Checking a cylinder's net weight
The three weights
Tare weight is the empty cylinder including its valve. It is stamped into the metal, usually on the collar or neck ring alongside the test date and specification, because it is a permanent property of that particular cylinder.
Net weight is the refrigerant. This is what you are buying and what the product label states.
Gross weight is the two added together, which is what a scale reads.
The arithmetic is deliberately simple, which is what makes the check practical on a delivery bay rather than in a laboratory.
Doing the check
Weigh the cylinder on a scale accurate enough for the quantity. Read the tare stamped on the collar. Subtract. Compare against the net weight on the label.
A small discrepancy is normal, because filling tolerances exist and a scale has its own error. A meaningful shortfall is not, and it is worth raising before the cylinder is connected rather than afterwards.
The same check at the end of a job tells you how much you actually used, which is the number worth recording if anyone at your site tracks refrigerant for emissions reporting.
Why short filling happens
It is the least detectable fraud in the chain. The cylinder looks right, the label looks right, the gas is real, and there is simply less of it than stated. Nobody notices unless they weigh it, and almost nobody weighs it.
It also compounds quietly. A technician charging by weight will use what the system needs and find the cylinder empties sooner than expected, which reads as normal consumption rather than as a shortfall.
What else the collar tells you
While the cylinder is in front of you, the stamping also carries the specification it was built to, the test pressure, the water capacity and the date of the last hydrostatic test.
That date matters. A refillable cylinder must be periodically retested, and one past due should not be in service. If a supplier is circulating cylinders whose test dates have lapsed, the weight is probably not the only thing worth checking.
See how to read a cylinder label for the full set of markings.
Where this fits in checking authenticity
Weight is one of four checks, and it is the one that needs equipment. The other three are free: a manufacturer's brand on the cylinder, a batch number that matches the paperwork, and an intact seal with no evidence of repainting.
Together they catch the lazy end of counterfeiting, which is most of it. See the buyer's checklist.
Quick answers
How do I check how much refrigerant is in a cylinder?
Weigh it, read the tare weight stamped on the collar, and subtract. The result is the net weight of refrigerant, which should match the product label.
Where is the tare weight marked?
Stamped into the metal, usually on the collar or neck ring, alongside the specification, test pressure, water capacity and last test date.
What is a normal filling tolerance?
A small discrepancy is expected from filling tolerance and scale error. A meaningful shortfall is worth raising with the supplier before the cylinder is used.
Can I reuse a cylinder past its test date?
A refillable cylinder past its periodic hydrostatic test date should not be refilled or kept in service. The date is stamped on the collar.
- Gas Cylinders Rules, 2016 · cylinder marking, tare weight and periodic testing · peso.gov.in.
- AHRI Standard 700 · refrigerant specifications · ahrinet.org.
- US EPA · guidance on counterfeit and contaminated refrigerant · epa.gov.
This guide is general information compiled from the cited sources — not legal, safety or engineering advice. Read our full disclaimer.
Related: Reading a cylinder label · Genuine vs counterfeit · Cylinder sizes we stock · COA and traceability