Welding: Shielding Gas Hours Left In The Cylinder

Excel Formulas › Welding & Fabrication

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Running out of shielding gas mid-weld ruins a bead and wastes a setup. A gas cylinder's remaining contents scale with gauge pressure, so a half-pressure cylinder holds about half its gas. This recipe estimates the cubic feet left and divides by your flow rate to give hours of arc time remaining.

Quick formula: Cubic feet times gauge pressure over full pressure, divided by flow in cubic feet per hour:

=ROUND(B2*C2/D2/E2,1)

An 80 cu ft cylinder at 1,200 of 2,200 psi flowing 20 cfh has about 2.2 hours left.

Functions used (tap for the full reference guide):

ROUND

The example

Three cylinders at different pressures and flow rates. Higher flow rates empty the same cylinder much faster.

	A	B	C	D	E	F	G
1	Case	Cu ft	Gauge psi	Full psi	Flow cfh	Hours left	Cu ft left
2	Shop bottle	80	1,200	2,200	20	2.2	43.6
3	Large bottle	125	2,000	2,200	25	4.5	113.6
4	Nearly empty	80	400	2,200	35	0.4	14.5

The formula

Remaining gas scales with pressure; hours are remaining gas over flow:

=ROUND(B2*C2/D2/E2,1) // hours left; cubic feet left = CuFt*Psi/FullPsi

How it works

Here is the logic, one piece at a time:

C2/D2 is the fraction of full pressure still in the cylinder.
B2*C2/D2 converts that fraction to cubic feet of gas remaining.
Dividing by the flow rate in E2 gives hours of welding at that flow.
ROUND(...,1) trims the answer to a tenth of an hour.

This is an estimate: temperature and gas mix shift the gauge reading, and CO2 cylinders hold liquid so pressure stays flat until nearly empty.

Try it: interactive demo

Interactive

Enter the cylinder size, gauge pressure, full pressure and flow rate.

Cylinder size (cu ft)

Gauge pressure (psi)

Full pressure (psi)

Flow rate (cfh)

Variations

Convert to minutes

Multiply by 60 to read the answer in minutes of arc time.

=ROUND(B2*C2/D2/E2*60,0)

Reserve a swap-out margin

Treat the last 200 psi as empty and swap the bottle before then.

=ROUND(B2*MAX(0,C2-200)/D2/E2,1)

Pitfalls & errors

Do not use this for CO2 cylinders; they hold liquid and the gauge stays near constant until almost empty.

Flow rates on regulators are set for the bead, not the whole shift. Use your real average.

Write the date and starting psi on the cylinder tag so the next shift can compare.

Practice workbook

📊

Download the free Welding: Shielding Gas Hours Left In The Cylinder practice workbook

Edit the yellow size, pressure and flow cells; hours and cubic feet left recalculate.

Frequently asked questions

Where do I find the full pressure and cubic feet?

They are stamped on the cylinder or listed by the supplier; common full pressures are 2,000–2,265 psi.

Does this work for argon/CO2 mixes?

Yes, they behave as compressed gases, so pressure is a good gauge.

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Function references: ROUND