Shielding Gas Cylinder Duration Calculator
Work out how long a shielding-gas cylinder will last. Pick the cylinder, enter the flow and how much of the day the arc is on, and get the hours of welding, the shop hours and days it covers, and the gas cost per hour, for a full cylinder, a part-used one, or CO₂ by weight.
How to Use
- Choose Full cylinder, Part-used (by gauge) or CO₂ by weight.
- Pick your cylinder. The US sizes are Airgas argon cylinders by their stated contents; the 200 and 300 bar sizes are European argon cylinders by water capacity. Choose Your cylinder to type the contents yourself.
- Enter the flow from your flowmeter in CFH or L/min, the share of the working day the arc is actually lit, and the hours you work per day.
- For a part-used cylinder, enter the gauge pressure now; leave the full pressure blank to use the service pressure. For CO₂, weigh the cylinder and enter its tare weight.
- Add the price of a fill to see the gas cost per hour of arc. Show Work lists every step and conversion.
Worked Example
A full cylinder. Airgas’s size-80 argon cylinder holds about 85 ft³. MIG welding at 25 CFH gives 85 ÷ 25 = 3.4 hours of arc. With the arc lit 30 % of the working day, that is 3.4 ÷ 0.30 = 11.33 shop hours, or 1.42 eight-hour days. At 60 a fill the gas costs 60 × 25 ÷ 85 = 17.65 per arc hour.
A part-used cylinder. The same cylinder reads 1,000 psi; its service pressure (DOT 3AA2015) is 2,015 psi. It is 1,000 ÷ 2,015 = 49.6 % full, about 42.2 ft³, which lasts 1.69 arc hours at 25 CFH.
The common mistake: reading a CO₂ gauge like an argon gauge. A CO₂ cylinder with only 5 lb of liquid left still reads the vapour pressure of the liquid, 831 psi absolute at 20 °C, so the gauge looks just as full as it did with 50 lb in it. Taking that as a full cylinder predicts 437.1 ft³ and 14.57 hours at 30 CFH; the real figure is 5 × 8.742 = 43.7 ft³, under 1.5 hours. Weigh CO₂ cylinders.
Show Work
Formulas
Where the Cylinder Figures Come From
The US sizes are Airgas’s own product pages for industrial-grade argon, which give the approximate contents of each cylinder in cubic feet (size 80 about 85 ft³, size 125 about 126 ft³, size 300 about 336 ft³) and the DOT specification stamped on it, such as 3AA2015, where the last number is the service pressure in psi. Airgas notes that the actual volume can vary. Its CD 50 carbon dioxide cylinder holds 50 lb of CO₂ in a size-200 cylinder that weighs 106 lb.
European cylinders are sold by water capacity and fill pressure. Argon at 200 bar is not quite an ideal gas, so the litres of gas per litre of cylinder come from the NIST Chemistry WebBook: argon at 15 °C has a density of 357.7 kg/m³ at 200 bar (gauge) and 1.691 kg/m³ at one atmosphere, a ratio of 211.6. At 300 bar the ratio is 302.5, and 50 L × 302.5 = 15,123 L agrees with the 15.14 m³ on BOC’s cylinder identification chart for a PURESHIELD argon E50 at 300 bar. Mixed argon–CO₂ gases are close to argon but not identical, so treat those as approximate.
CO₂ is different because it is stored as a liquid. NIST’s saturation data show the pressure above liquid CO₂ is set by temperature alone (34.9 bar absolute at 0 °C, 57.3 bar at 20 °C, 64.3 bar at 25 °C), so the gauge cannot show the contents; the weight can. OSHA’s rule for gas cylinders (29 CFR 1910.253) requires regulators to come off and valve caps to go on before a cylinder is moved, unless it is secured on a special truck.
About This Tool
This calculator turns a cylinder and a flow rate into hours of welding, shop hours and working days, and adds the gas cost per hour when you enter the price of a fill. It handles a full cylinder, a part-used argon cylinder from its gauge, and CO₂ by weight, with flows in CFH or L/min and volumes in cubic feet or litres. Prices are examples for you to replace. Set the flow from your welding procedure or the wire and gas supplier’s data sheet, and store cylinders where they can’t be knocked over.
Everything runs in your browser; nothing you enter is sent anywhere.
Related tools: Welding Shielding Gas Mixture Chart, Welding Cost Estimator, and Welder Duty Cycle Calculator.
Frequently Asked Questions
How long does an 80 cubic foot argon cylinder last?
Airgas states its size-80 argon cylinder holds about 85 ft³. At 25 CFH that is 85 ÷ 25 = 3.4 hours of arc-on time. If the arc is lit 30 % of the time, the cylinder covers 3.4 ÷ 0.30 = 11.33 hours in the shop, about a day and a half of 8-hour shifts.
How do I convert CFH to litres per minute?
Multiply by 0.4719: one cubic foot is 28.317 litres and an hour is 60 minutes. So 25 CFH is 11.80 L/min, 35 CFH is 16.52 L/min, and 15 L/min is 31.78 CFH.
Can I tell how much argon is left from the gauge?
Yes, roughly. Argon stays a gas, so the amount left goes down almost in step with the gauge pressure: NIST data for argon at 15 °C put the gas at 100 bar at 49.7 % of the gas at 200 bar. An 85 ft³ cylinder filled to 2,015 psi and reading 1,000 psi has about 42.2 ft³ left.
Why does my CO₂ gauge read full until it suddenly runs out?
CO₂ is a liquid in the cylinder, so the gauge shows the vapour pressure of the liquid, which depends on temperature, not on how much is left: NIST gives 57.3 bar (831 psi) absolute at 20 °C and 64.3 bar (933 psi) at 25 °C. The pressure only falls once the liquid is gone. Weigh the cylinder and subtract the tare weight instead.
How much gas is in a 50 litre cylinder at 200 bar?
For argon at 15 °C, NIST densities give 211.6 litres of gas per litre of cylinder at 200 bar, so a 50 L cylinder holds about 10,579 L (10.6 m³). At 300 bar it is 302.5 litres per litre, or 15,123 L, which matches the 15.14 m³ BOC lists for its PURESHIELD argon E50 300-bar cylinder.
How do I use the Shielding Gas Cylinder Duration Calculator?
Just type your numbers. The answer shows up right away — there is no button to press. Change anything and it updates by itself.
Is it free? Does it work without internet?
Yes to both. It is free with no sign-up, and once the page has loaded it keeps working even with no internet.
Where does my data go?
Nowhere — every calculation runs on your own device. Nothing you enter is uploaded, logged, or stored.
Common Use Cases
Ordering gas for a job
A TIG job at 15 CFH with the arc on 20 % of the time: a 336 ft³ (size 300) argon cylinder gives 22.4 arc hours, 112 shop hours, or 14 eight-hour days.
Pricing gas into a quote
A fill of 60 for 85 ft³ used at 25 CFH costs 60 × 25 ÷ 85 = 17.65 per hour of arc, or 5.29 per shop hour at 30 % arc-on.
Metric shops
A 50 L argon cylinder at 200 bar used at 12 L/min lasts 10,579 ÷ 12 = 881.5 minutes, 14.69 hours of arc.
Will it last the weekend?
An 85 ft³ cylinder reading 1,000 of 2,015 psi still holds 42.2 ft³: 1.69 arc hours at 25 CFH.
CO₂ for MIG
A CD 50 CO₂ cylinder weighing 131 lb with a 106 lb tare has 25 lb left, 218.6 ft³ of gas: 7.29 hours at 30 CFH.
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