Don't leave it up to chance! Use a ring sizer to get the perfect fit. The ring sizer is very easy to use, and can be used over and over.
Thread the ring sizer through its buckle to create a loop.
Place the ring sizer on the finger you intend to wear your gorgeous new ring on.
Pull the sizer to tighten it until you get the right fit. It should be snug, but able to fit over your knuckle. Take it on and off a few times to make sure you're happy with the fit.
Your ring size is the measurement on the inner side of the buckle.