A useful summary of Google Docs, Spreadsheets and Presentation size limits to bear in mind when uploading and converting.
Up to 1.02 million characters, regardless of the number of pages or font size. If you convert a text document to Google Docs format, it can be up to 50 MB.
5,000,000 cells, with a maximum of 256 columns per sheet. Uploaded spreadsheet files that are converted to the Google spreadsheets format can’t be larger than 20 MB, and need to be under 400,000 cells and 256 columns per sheet.
Presentations created in Google Slides can be up to 100 MB for presentations converted to Google Slides.
Files that you upload but don't convert to a Google format can be up to 5 TB each, so you can upload very large files such as videos and high resolution artwork with no problem - as long as you have the storage (Business users get 30GB of free storage across Gmail and Drive; personal users have 15GB - both can purchase additional storage). Files converted to the Google format are "free" - ie they don't take up any storage space.