How much CO₂ is really in a cylinder, and when to move to a tank

Published: 7 September 2026Updated: 15 September 20264 min read

CO₂ LabEngineering team, CO₂ Lab

Cryogenic cylinders in a stainless steel frame on a customer site

A 40-litre cylinder does not hold 40 kg. Here is how much CO₂ each size really carries, how many cylinders your consumption burns through, and the point where a tank starts to cost less.

«How many kilograms are in a 40-litre cylinder?» is one of the most common questions we get. The answer confuses people because a cylinder is measured in litres of water capacity, while the gas inside is sold by the kilogram — and the two numbers are not the same.

Litres of the shell, kilograms of the product

The number stamped on the neck — 10, 20, 40, 50 — is the water capacity of the steel shell, not the mass of CO₂. Carbon dioxide is liquefied under pressure, and the filling ratio is limited by the cylinder's test pressure: roughly 0.6 to 0.75 kg per litre. Overfilling is dangerous, so a filling station will never give you «40 kg in 40 litres».

Cylinder (water capacity)	CO₂ mass	Gas released	Gross weight
10 l	6–7 kg	3.2–3.8 m³	~22 kg
20 l	12–14 kg	6.5–7.6 m³	~40 kg
40 l	24–28 kg	13–15 m³	~85 kg
50 l	30–35 kg	16–19 m³	~105 kg

Filling ratio 0.6–0.75 kg/l; 1 kg of CO₂ gives about 0.54 m³ of gas at 15 °C and 1 bar

Two practical consequences. First, when you compare supplier quotes, compare the price per kilogram of CO₂, not per cylinder. Second, one or two kilograms always stay in the cylinder as an unusable heel and go back to the filler — you paid for gas you never used.

How long a cylinder lasts

Use	10 l cylinder (6–7 kg)	40 l cylinder (24–28 kg)
Welding post, 12 l/min, 50% arc-on	about one shift	4–5 shifts
Beer dispensing, 50 l kegs	40–60 kegs	150–220 kegs
Soda and drinks machine	several weeks	several months

Typical figures; real use depends on flow setting, line length and temperature

A welding post at 12 l/min draws about 1.3 kg of CO₂ an hour of arc. For dispensing, most of the gas goes on pushing beer out of the keg, so a long line and high pressure shorten the figures noticeably.

How many atmospheres are in a full cylinder

Cylinder temperature	Pressure, bar (absolute)
−20 °C	≈ 20
0 °C	≈ 35
+15 °C	≈ 51
+20 °C	≈ 57
+31 °C	≈ 74 — critical point, the liquid disappears

Pressure of liquefied CO₂ depends only on temperature while liquid remains

That is why the gauge says nothing about how much is left: a cylinder at 20 °C shows about 56 bar both when full and with a kilogram of liquid remaining. The pressure only starts to fall when the liquid is gone. The reliable method is to weigh the cylinder and subtract the tare stamped on the neck.

How many cylinders your production actually burns

Take a 40-litre cylinder at 24 kg as the working unit and divide your monthly consumption by it. The result is usually higher than people expect.

Consumption	Cylinders per month	Swaps per week	What it means in practice
100 kg	4	1	Cylinders are comfortable
500 kg	21	5	Still workable, storage starts to hurt
1 t	42	10	Two swaps every working day
3 t	125	29	A dedicated person on cylinders alone
10 t	417	96	Only a stationary tank makes sense

One 40 l cylinder ≈ 24 kg of CO₂

At around one tonne a month the logistics stop being background noise. Someone rolls cylinders, someone signs delivery notes, the line stops while a cylinder is being changed, and the yard permanently holds two sets — full and empty.

Microbulk tank with piping and a vaporizer installed next to a production building — A microbulk vessel is the intermediate step between cylinders and a large stationary tank

The costs that never appear on the invoice

The heel: 1–2 kg per cylinder, which is 4–8% of the contents.
Manual handling. A full 40 l cylinder weighs about 85 kg and must be moved, secured and connected.
Downtime at every swap, multiplied by the number of swaps.
Deposit or rent on the cylinder fleet, plus the space to store two sets of them.
Pressure drop at the end of a cylinder, which shows up as unstable process parameters before anyone notices the cylinder is empty.

What the next step looks like

For nitrogen, oxygen and argon the intermediate format is a cryogenic cylinder: a vacuum-insulated vessel of 180–500 litres that holds liquefied gas and replaces a whole pack of pressure cylinders — see cryogenic cylinders. For CO₂ the usual next step is a stationary tank from 10 m³, which holds about 9.5 tonnes and is refilled by road tanker.

Format	Typical consumption	Inside	Servicing
40 l cylinders	up to 300 kg/month	gas under 50–60 bar	manual swap
Cryogenic cylinder 180–500 l	0.3–1.5 t/month	liquefied gas	swap every 1–3 weeks
Stationary tank 10–30 m³	from 2 t/month	9.5–29 t of liquid	tanker refill on schedule

How to find your own break-even point

Pull the delivery notes for the last three months and add up the kilograms, not the cylinders.
Divide the total invoice by those kilograms — that is your real price per kilogram, heel included.
Add the hours your staff spend on swaps and the cost of the downtime around them.
Compare the result with a tank: bulk CO₂ delivered by tanker is normally two to four times cheaper per kilogram.

In most cases the arithmetic turns at somewhere between one and two tonnes a month. Below that, cylinders win on simplicity; above it, a 10–20 m³ tank pays for itself in a year or two on the price of gas alone.

Frequently asked questions

Why does a 40-litre cylinder hold only 24 kg?

Because litres describe the volume of the shell and kilograms describe the liquefied CO₂ inside it. The filling ratio is limited to roughly 0.6–0.75 kg per litre so that the liquid has room to expand when the cylinder warms up. A cylinder filled to the brim would build dangerous pressure on a hot day.

How long does a 10 l CO₂ cylinder last?

A 10 l cylinder holds 6–7 kg of CO₂. That is about one shift for a welding post at 12 l/min with half the time under arc, or roughly 40–60 kegs of beer at normal dispensing pressure.

Can we fill our own cylinders from a stationary tank?

Technically yes — it needs a filling ramp, a pump and cylinder weighing. Legally it is a separate activity with its own permits, personnel training and cylinder inspection records. For most producers it is simpler to keep bulk supply for the process and buy the few cylinders they still need.

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The question comes up when cylinders have become expensive but a stationary tank still looks like a big commitment. The answer is decided by three numbers, not by preference.

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