Blue sizers: Just pop out and try on to find your perfect fit! Sizes are marked on the little tabs. Very easy to use.
Zip tie: works like a belt, instructions included.
2 1/2 to 14 in US/Canadian sizing with the Blue plastic sizers. and sizes 1 to 17 with the zip tie sizer.
Note: all plastic ring sizers are bit off (~1/4 size up or down tolerance) and not as accurate as calibrated metal sizer. It's always a good idea to get sized by a professional jeweler.
Use with this tool to convert to international sizes.
Here are a few steps to make your measurement more accurate:
When measuring, keep in mind that each finger could have a different size, so don't presume that a ring that fits your left ring finger will also fit your right ring finger.
Measure when your hands are warm, not cold.
Make sure the measurement you choose easily fits over your knuckle.
For wide rings you may need to order 1/4 to 1/2 size larger than you normally wear.
For more ring sizing information and helpful tips see this page.