MDPI is your baseline. Means the base size, which is ~160dpi. Every other density qualifier is calculated based on the baseline
HDPI is 1.5*MDPI
XHDPI is 2*MPDI
XXHDPI is 3*MDPI
XXXHDPI is 4*MDPI
Or, see this table for a better description
| Density Qualifier | Factor | DPI | Description |
|-------------------|------------------------|------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| ldpi | MDPI / 1.33 | ~120 | Resources for low-density (ldpi) screens (~120dpi). |
| mdpi | MDPI * 1 | ~160 | Resources for medium-density (mdpi) screens (~160dpi). (This is the baseline density.) |
| hdpi | MDPI * 1.5 | ~240 | Resources for high-density (hdpi) screens (~240dpi). |
| xhdpi | MDPI * 2 | ~320 | Resources for extra-high-density (xhdpi) screens (~320dpi). |
| xxhdpi | MDPI * 3 | ~480 | Resources for extra-extra-high-density (xxhdpi) screens (~480dpi). |
| xxxhdpi | MDPI * 4 | ~640 | Resources for extra-extra-extra-high-density (xxxhdpi) uses (~640dpi). |
| nodpi | See description | n/a | Resources for all densities. These are density-independent resources. The system does not scale resources tagged with this qualifier, regardless of the current screen's density. |
| tvdpi | Recommended: MDPI*1.33 | ~213 | Resources for screens somewhere between mdpi and hdpi; approximately 213dpi. This is not considered a "primary" density group. It is mostly intended for televisions and most apps shouldn't need it—providing mdpi and hdpi resources is sufficient for most apps and the system will scale them as appropriate. If you find it necessary to provide tvdpi resources, you should size them at a factor of 1.33*mdpi. For example, a 100px x 100px image for mdpi screens should be 133px x 133px for tvdpi. |
See this image for more information
Source: https://developer.android.com/training/multiscreen/screendensities