Tips: Remove any line breaks from your Word document. When the universities view your personal statement, they will be viewing it as one large chunk anyway. Just because you have less than 4000 characters doesn't always guarantee that you are less than 47 lines. Also, I would say leave 30-50 characters to spare after you have finished a draft. Copy and paste this draft onto the UCAS form and it will then format it and tell you how many characters you are under/over.
The number of characters on a line vary from device to device so I find the only way to actually find out how many characters it is will be to paste it on the form itself. Also, each line is a character so make sure you account for this too.