What sizes of designs are needed for an adaptive layout of an online store?

Question

Adaptive design

We are designing. What sizes of designs are needed for an adaptive layout of an online store?
1. They advise different:
320, 480, 768 and 1170
320 768 992 1170
2. They also offer to reduce it to, they say, this is enough for a competent layout designer:
320 768 and 1170
What sizes are correct?

Answer 1

Pay no attention to the final dimensions. Think devices.
1. Smartphones that are held vertically (it doesn’t matter if it’s an iPhone 4 or an iPhone 6 plus or maybe a Galaxy Age) (usually 300-450)
2. Smartphones that are held horizontally (again, any) (usually 450-600)
3. Tablets in vertical (typically 600-800)
4. Tablets in landscape (typically 900-1024)
5. Desktop screens (1024+)
6. Very large screens (1600+)
So, as you can see, final sizes can jump depending on type of smartphone, so the design should be a little rubbery within each step.