How do I crop an excel text cell to 250 character

How do I crop an excel text cell to 250 character

I have text stored in microsoft excel 2010 text cells which I need to crop
to 250 characters rounded up or down to the nearest full word.
So for example the text
A lot of text ........ which ends like this
lets say the 250th character is the "i" in "like" I'd want the cell to
convert to
A lot of text ........ which ends like
I hope I've made my self clear.
Many Thanks
Nigel