How is the dataset size measured?

[hansbogert]

When looking at the size of the Rankings table, the website/docs say it is 6.38GB, however it seems it is more in the range of 5.2GB when looking at the on disk size as well as Spark's reported size.
The format I downloaded was the txt-format, which I expected would be close to the reported 6.38GB since there is no compression.