URL format

Browser URL

https://docs.google.com/spreadsheets/d/{KEY}/edit?gid={GID}#gid={GID}

Export URL

https://docs.google.com/spreadsheets/d/{KEY}/export?gid={GID}&format={FORMAT}

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Downloadable format

CSV: current sheet

https://docs.google.com/spreadsheets/d/{KEY}/export?gid={GID}&format=csv

TSV: current sheet

https://docs.google.com/spreadsheets/d/{KEY}/export?gid={GID}&format=tsv

Microsoft Excel: all sheets

https://docs.google.com/spreadsheets/d/{KEY}/export?gid={GID}&format=xlsx

OpenDocument: all sheets

https://docs.google.com/spreadsheets/d/{KEY}/export?gid={GID}&format=ods