One of the most significant major differences between the Apple Watch 3 & Apple Watch 4 is the scale of the physique, as whereas the Apple Watch 4 comes in a selection of 40mm or 44mm, the Apple Watch 3 is out there in a choice of 38mm or 42mm. The 40mm Apple Watch 4 has a bigger display space than the 42mm Apple Watch 3. Apple watch series 4 44mm is a great watch and a must-buy if you have an iPhone.