"The size of the doll and the head is not what needs to be measured. The size of the eye opening is the measurement you need. To do this you need a measurement tool either a ruler, measuring tape, or micrometer. Take the dolls head and measure the eye opening from size to size (corner of the eye near the nose, out toward the ear) once you have gotten that measurement it will need to be converted to millimeters. (see chart below) We usually recommend adding a millimeter or two to that measurement."

Note: I'm also told that manufactured eyes are measured by the size of the iris...which would not include the "whites".    Maybe this only applies to the oval acrylic eyes....I'm not sure....ask your supplier before ordering to make sure you're ordering correct size!

Question: What is the difference between styles?

There are glass and acrylic styles. Some are oval and some are round.  Some are hand blown and are called pinch-back eyes because the glass is pinched together on the back of the eye.  Some eyes have a thread or wire attached to ease installation.  "Safety eyes" have a peg and clip system designed for soft sculptures where a child might try to pull eyes out.

Eyes called 'paperweights' are solid glass and have a slightly raised iris and a completely smooth flat back. Paperweight eyes can vary greatly in price and ease to work with. Many old French Dolls require hi-end Paperweight Eyes to uphold their value.

Any of the eye types or styles can be used with air dry clay.  Make sure they're heat-resistant and can be placed in oven if using with polymer clay.  Glue is frequently used to attach eyes in clay dolls but they can also be held in place with surrounding clay.
Question: What is the difference between a Round and Half Round eye?
Answer: The round eye is similar to a light bulb whereas a half round is like a large contact lens or bowl. (see photo below)

Eye Sizer tools are available. These are individual tools or sets of different sizes.  Used by clay artists to shape holes for dolls eyes.  Each end presents a different size.