If getting a professional measurement from a Jeweller is not an option for you, there are a couple of alternatives to getting your ring size.
Before you take any finger measurements, hands must not be to warm or too hot, as fingers can shrink or expand. Normal body temperature is good.
The first method is to take a thin strip of paper or non-stretchy string about 6 inches long. Wrap it around the base of your finger. Make sure it’s a snug fit but not too tight. Mark the point of overlap on the string/paper. Compare this measurement to a ring size chart which you can find online. Or simply message me your measurements and I will work it out for you. If you find that you are between sizes then order the larger size as fingers swell in heat and cold.
If your knuckle is much larger than your finger’s base, take two separate measurements and choose a size in between. You want a ring to fit over your knuckle, but not to be too loose or it will shift around.
Alternatively measure the inside of your own ring and match it to the size guide on the chart. Again, if you are between sizes then order up.
These suggestions are a rough guide only. For a professional measurement please get sized in a local jewellery store.