If you have a large data file and want to know how many rows it has, command line is a quick way to do that.
On Mac/Linux the relevant command is wc (think 'word count'); on Windows PowerShell it is Measure-Object
Using wc is relatively easy: use other commands to navigate to the folder containing your file, then type wc followed by the filename, e.g. wc myfile.csv. You should get a result which shows lines, words and characters in that order.
This command is more complex, as it has to be combined with others. Here's an example:
Get-Content yourfilename.csv | Measure-Object -Line
This code first gets the content (make sure you have navigated to the folder containing that file), then runs Measure-Content and specifies that it wants to measure the lines.