The standard slide size in Keynote ( version 6.5.2 ) is 1024 x 768 pts.
Wide screen slide size is 1920 x 1080 pts.
You can change the “default” slide size to some other value. To do so follow these steps: Keynote > Preferences > General tab > For New Documents: > Click on “Use theme:” > Click “Choose” > Select “Slide Size” at the bottom. The Slide Size options are available in the Document Inspector.
Standard slides (4:3 aspect ratio) will fill the screen on an iPad. This is a great choice when you know you will be playing your slides directly on the iPad to a small audience or you will be using a projector with a 4:3 aspect ratio. When presented using AirPlay to an Apple TV, these slides will fill the height of the display but not the entire width.
Widescreen slides (16:9 aspect ratio) will fill the width but not the full height of the iPad screen. Choose this size when you will be presenting your slides to a 16:9 video projector or using AirPlay to an Apple TV.
Mac Keywords and paper size in points:
US Letter size paper:
Letter – for 72 PPI
Width & Height: 612 x 792 Pixels (8.5 x 11 inches / 21.6 x 28 cm)
72 dpi monitor viewing: Letter 612×792 px
72 dpi monitor viewing: A4 595×842 px (8.3 x 11.7 inches)
Letter – 300 PPI 2550 x 3300 Pixels
A4 – 300 PPI 2480 x 3508 Pixels
Letter size = Used in Canada and the United States of America.
A4 size = The rest of the world (United Kingdom, Australia, Germany, Turkey etc).
The paper size of A4 paper or Letter size paper in pixels at different Pixels Per Inch (PPI). Each pixel count is in 8 bits of color.
Pixels are not used for measuring size.
One pixel is a small dot of illumination on a display screen.
Multiple pixel dots compose an image.
Pixels are most standardized as 8bit in color in 24bit displays each pixel can achieve over 16 million colors.