Shielding Gas Flow Calculator
Estimate how much shielding gas a job uses and how long a cylinder lasts from the flow rate and arc-on time.
How it works
Gas used (cf) = flow (CFH) × arc-on time ÷ 60 · Cylinder runtime (hr) = cylinder capacity ÷ flow rate
Shielding gas is billed by volume, and a flowmeter set in cubic feet per hour makes the arithmetic simple: gas used equals the flow rate times the fraction of an hour the arc is actually on. Only arc-on time counts, so a job that takes all day but welds for one hour uses one hour’s worth of gas — plus a little for pre- and post-flow. Higher flow does not mean better coverage; too much gas creates turbulence that pulls air into the weld, so set the lowest flow that keeps porosity away (often 20–25 CFH indoors).
Worked example
Welding at 20 CFH for 60 minutes of arc time uses 20 × 60 ÷ 60 = 20 cf of gas (about 566 litres). A full 250 cf cylinder at that flow lasts 250 ÷ 20 = 12.5 hours of actual welding.
Frequently asked questions
What flow rate should I use for MIG?
Indoors, 20–25 CFH suits most MIG work. Push it higher only for large nozzles or drafty conditions — excess flow becomes turbulent and can suck air into the puddle, causing porosity.
Does the whole job time count?
No — only arc-on time consumes gas (plus small pre-flow and post-flow amounts). If you weld for one hour spread across a full shift, you still only use about one hour of gas.
How big are common cylinders?
Hobby and portable bottles run about 40–125 cf, while shop cylinders are commonly 250 cf and up. Divide the cylinder’s cubic feet by your flow rate to see the arc hours it holds.
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This calculator is for educational purposes. Double-check important results before acting on them.