.WK1 File Extension

Spreadsheet created by Lotus 1-2-3, a popular spreadsheet program in the 1990s; contains cells, which are organized by rows and columns; used to store and analyze structured data, as well as quickly compute formulas.

Lotus 1-2-3 is included with Lotus SmartSuite, which was acquired by IBM in 1995.

NOTE: WK1 files can be opened in some versions of Microsoft Excel. However, some formatting information may be lost during conversion. WK1 files are no longer supported by Excel 2007 and later.