What flow rate should I use for MIG welding?

A common starting point is roughly 1.8 CFH per millimetre of nozzle inner diameter, which puts a typical 16 mm nozzle around 30 CFH or 14 L/min indoors. Increase it in draughty conditions and decrease it if the shield is clean and quiet.

Why can too much gas flow cause porosity?

Excessive flow turns the laminar gas shield turbulent. The turbulence pulls surrounding air into the weld zone, so nitrogen and oxygen reach the molten puddle and create porosity, the very defect more gas was meant to prevent. The aim is a smooth, quiet shield, not maximum flow.

How do I weld outdoors with shielding gas?

Wind quickly strips a gas shield away, and simply raising flow makes it worse by adding turbulence. Use a wind screen, weld in an enclosure, or switch to a self-shielded flux-cored wire that carries its own protection. Above about 8 km/h of wind a gas-shielded process struggles.

How is gas consumption per metre calculated?

Flow in cubic feet per hour is converted to cubic feet per minute, then multiplied by the arc minutes needed to weld one metre, which comes from the travel speed. Faster travel uses less gas per metre because the arc spends less time over each section of joint.

Does TIG use less gas than MIG?

Generally yes, because TIG cups are smaller and the process is slower and more localised. This tool uses a lower flow factor for TIG, but the right value still depends on cup size, gas lens use, and how exposed the joint is.

What is the Shielding Gas Flow Rate Calculator?

Recommend shielding gas flow rate in CFH and L/min from nozzle diameter, process, and indoor or outdoor conditions for GMAW and GTAW. Also estimates gas consumption per arc-hour and per metre of weld, plus cost at your gas price. It runs free in your browser on Gera Tools, with nothing uploaded.

Shielding Gas Flow Rate Calculator

Name: Shielding Gas Flow Rate Calculator
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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The shielding gas keeps oxygen and nitrogen away from the molten weld pool. Set the flow too low and air reaches the puddle, causing porosity; set it too high and the stream turns turbulent and aspirates air anyway. This calculator gives a sensible starting flow from the nozzle size and conditions, then estimates how much gas a job will burn and what it costs.

How it works

Flow scales mainly with the nozzle (or TIG cup) inner diameter, with a process factor and a condition multiplier:

flow_CFH = nozzle_ID_mm x k x condition
  k:          MIG ~ 1.8 CFH/mm     TIG ~ 1.3 CFH/mm
  condition:  indoor 1.0   draught 1.3   outdoor 1.6

Consumption follows directly. Cubic feet per hour equals the flow during arc time, and per metre of weld it uses the travel speed:

arc_minutes_per_metre = 1000 / travel_speed_mm_per_min
gas_per_metre_ft3     = (flow_CFH / 60) x arc_minutes_per_metre

One CFH equals about 0.472 litres per minute.

Worked example

A MIG welder with a 16 mm nozzle, welding indoors, travelling at 400 mm/min:

Flow = 16 × 1.8 × 1.0 = 28.8 CFH (about 13.6 L/min)
Arc time per metre = 1000 / 400 = 2.5 minutes
Gas per metre = (28.8 / 60) × 2.5 = 1.20 ft³/metre (about 34 litres/metre)

At 500 mm/min the travel is faster, so gas per metre falls to about 0.96 ft³ — faster welding costs less gas per joint, even though the flow rate is the same.

Common gas mixes for MIG and TIG

Process	Gas mix	Typical use
MIG (GMAW)	75% Ar / 25% CO₂ (C25)	Mild steel, general fabrication
MIG (GMAW)	90% Ar / 10% CO₂	Thin steel, spatter reduction
MIG (GMAW)	100% CO₂	Budget mild steel welding
MIG (GMAW)	98% Ar / 2% O₂	Stainless steel
TIG (GTAW)	100% Argon	Most metals including alu and stainless
TIG (GTAW)	Ar / 5–25% He	Higher heat input; thicker aluminium

The gas mix changes the arc characteristics, bead appearance, and penetration profile — but it does not change the flow-rate calculation. Use this calculator with any mix; only the nozzle size and conditions determine the appropriate flow.

Tips and notes

Treat the result as a starting point and trim it down to the lowest flow that still gives a clean, sound bead — that saves gas and reduces turbulence.
A longer contact-tip-to-work distance or a longer TIG cup sticking past the nozzle exposes the shield to air and needs more flow.
A gas lens attachment for TIG replaces the standard collet body and collet, allowing a longer, calmer gas column at lower flow — especially useful for reaching into corners or welding exotic alloys that need maximum protection.
The cost figures count only arc-on time. Real cylinder usage is higher because of purge cycles, cylinder pressure losses, post-flow (essential for TIG to protect the cooling tungsten), and any pre-flow.
Wind is the enemy of gas shielding. Even a 5 mph breeze can strip away the shield. If you must weld outdoors, use a wind screen; above about 8 mph consider a self-shielded flux-cored wire instead.