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---
title: Display density on Android
language: en
layout: default
created: 2015-12-02 17:19:42 +0200
updated: 2015-12-02 17:19:42 +0200
toc: false
tags:
- know-how
- hacking
- android
- display
- resolution
- lcd
---
Methods
=======
Android supports changing the display resolution in 2 different ways.
wm density
----------
This method works without root and changes the density of the *window manager*.
You can call this command only from the adb shell.
The syntax is:
wm density [ppi]
E.g. the Nexus 9 has a real display density of 288ppi, so you would run:
wm density 288
To reset the value to the factory setting (for the N9 that is 320), just run:
wm density reset
build.prop
----------
The other way to change the display density is to edit the `build.prop`. This
only works with root access.
To edit the file, first make the `system` partition writable by remounting it.
Then find the file `/system/build.prop` and open it in a text editor. I use
my favourite file manager [FX File Explorer](https://play.google.com/store/apps/details?id=nextapp.fx)
with its integrated editor for that.
Find the following line (Example from Nexus 9 with currently 320ppi):
ro.sf.lcd_density=320
And change the number to your desired value. BE SURE TO NOT CHANGE ANYTHING ELSE.
Save the file and reboot your device.
Advantages
==========
Setting the correct density value makes the display appear sharper and it may
even make your device run better.
Android knows different *densities* and if an app supplies graphics in different
qualities, it loads them according to the detected density. This means: The
higher the density, the larger graphics Android has to load and keep in
memory. So reducing the density (to the real value) can make Android load
a bit less detailed graphics and thus save RAM.
Android knows these quality classes:
| Class | PPI |
|------:|:-------:|
| ldpi | 100-140 |
| mdpi | 141-199 |
| hdpi | 200-319 |
| xhdpi | 320-340 |
| xxhdpi| ~480 |
|xxxhdpi| ~640 |
As you can see, the 320ppi of the Nexus 9 makes Android use *xhdpi* resources.
If you change the density to 318, you won't notice anything, but Android will
suddenly use the *hdpi* resources and save memory when running apps.
Problems
========
If you don't have root access and try to change the density using the `wm density`
command only, it might seem to work on the first glance, but you will notice
strange effects.
If you're using SwiftKey, you'll notice it right away:
![]({{ site.url }}/assets/android-dpichanged-swiftkey-broken.png)
Other problems are more subtle (Nexus 9 at 288ppi):
![]({{ site.url }}/assets/android-dpichanged.png)
Compare this to the same screen at the original 320ppi:
![]({{ site.url }}/assets/android-originaldpi.png)
(If you're still searching: Notice the huge "chevron" icon after the
developer's name. And also the **huge** background image.)
<p><div class="noteimportant" markdown="1">
These problems only occur if you use only one method to change the density. If
you use **both** methods and set them to the same value, everything will look
just fine.
</div></p>
More info at the [xda forum](http://forum.xda-developers.com/nexus-9/general/guide-little-trick-improvimg-nexus-9-t3224931).