To determine your gas cylinder LPG Worth (LW), first you will need an accurate scale, I will recommend a digital scale for this. By now, you should already know how to set and operate one. If you don't, no worries.
Next, make sure your gas cylinder bottle is empty of LPG gas and other accessories such as regulator, hose pipe, burner and valve are disconnected. Place the gas cylinder bottle on the digital scale. Note, this may give high value figure on the dashboard, little more than expected or in rare cases, less than expected (mostly with substandard gas cylinders). The figure shown is known as the Tare (empty) Weight or total weight. And this value will determine that LPG Worth.
On The Digital Scale:
* A 3kg cylinder bottle that gives 4.(other decimals) can only contain 3 kg and not more. However, 3kg that gives 5.(other decimals) can only contain 4kg LPG Worth and not more.
* A 5kg cylinder bottle that gives 6.(other decimals) can only contain 5kg and not more. However, 5kg that gives 7.(other decimals) can only contain 4kg LPG Worth and nothing more.
* A 6kg cylinder bottle that gives 7.(other decimals) can only contain 6 kg and not more. However, 6kg that gives 8.(other decimals) can only contain 7kg LPG Worth and nothing more.
* A 12.5kg cylinder bottle that gives 14.(other decimals) can only contain 12.5 kg and not more. However, 12.5kg that gives 15/16.(other decimals) can only contain 13/14kg LPG Worth and nothing more.
Tare Weight is the empty weight of the gas cylinder. Along with the gas bottle dimensions, they can vary greatly by manufacturer and date of manufacture. Older bottles tend to be heavier than more recent versions. Also, the material used in manufacturing them can greatly influence the weight and size on the scale.
The above figures for refilling cylinder bottle WILL help prevent overfilling. Overfilling gas bottles can be dangerous, compared to a time bomb. So, to be on a more safer side, you are advice not to refill using the general name (kg) known for cylinder bottles.