Am getting on great with my first ever dildo (3cm circumference), but when I am ready for a larger one how much do I increase the circumference by. Half a cm, one cm or what? I don't want to buy one then find I would have been able to manage a bigger one.
I guess that would depend on what you think you can handle! If the 3cm is easy for you now then maybe go up a cm? If it can still be a struggle then go half.
You can always work up to a bigger one by using the one you have now beforehand to warm up with.