What You Need for a Custom Google Sheets Template
A Google Sheets custom template contains information specific to the spreadsheet you want to make. To make a custom template, start with a spreadsheet file that contains the information and formatting you want to use in the template. Create the spreadsheet file in any spreadsheet program, such as LibreOffice or Microsoft Excel. You can even make the spreadsheet in Google Sheets, either from scratch or from the Template Gallery. Just open one of those templates and edit it as needed to fit your project.
Make a Folder for Custom Templates
To keep your custom templates organized, create a folder that will contain only template files.
Add Your Template to the Folder
To add your custom template to the newly created folder:
Use Your Custom Templates
When you want to use this custom template to create a new spreadsheet, make a copy of the template file before you make any changes to the original template file. If you edit the original template, you won’t have that unaltered template available for use in the future. To make a copy of a template, right-click or tap-and-hold the template file, then choose Make a copy. Then, rename the copy and move the copy to another folder so that you don’t accidentally edit the template.