In your FCE exam, all written answers must be between 120 and 180 words. When writing under exam pressure, it is important to count words and not to lose time.
How do you count words?
Here's the trick: train your eye.
By the time you sit for an exam you should know how many words in your handwriting fit a line.
If you must count, do not count word by word. Select two or three lines of your text; count the words on those lines. Obtain the average and then multiply by the total number of lines. Much faster.
On the computer
When you practise for the class, you may use your word processor to do the word count. (Tools>Count Words). There is also a toolbar in some versions of Word that will update the count when you make alterations.
My students are writing on a wiki which does not include a word counter. It is quite uncomfortable to open Word just to cut and paste your sample and check on the total number.
Here are a couple of websites with word counting tools
How many words is too much?
Let's say that 10% more than the total mentioned in the exam rubrics is as far as you can go. If you have written a remarkable piece, a few extra words will not affect your mark.