Settings > System > About and look for Installed RAM
On Windows, press Ctrl + Shift + Esc, open Task Manager, and check Performance > Memory
On Windows, press Win + R, type msinfo32, and check Installed Physical Memory
On Mac, click the Apple menu > About This Mac and check Memory
On Linux, open a terminal and run free -h
On Linux, run cat /proc/meminfo and check MemTotal
On Linux, run sudo dmidecode -t memory if available
On Chromebook, open Settings > About ChromeOS > Diagnostics
On Android, go to Settings > About phone and look for RAM
On iPhone, check the device model specifications online, since iOS does not show RAM directly in Settings