Try this finger sizing tool to help determine your ring size. Cut a slit along the top line and wrap it around your finger pushing the pointed end through the slit and measuring the size there. Remember that the ring will need to be snug but will need to fit over the largest part of your finger.
Use the circles in the PDF to judge sizes against your existing rings. Make sure you line the circles up below with the inside of your band to get an idea of size.
Please ensure that you are printing at 100% when printing this page and it is not being shrunk to fit on the page.