Using an invoice template in Google Docs
Google Docs is a good fit for invoicing if you send a handful of invoices a month and want everything in Google Drive. You download the Word version of this template, open it with Google Docs, and keep it as your master. Each invoice is a copy of that master, saved as a PDF before you send it.
Google Docs tables don’t calculate totals. If you want amounts and tax worked out for you, use the Excel version in Google Sheets instead (the steps are below). The full template, with a guide to every field, is on the free invoice template page.