I want to make a meal and I need to substitue fresh Thai chillies with cayenne chillies or dried Thai chillies, how much should I add?

I want to make a meal that had fresh Thai chillies crushed in a mortar in the recipe, but I can't buy them where I live. I can buy cayenne chillies or maybe order dried Thai chillies online and use them as a substitue, but don't know how much should I add to get the most similar result. Also would it make a huge difference compared to making it with fresh Thai chillies?

How much of cayenne chillies would equal to one fresh Thai chilli? And I have the same question about the dried Thai chillies. Thanks!