Calculating the Pixels Per Unit (PPU) for a Background in Unity

Objective: To show you how to calculate the correct Pixels Per Unit (PPU) for your 2D games background in Unity.

Our beautiful space background

How many times have you simply dragged a sprite asset into your project for it to be massive and you might play around with the PPU a little bit till it feels right and then you adjust the scale or size of the object, or had to adjust the main camera’s transform when you didn’t want to move it? Many times. So let’s see how a simple calculation can make your life a lot easier!

PPU refers to how many pixels you would like to display unit to unit. The Space Shooting game I am creating is designed for HD 1920 x 1080 (16:9 ratio). The sprite background that I have imported into my game already has the required pixel width and height (1920 x 1080) which makes things a little easier however, when importing the asset it still comes through as 100 PPU which isn’t correct (so we need to fix this).

We are also going to need the camera size that you have setup for the game. The standard camera size will start as 5 and I have left mine as this.

Camera Size
Pivot Point

Now, when you drag the sprite background into the Hierarchy it will automatically be in the scene and the pivot point of the image will be in the centre and we can consider this to have the coordinates of (0, 0) on the X and Y axis respectively. Using the coordinates starting point of (0, 0) and the camera’s size of 5, we now know that the total height of the camera is 10 (5 * 2).

Total camera height

Now, we can make our calculation by dividing the Y axis height of the image (1080) by the total height of the camera size (10):

                          1080/10 = 108. 

So our background sprite should have the PPU set as 108.

This first image is the original 100 PPU when imported into our game (notice that the full background seems a bit zoomed in and isn’t showing all the stars, some are missing as this is only displaying 100 pixels per unit = 1000 total, so 80 pixels are missing!):

100 PPU

Now with the correct PPU: 108 (displaying 108 pixels per unit * 10 units total = 1080!):

108 PPU

And, you can also see that we haven’t had to change a single setting for the main camera or backgrounds transform position or scale!

Main Camera transform
Space Background transform

A simple calculation and we have an image that fits perfectly!

Useful Links
https://docs.unity3d.com/ScriptReference/Sprite-pixelsPerUnit.html
https://docs.unity3d.com/ScriptReference/Camera-orthographicSize.html

Aspiring Unity Game Developer with a passion for bringing code to life!