Using the TI CellSheet Converter utility provided by Texas Instruments, it should be possible to transfer simple spreadsheets saved in Microsoft Excel format (.xls, .xlsx) to your TI device, including TI-NSpire. For other graphics calculators, the utility will convert it to other format suitable on that specific device.
Convert Microsoft Excel 97 to 2003 workbook to TI-Nspire document.
We found one software available in the database for this conversion.
Microsoft Windows software - convert xls to tns on Windows
A converter for transfer spreadsheets to TI calculators
Convert from xls file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.