← Back to Bead BoardHow many bottles of shielding gas do I need?
Pick your process, flow rate, and cylinder size. Get the total gas consumption, number of bottles, cost per weld-hour, and how many days each cylinder lasts. Stop guessing and over-ordering.
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How shielding gas consumption actually works
Gas only flows while the arc is on (plus a few seconds of pre-flow and post-flow). A welder set to 25 CFH does not burn 25 cubic feet every hour they are in the shop — it burns 25 cubic feet for every hour the trigger is pulled. In a typical small shop, arc-on time is 3–5 hours per 8-hour shift. The rest is setup, fit-up, grinding, and staring at prints.
That is why you enter arc-on hours, not total shop hours. If you do not know your arc-on time, start at 4 hours per day for production MIG, 3 for mixed fab, or 2 for TIG-dominant work. Track it for a week and adjust.
Cylinder sizes and what they hold
Sizes are industry standard for compressed gas cylinders (argon, CO₂, and blends). Actual fill capacity varies slightly by supplier. Liquid cylinder systems used in high-volume production are not covered here.
How to reduce gas waste without cutting quality
- Fix leaks. Spray soapy water on every fitting from the regulator to the torch. A slow leak you cannot hear can drain 20% of a cylinder overnight if you leave the valve cracked.
- Set flow correctly. Higher flow is not better. Above 35–40 CFH the gas becomes turbulent and pulls ambient air into the weld zone. If you see porosity, try dropping flow 5 CFH before raising it.
- Use a gas lens. A gas lens (screen diffuser in the TIG cup) produces laminar flow, which extends gas coverage with less volume. You can often drop 5–10 CFH with a gas lens versus a standard collet body.
- Shorten post-flow. Default post-flow on many machines is 5–10 seconds. For short beads that is overkill. 2–3 seconds is usually enough for MIG. TIG needs more (the tungsten oxidizes without gas) but not 15 seconds.
- Buy bigger cylinders. Per-cubic-foot cost drops as cylinder size increases. A 330 cf tank costs less than two 125 cf tanks to fill, and you save the swap time.
Questions welders keep asking about shielding gas
How long does a 75/25 cylinder last for MIG welding?
At 25 CFH flow and 4 hours of arc-on time per day, an 80 cf cylinder lasts about 0.8 days — you will swap bottles almost every day. A 125 cf tank lasts about 1.25 days. A 330 cf tank gives you about 3.3 days. Most small shops running production MIG lease a 251 cf or 330 cf tank to avoid constant swaps.
What flow rate should I use for MIG welding?
Start at 20–25 CFH for most MIG work on mild steel with 75/25 Ar/CO₂. Thin material (1/16"–1/8") can drop to 15–20 CFH. Thick material (1/4"+) or spray transfer may need 30–35 CFH. Outdoor work with wind needs higher flow or a wind screen. If you see porosity, your flow may be too low or too high (turbulence pulls air in).
How much argon does TIG welding use?
TIG typically runs 15–20 CFH on steel and stainless (cup size #5–#8). Aluminum often uses 18–25 CFH. Because TIG arc-on time is lower than MIG (more setup, tacking, and cleaning between passes), a cylinder lasts longer than the math suggests if you factor in real-world duty cycle.
What size welding gas cylinder should I buy?
Hobby welders and mobile guys usually run 40 cf or 80 cf tanks because they fit in a truck. Shop welders running production MIG should be on 125 cf minimum, ideally 251 cf or 330 cf. Bigger tanks have a lower per-cubic-foot cost because you amortize the delivery fee over more gas. If you own the tank, larger sizes are almost always cheaper per fill.
How do I calculate gas cost per weld-hour?
Multiply your flow rate (CFH) by your gas cost per cubic foot. At 25 CFH and $0.35/cf (typical for 75/25 mix), that is $8.75 per arc-on hour. This is the number to plug into your job quotes. Total job gas cost = cost per weld-hour × estimated arc-on hours.
Does flux-core use shielding gas?
Gas-shielded flux-core (E71T-1, dual shield) does — typically 100% CO₂ or 75/25 at 35–45 CFH. Self-shielded flux-core (E71T-11, NR-211) does not use external gas at all. If you are running self-shielded wire, your gas cost is zero. This calculator covers the gas-shielded variant.
Why is my gas running out faster than expected?
Common causes: regulator set too high (turbulence pulls in air, so you crank it higher in a loop), gas leaks at fittings (spray soapy water on every connection), long torch lead with loose liner dragging gas, drafts in the shop, or leaving the post-flow running longer than needed. Fix leaks first — many shops lose 20% of their gas to bad fittings.
Other tools in the Tack Box
Cylinder sizes from WeldGuru and WeldItU cylinder charts. Flow rate defaults from Arc-Zone and Miller welding parameter guides. Gas pricing from WeldingWeb forum threads, 2024–2026. Other Tack Box tools.