GLP mass to volume conversion problem (Rotary Meter)

this is my first post here on this forum.
I would like to share a question that is bothering me:


I have a gas powered system.
I would like to measure the total gas consumption in `kg`.
The problem is that the meter I use gives me the value in `m³`.
I use the g10 DN40 threaded delta meter from the link below.
It is a rotary principle meter.


<https://www.itron.com/-/media/feature/products/documents/brochure/delta-en-web.pdf>


Currently I use the factor of `2.5kg/m³` for the conversion.


The system is periodically supplied with lpg gas and the supplier gives me an invoice with the total value of gas supplied in `kg`.


When adding up the total supply carried out in the cylinders within a period of a few months and comparing with the consumption measured by the meter, in the same period, I always obtain lower consumption values. Could it be that the company is supplying me with less gas than it says.


Note: The gas meter is not right after the cylinders.
he is after a few meters of pipes and after a pressure reducer.


Do I need to do a temperature and pressure compensation to get another conversion factor from `kg` to `m³`?


