Sorry the sizes below relate to my old theme. I have to readjust them for the Twenty Sixteen theme I now use.
Current Maximum Width Screen Sizes
All Screens
Site Width: 1305px
Header Width: 1305px
Header Height: ?px
Menu Bar, etc. Width: ?px
Menu Bar, etc. Height: ?px
Sub Menu Items, Width: 200px
Sub Menu Items, Height: 36px
Go To Top Icon: 48px x 48px
Featured Images
Width: ?px
Height: ?px
Aspect Ratio W:H =?
Blog Posts
Content Width: 600px
Maximum Image Width: 600px
Maximum Image Height: 1100px
Left Margin: 111px
Text Width: 672px
Right Margin: 111px
Right Border: black 1px within right margin
Video Width: 672px
Video Height for Aspect Ratio 4:3 : 504px
Video Height for Aspect Ration 16:9 : 378px
Content Sidebar Width: 366px
Left Margin: 15px
Widget Width: 336px = 672 ÷ 2
Right Margin: 15px
Variable Full Width Pages
Left Margin: 30px
Text Width Max: 1200px
Right Margin: 30px
Fixed Full Width Pages
Left Margin: 30px
Text Width: 1200px
Right Margin: 30px