You can check your iCloud storage on the iOS platform, but if you’re using a Windows machine you can check it on the desktop as well.
However, you’ll need to have the iCloud dashboard installed on your computer first.
To check your storage, head to the Control Panel, and then choose the “iCloud” option. That’ll bring up the iCloud menu.
There, you’ll be able to choose what data is being backed up to iCloud, and it’ll also show you a graphical representation of your free storage – you can also choose to show the iCloud dashboard in the system tray.