Resolution confused me until I investigated the units behind it.

Takeaways

Units: resolution

Unit Definition Measures
dot device pixel length
px CSS pixel length
cm CSS centimeter length
in CSS inch length
dppx dots/px resolution
dpcm dots/cm resolution
dpi dots/in resolution

Outputs from res

Method Output (current device) Unit
res.dppx() ? dppx
res.dpi() ? dpi
res.dpcm() ? dpcm

Relevant JavaScript natives

Input Output (current device) Notes
window.devicePixelRatio ? draft, quirks
window.matchMedia ? standard
window.msMatchMedia ? IE10 PP3
window.screen.deviceXDPI ? IE, zoom-relative
window.screen.deviceYDPI ? IE, zoom-relative
window.screen.logicalXDPI ? IE
window.screen.logicalYDPI ? IE
window.screen.systemXDPI ? IE
window.screen.systemYDPI ? IE

devicePixelRatio

Relevant JavaScript modules