In a gory case of your busybox df “applet” doesn’t have a notion of -i and you still wonder how many inodes occupied/free you can try checking if you’re lucky enough to have tune2fs installed – dumping its output through fgrep -i node you should have your curiosity fully satisfied:

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Inode count:              1441792
Free inodes:              1115832
Inodes per group:         8192
Inode blocks per group:   512
First inode:              11
Inode size:               256
Journal inode:            8
Journal backup:           inode blocks