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.

Shielding Gas Flow Rate Calculator

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.

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 cup sticking past the nozzle exposes the shield and needs more flow.
A gas lens lets TIG run lower flow with a longer, calmer column, useful for reaching into tight joints.
The cost figures count only arc-on time. Real cylinder usage is higher because of purge cycles, leaks, and pre/post-flow.