HDPI refers to a high-density screen (about 240 dpi) used on an Android device.
MDPI refers to a medium-density screen (about 160 dpi) used on an Android device.
Computer monitor resources
"Example if using dp unit hdpi device will have 1.5 240 160 times larger than mdpi"
from question "Having problems with using dp and sp on different densities"
"And you know your image at hdpi folder so its 1.5 larger than the mdpi"
from question "Calculate drawable width"
"For example mdpi is basically 72dpi as your computer monitor hdpi resources should be around 1.5 times larger than mdpi resources and so forth"
from question "Android resolution always using x-large drawables in any device"
"As mdpi is less than hdpi so it will take the values from the folder which is least below it in you case it is values which is applicable to all"
from question "Which folder will the element receive the params? (Android)"
"Ideally the hdpi version of your button should be 1.5 times bigger than the mdpi baseline version"
from question "How to handle xml UI for diffrent-2 screen resolution android"
Pixel sizes smaller
"Layout-sw320dp-land will pick up drawable from hdpi folder whereas layout-sw720dp-land is mdpi device so it will pick up drawables from mdpi folder which will be smaller than hdpi"
from question "Design drawables to maintain proportions in all devices"
"When you put images into hdpi folder their appearance is smaller than from mdpi and ldpi"
from question "How to improve the image quality when images are in drawable folder"
"Images in these different folders should have different physical pixel sizes mdpi has smaller images than hdpi but the images pixel densities aren t used"
from question "Windows and BlackBerry icon size and pixel density"
"Ldpi assets will look bad on high density screens but are exponentially smaller than mdpi which is exponentially smaller than hdpi etc"
from question "Android apk size less than 20kb"
"The system will pick the closest match and mdpi is closer to hdpi than to xxhdpi"
from question "Using hdpi drawables in mdpi tablets without creating image copies"
"First of all if you anyhow provide a hdpi graphic adding an mdpi and ldpi graphic which both are less than the hdpi graphic in size there is approximately 3 4 6 scaling ratio will increase the size but far from triple it more close to double"
from question "Android: Why create specific images for ldpi, mdpi and hdpi?"