How much gas is left in my CO2 cylinder

Nowadays using CO2 cylinders at home is becoming more and more popular . People use CO2 for making fizzy drinks, to fertilise aquariums and they use CO2 even for amateur welding. Whatever is the reason of using the CO2 cylinder at home, there will be a question at some point: how much CO2 is left in my cylinder… You can see very often CO2 regulators with the pressure gauges. The problem with CO2 is that the gas in the cylinder is compressed so much that is becomes liquid. The gauge always shows the pressure around 5.9MPa (860 psi, 59.3bar). It means the pressure inside is roughly 60x greater then the air. The normal air pressure is 1atm which is around 1bar which is also roughly 1000hPa 🙂 The expansion rate is 535:1.

As mentioned, CO2 inside is in the liquid state, so all the gauges show a constant pressure, regardless the cylinder is full or almost empty. When the gauge pressure drops, in happens quite quickly and it means the cylinder is practically empty.

The only one way to sort out how much gas is left in the cylinder is to weight the cylinder. If you forgot to weight the cylinder when it is full, you may struggle to find out how much CO2 gas is left. But there is something very helpful. All legally made cylinders have got some signs stamped on the cylinder – see some sample pictures below.


The sign says TARE 11.4KG 6.35KG CO2 – and it is right, when I bought my 6.35kg CO2 cylinder the weight was 17.6 (should be 17.75). It means 150g of CO2 was missing 🙂

The full sign on my cylinder says:


3.45MM 10.6KG 8 7L PH300BAR TARE 11.4KG 6.35KG CO2

110036 EN ISO 9809-1 D 2017/01

It means my huge CO2 cylinder is empty when its weight is 11.4kg (10.6kg without the valve)


My other cylinder – CO2 extinguisher 2kg (above) shows the following signs:

CM0LT EN ISO9809-1 OT1.9MM 2KG CO2 3.0LM25 88375

PS174 PT250BAR TS30/60OC 3.86KG TARE 4.34KG CE0036 2020/11

It means my CO2 extinguisher is empty when its weight is 4.34kg (3.86kg without the valve)


And my last Sodastream CO2 bottle (shown above) shows the following signs:

M18 IL LEP 65722195 AA6061 SODA-CLUB

PH250BAR 0.61KG 3.2MM 0.605L TARE 0.75KG 0.453KG 1013 CO2

ISO 7866 G3 UKPI0038 SC 2021/01 2031

It means my empty Sodastream cylinder weight is 750g (610g without the valve). It takes 425g CO2 so I am not sure why it is stamped as 0.453KG

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