VPDS102000 | Vaping Products Duty and Vaping Duty Stamps: Duty Points & Payment: Measuring volume for duty calculations
From HM Revenue & Customs · Vaping Products Duty and Vaping Duty Stamps guidance
When calculating duty, the volume of vaping product in any pre-filled container is determined by:
the actual volume of product with which the container is filled
the stated volume on any retail packaging
any stated volume on an invoice issued
any stated volume on a delivery note
any stated volume on a document similar to an invoice or delivery note
Where more than one volume is stated on any of the above and it is different, then the volume of vaping product is taken to be the largest one ascertained or stated. Your approach to this must be a reasonable one and you should not apply this test in cases of obvious error (such as an invoice stating 10 litres for a single bottle of 10 millilitres).
The actual volume must be measured to the nearest:
0.1ml for declared volumes of less than 1 litre
1.0ml for declared volumes of more than 1 litre
Volumetric measurements of the liquid must be taken at a temperature between 18C and 22C.