Size guide
How a head is measured.
The record is metric. Inches and ounces on a product page are a conversion of that record, not a second measurement.
Measurements on the photos

Bloom 6 cm. Overall length 28 cm. Weight 9.3 g. Leaf 11 cm. Lower stem 16 cm.

Bloom 8 cm. Height 40 cm.

Overall length 65 cm. Bloom 10 cm. Branch 30 cm.
Diameter
Measure the widest petal tip to the petal tip opposite, across the face of the bloom. Do not include a stem. A mixed pack has no single diameter: the note carries the range, and the diameter cell stays empty.
An 8 cm head against a 20 cm line
8 cm / 20 cm
Height
Measure from the base — the glue pad or the calyx — to the top of the bloom. A stem added later is not part of the height.
Layers
Count the bonded layers you can lift apart. Petals sitting in the same layer count as one.
The base
Three kinds show up on a product page: a flat glue pad, a calyx with a locating point, or a socket that can take a stem. The page names the one that style uses. It does not invent a fourth.