R.I. Gen. Laws § 44-5-13
The assessors shall assess all valuation and apportion any tax levy on the inhabitants of the city or town and the ratable property in the city or town according to law, and the assessed valuation of the ratable property shall be made as of the date of assessment provided in § 44-5-1 and shall be in accordance with the provisions of § 44-5-12; except that personal property consisting of stocks in trade and materials used in manufacture, which include raw materials, fuel, goods in process of manufacture, and completed products, except those which are specifically exempt by statute, are estimated at the average of the personalty kept on hand or located in the taxing district during the twelve (12) months ending with the date of assessment, or the average of any portion of the twelve (12) months when the business has not been carried on or located in the taxing district for a year.
R.I. Gen. Laws § 44-5-13