OS Details

Apple Watch 40mm Series 6 has been launched in September 2019.
Apple Watch 40mm Series 6 have watchOS 7.0

Screen Dimensions

Apple Watch 40mm Series 6 screen size is 1.57 inch with ~ 57.0% body ratio of actual device size. Physical dimensions for Apple Watch 40mm Series 6 device is 1.57 x 1.34 x 0.41 INCH or ( 40 x 34 x 10.4 MM).

Displaying of Units are in this order "Height x Width x Thickness"

Screen Pixel Density and CSS Pixel Ratio

"Pixel" is smallest unit/element of any display.

The total number of pixels that fit into an inch is referred to as "Screen Density" or "Pixel Density" and it measured as "Pixels Per Inch".
Pixel Desnsity have limits to display Pixels Per Inch depends on different screen sizes. When number of pixels per inch increases than it's screen-size limit, the Display resolution will increase but actual device width/height in pixels remain same. Actual device pixels are known as Device Independent Pixels or CSS Pixel Ratio.

Apple Watch 40mm Series 6 resolution is 394 x 324 ^PX with ~ 326 pixel desnsity.
Apple Watch 40mm Series 6 viewport size is 197 x 162 ^PX with ~ 163 actual pixel density, which means it have 2.0 xhdpi display pixel density.

Screen Resolution and Viewport

The sum of pixels which are displaying on a device is called as "Screen Resolution". and sum of actual pixels of any device is reffered to as "Viewport".

Apple Watch 40mm Series 6 have 1.57" physical screen size and its resolution is about 394 x 324 Pixels with approximately 326 PPI pixel density. Apple Watch 40mm Series 6 has viewport size 197 x 162 Pixels and its pixel ratio is about 2.0.

For better understanding screen actual sizes, viewport sizes, display resolution and about their density click here.

CSS Media Queries

Apple Watch 40mm Series 6 css media queries will help developers to write styles specifically for Apple Watch 40mm Series 6. Here are details:

Apple Watch 40mm Series 6 Media Queries (In terms of Mobile only)

@media only screen and (min-width: 197px) and (max-width: 767px) { /* Your Styles... */ }

Apple Watch 40mm Series 6 Min-Width Media Queries

@media only screen and (min-width: 197px) { /* Your Styles... */ }

Apple Watch 40mm Series 6 Min-Height Media Queries

@media only screen and (min-height: 162px) { /* Your Styles... */ }

Apple Watch 40mm Series 6 Landscape Media Queries

@media only screen and (min-width: 162px) and (orientation: landscape) { /* Your Styles... */ }

Apple Watch 40mm Series 6 Portrait Media Queries

@media only screen and (min-width: 197px) and (orientation: portrait) { /* Your Styles... */ }

Apple Watch 40mm Series 6 Device Width Media Queries

@media only screen and (min-device-width: 197px) and (orientation: portrait) { /* Your Styles... */ }
@media only screen and (min-device-width: 162px) and (orientation: landscape) { /* Your Styles... */ }

Apple Watch 40mm Series 6 Retina Media Queries

@media
  only screen and (-webkit-min-device-pixel-ratio: 2.0),
  only screen and (   min--moz-device-pixel-ratio: 2.0),
  only screen and (     -o-min-device-pixel-ratio: 2.0/1),
  only screen and (        min-device-pixel-ratio: 2.0),
  only screen and (                min-resolution: 326dpi),
  only screen and (                min-resolution: 2.0dppx) { 
    /* Retina styles here */
}
                                

Retina is actually based upon device pixel ratio. Devices mostly have 2x or 3x display so you can use general retina media queries to display high resolution content on all kind of devices. Retina 2x and Retina 3x media queries given below:

Retina 2x Media Query (for all 2x resolution supported devices)

@media
  only screen and (-webkit-min-device-pixel-ratio: 2),
  only screen and (   min--moz-device-pixel-ratio: 2),
  only screen and (     -o-min-device-pixel-ratio: 2/1),
  only screen and (        min-device-pixel-ratio: 2),
  only screen and (                min-resolution: 192dpi),
  only screen and (                min-resolution: 2dppx) { 
    /* Retina styles here */
}
                                

Retina 3x Media Query (for all 3x resolution supported devices)

@media
  only screen and (-webkit-min-device-pixel-ratio: 3),
  only screen and (   min--moz-device-pixel-ratio: 3),
  only screen and (     -o-min-device-pixel-ratio: 3/1),
  only screen and (        min-device-pixel-ratio: 3),
  only screen and (                min-resolution: 384dpi),
  only screen and (                min-resolution: 3dppx) { 
    /* Retina styles here */
}
                                

Apple Watch 40mm Series 6 Specifications

• Launch Date September 2019
• watchOS 7.0
• Physical Screen Size 1.57 INCH
• Resolution 394 x 324 PX
• Viewport Size 197 x 162 PX
• Pixel Density 326 PPI
• Device-Independent Pixels 163 PPI
• Pixel Ratio 2.0 xhdpi
• Width 394 PX
• Height 324 PX
• Device Width 197 PX
• Device Height 162 PX
• Dimensions 40 x 34 x 10.4 mm (1.57 x 1.34 x 0.41 in)
• Weight 39.7 g - 1.41 oz