The present invention relates to a wet film gauge comprising: a gauge main body from which a gauge wall protrudes; a coating film measuring groove part formed on the gauge wall at different heights; a coupler formed on the bottom of the gauge main body; and a fastening line fastened to the coupler to fasten the hand or finger of a worker by covering it. Therefore, the wet film gauge prevents a coating worker from carelessly losing the gauge main body; and significantly reduces the entire work time for coating as the gauge main body is fastened to one hand of a worker grasping a spray gun with the other hand to enable the worker to rapidly measure coating thickness.
