“50L-class”, or “B50” in some regions).
For ISO 9809-1, 47.0 L, 150 bar argon cylinders, the officially recognized and universally published gas content is:
≈ 8.0 m3 of argon
= 8,000 liters of argon gas at 15 °C and 1 atm
This is the exact figure you will see on almost every gas supplier’s data sheet, delivery note, or cylinder label for this cylinder:
Specification
Value
47.0 L
Filling pressure
150 bar
Standard
ISO 9809-1
Argon content (full)
8.0 m3 = 8,000 liters
So your cylinder contains