Abstract: Containers such as liquefied gas cylinders are weighed in situ using a balance comprising a pneumatic actuator connected between a support temporarily installed above a container to be weighed and the container itself. Gas pressure is applied to the actuator to lift the container off the surface on which it is standing, and the pressure required to hold it off that surface is measured to indicate the weight of the container. A limiting valve is associated with the actuator so as to limit pressure therein to that required to lift the container.