Running out of shielding gas mid-weld or cutting gas mid-cut wastes time, ruins work, and costs money. Knowing how long a cylinder will last at a given flow rate is basic job planning. A standard K-size argon cylinder at 25 CFH lasts about 11 hours of arc time. A T-size cylinder at the same flow rate lasts about 16 hours. The difference can determine whether you finish a job on one cylinder or need to swap mid-shift.
Cylinder duration depends on three variables: the volume of gas in the cylinder (determined by cylinder size and fill pressure), the flow rate at the regulator, and the duty cycle of the operation. This guide covers standard cylinder sizes, volume calculations, common flow rates by process, and strategies for multi-cylinder job planning.
Standard Cylinder Sizes and Gas Volumes
Compressed gas cylinders are identified by letter designations that indicate their physical size and volume capacity. The most common sizes for welding and cutting gases are R, S, K, and T. An R-size cylinder holds about 20 cubic feet of gas. An S-size holds roughly 40 cubic feet. A K-size (the most common full-size welding cylinder) holds about 270 to 330 cubic feet depending on the gas. A T-size holds approximately 330 to 400 cubic feet.
For argon and argon mixes at standard fill pressure of 2,200 to 2,400 PSI: a size 80 (small) holds about 80 CF, a size 150 holds 150 CF, a K-size holds about 282 CF, and a T-size holds about 400 CF. For CO₂ which is stored as a liquid: a 50-lb cylinder holds about 460 CF, and a 75-lb cylinder holds about 690 CF of gas.
Oxygen and acetylene have different fill methods. Oxygen is compressed gas at 2,200 PSI: a K-size holds about 244 CF. Acetylene is dissolved in acetone at only 250 PSI: a size B holds 40 CF, a number 4 holds 175 CF, and a number 4.5 holds about 290 CF. Never draw acetylene faster than 1/7 of the cylinder capacity per hour to avoid pulling liquid acetone.
Argon K-size: 282 CF | Argon T-size: 400 CF
CO₂ 50 lb: 460 CF | CO₂ 75 lb: 690 CF
Oxygen K-size: 244 CF | Oxygen T-size: 335 CF
Acetylene B: 40 CF | Acetylene #4: 175 CF
Volumes vary by manufacturer and fill pressure.
Compressed Gas Cylinder Duration Calculator
Calculate how long a compressed gas cylinder will last at a given flow rate. Covers standard sizes (R, K, T, S), common gases, and multi-cylinder job planning.
Calculating Cylinder Duration at a Given Flow Rate
Duration (hours) = Cylinder volume (CF) ÷ Flow rate (CFH). A K-size argon cylinder with 282 CF at 25 CFH: 282 ÷ 25 = 11.3 hours of continuous arc time. At 35 CFH for spray transfer MIG: 282 ÷ 35 = 8.1 hours.
Actual working duration is longer because of duty cycle. If you are welding 50% of the time (welding half the shift, prepping and positioning the other half), a cylinder that lasts 11 hours of arc time lasts 22 hours of clock time. Duty cycle makes a big difference in cylinder consumption planning.
For mixed gases (like 75% argon / 25% CO₂), use the total cylinder volume at the stated fill pressure. The mix ratio does not change the volume calculation — it is still a compressed gas at the labeled pressure. What changes is the flow rate setting for optimal weld quality.
Track actual consumption per job type to build your own data. Theoretical calculations assume the regulator is perfectly accurate and there are no leaks. In practice, leaks at connections, flow rates set higher than needed, and pre-flow and post-flow settings all increase consumption beyond the theoretical minimum.
Arc-time hours = Cylinder volume (CF) ÷ Flow rate (CFH)
Clock-time hours = Arc-time hours ÷ Duty cycle (%)
Example: 282 CF argon at 30 CFH, 40% duty cycle:
Arc time = 282 ÷ 30 = 9.4 hours
Clock time = 9.4 ÷ 0.40 = 23.5 hours
Typical Flow Rates by Welding Process
MIG welding (GMAW) short circuit transfer: 25 to 30 CFH for most applications. Spray transfer on thicker material: 35 to 45 CFH. Pulse MIG: 30 to 40 CFH. Higher flow rates do not improve weld quality — they waste gas and can actually cause turbulence that pulls in atmospheric contamination.
TIG welding (GTAW): 15 to 25 CFH for most work. Cup size matters: a number 5 cup needs less flow than a number 8. Gas lens setups allow lower flow rates with better coverage. Walking-the-cup on pipe: 20 to 30 CFH depending on cup size and joint geometry.
Oxy-fuel cutting: oxygen consumption depends on tip size and material thickness. Cutting 1/2-inch steel with a size 1 tip uses about 30 to 40 CFH of oxygen plus 5 to 8 CFH of acetylene for preheat. Cutting 1-inch steel with a size 3 tip uses 60 to 100 CFH of oxygen.
Multi-Cylinder Job Planning and Storage Safety
For large jobs, calculate total gas consumption first, then determine cylinder count. A 40-hour structural welding job at 30 CFH and 50% duty cycle uses 600 CF of shielding gas. That is about 2.1 K-size argon cylinders. Order three to have a spare.
Manifold systems connect multiple cylinders to a single distribution line. A two-bank manifold with automatic switchover provides uninterrupted gas supply. When one bank empties, the system switches to the other while the empty bank is replaced. This eliminates the 10 to 15 minutes of downtime per cylinder change.
Storage safety: keep cylinders upright and chained or capped. Separate oxygen from fuel gases by 20 feet or a 5-foot-tall fire-resistant barrier. Keep cylinders away from heat sources and direct sunlight. Never store more cylinders on site than you will use within a reasonable timeframe — excess inventory is an unnecessary hazard.
Full and empty cylinders should be stored separately and clearly marked. Returning an empty cylinder mixed in with full ones causes confusion and delays when a welder grabs what they think is a full bottle.
1. Store upright, secured with chain or strap
2. Valve caps on when not in use
3. Oxygen 20 ft from fuel gases (or 5 ft barrier)
4. Away from heat, sparks, and electrical circuits
5. Ventilated area, not in confined spaces
6. Separate full from empty, clearly labeled