As you can see from the above screenshot, the size of the PBIX file is 1.2 MB (1,238 KB) by looking at the size in file explorer. Also, when we look at all the files we are ingesting into Power BI, the total size comes to 2.8 MB. However, when we ingest data into Power BI which is processed to memory, it can be bigger than the PBIX file size due to some compression that occurs and various other elements which again, are not displayed through the disk.
So, when we are getting various errors notifying us that our Power BI file is too large and we see that it is under the 1GB restriction on disk, it can leave us scratching our head. But, as I mentioned above due to compression and various other elements, once data is processed to memory it can be larger then what we see on disk, but still below the total size of the data source we are ingesting due to the compression.
Click through for information on two tools you can use to determine the in-use size.