What is a gloss unit ?

The measurement scale, Gloss Units (GU), of gloss meters is a scaling based on a highly polished reference black glass standard with a defined refractive index having a specular reflectance of 100GU at the specified angle.

This standard is used to establish an upper point calibration of 100 with the lower end point established at 0 on a perfectly matt surface. This scaling is suitable for most non-metallic coatings and materials (paints and plastics) as they generally fall within this range.

Gloss meter calibration tile GU gloss unit value

For other materials, highly reflective in appearance (mirrors, plated / raw metal components), higher values can be achieved reaching 2000 Gloss Units when measured at 20°.

More information the theory of gloss meters is available here: