It depends on what resolution your monitor is, assuming you don't want to run at a lower resolution than your screen. You'll get away with 4GB for up to 2560x1440. I wouldn't like to go any lower than that for 1440p. You may get away with less for 1080p though. The stated minimum is 1GB, but hardly anything made in the last 10 years will have such a small amount of VRAM, except cheaper laptops. The recommended is 4GB.
Even at 4K with everything turn up to 11 I’ve not seen it go above 5gb. Bear in mind however, if and when this DX12 change comes the chances are the VRAM requirement will increase. If you even a remotely modern card though you’ll be fine.
