The only rule is that you will automatically lose points if your responses are below 150 and 250 words. But generally these are good guidelines and I would aim for 150-170 for part 1 and 250-280 for part 2. If you write much more than this, it's likely that there will be some repetition or not very relevant information. The key is to use language structures that allow you to organise your thoughts more coherently, and to pack more information into fewer words. These aspects of the test give access to the higher bands and are essentially why the suggested upper limits are there.

Dear David, There is no "ideal" word count for IELTS writing tasks. However, you need to bear a few things in mind when approaching either of the tasks. In task 1, for General training, you need to make sure that each bullet point is sufficiently developed. In the academic module, you need to make sure that you have covered the key features of the task without getting into the details too much. I would say that an effective task 1 response will be in about 220 or so words. However, this is not a rule set in stone. As for task 2 (the essay), you should make sure that you develop the main ideas in the prompt to a reasonable degree. Here, you can include examples from personal experience / knowledge. Your own ideas should also be clearly communicated. I would say that a sufficient task 2 response would land somewhere around 300 or so words. That said, you should keep in mind that the longer your response, the higher the possibility of making mistakes. Also, you will want to end up with 5-7 minutes of spare time to review and improve your response. I hope this helps :)