There have been conflicting reports of whether projects are limited to 50 MB, but Scratch Team member Za-Chary has confirmed:
|“||You can make projects larger than 50 MB total||”|
– Za-Chary, 
In Scratch 3.0, all assets must be under 10 MB, and the project JSON must be under 5 MB. There is no explicit limit on project filesize, but with the (otherwise) smallest possible project containing as many assets as possible, the largest a project can be while remaining within the explicit limits is 318 GB.
|“||We used to be stuck with the 10 megabyte limit due to limitations in Java. We hope to be able to extend this limit in the next version of Scratch - but server space costs $! Unlimited is too big, 10 MB is too little.||”|
– Lightnin, a former Scratch Team member
The Scratch 2.0 File Format uses a more efficient storage system than the 1.4 file format, so projects took up less space than before. The limit on total project size in Scratch 2.0 was 50 MB, 5 times the 10 MB limit in Scratch 1.4, although projects uploaded from the 1.4 editor were still limited to the previous 10 MB. However, each individual "asset" (sound/image) must be 10 MB or less.
Not many projects get close to the limit, but some have came close.
How to tell when a Scratch 1.4 project is too big
|This article or section documents something not included in the current version of Scratch (3.0). It is only useful from a historical perspective.|
How to tell when a Scratch 2.0 project is too big
If one is offline, then the user will know when they try to upload their project to the Scratch Website; Scratch will display this generic error message when the file is too big to upload:
If the user is on the website, though, they'll know when their project is too large when they cannot add any more costumes, sounds, backdrops, or anything to it.
Reducing Project Size
- Main article: Project Compression
The best way to reduce the size of a project is to compress the sounds and images. Below are some tips:
- Delete all sprites and scripts which are not used
- Delete variables and lists which are unused
- Use stamping and cloning instead of lots of sprites when possible
- Delete all sound files that are not used, as they take up a lot of space
- Use custom blocks to reduce script sizes
- Use vector graphics instead of bitmap graphics (especially for simple costumes like circles and boxes)
- Use lower quality images and sounds with lower file sizes
- Kenny2scratch. (12/3/2019). "318,155,249,999 bytes (318 GB) is the maximum size for a project." post:3870217