R.I. Gen. Laws § 5-83-7: Measurement of propane for sales purposes.

(a) Propane supplied to portable containers shall be measured and billed by weight, before and after filling, as shown on a national type evaluation program scale.

(b) Propane supplied to portable containers that cannot be weighed shall be measured by a national type evaluation program approved meter.

(c) The price per unit weight, or gallon, shall be conspicuously posted at the site of the filling scale.

(d) This section shall not apply to propane tank exchange programs wherein prefilled portable propane containers are provided to consumers for a flat fee.