Yes, METRICS is a Scrabble word!

Letter values in Scrabble US: M 3, E 1, T 1, R 1, I 1, C 3, S 1.

Is it a valid word?

METRICS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

the study of poetic meter and the art of versification
a function of a topological space that gives, for any two points in the space, a value equal to the distance between them
a decimal unit of measurement of the metric system (based on meters and kilograms and seconds)
a system of related measures that facilitates the quantification of some particular characteristic

Also: metric function, metric unit, system of measurement.