It depends on the hardware, for example, mine D-Link DIR-320 (A) has 32MB of RAM and 4MB of ROM (3801599 bytes, to be precise). It's not enough to fit last kernel (IIRC 4.8 for OpenWRT) even without GUI, I had compile it with some hacks.
Edit. It has 256MB of RAM, 128MB of ROM. There is no excuse for this.
It depends on the hardware, for example, mine D-Link DIR-320 (A) has 32MB of RAM and 4MB of ROM (3801599 bytes, to be precise). It's not enough to fit last kernel (IIRC 4.8 for OpenWRT) even without GUI, I had compile it with some hacks.
Edit. It has 256MB of RAM, 128MB of ROM. There is no excuse for this.
https://openwrt.org/toh/netgear/r7000