Which size lens would fit the lens kit that comes with the sony a7iii (fe 28-70mm f/3.5-5.6 oss lens)?
55mm, but if I was you I would get a bigger filter and use step down rings to fit the size you need. Like the Tamron lenses are 67mm other nice Sony are 67mm & 82mm so I would get 82mm and use step down rings. That’s just me
Sony's website indicates that it has a 55mm filter thread. For this and any lens, you can find this information on the manufacturer's website, on retail websites, or by reading the front of the lens.