Ullage

This term is used to describe the empty space in large tanks used to transport liquids or grain. Marine transport regulations will prevent a tank from being filled to 100% of its capacity, placing a limit such as 98% on the available capacity. The 2% unused capacity is known as ullage.

In short

Ullage is the empty space between the top of a liquid, or a bulk cargo, and the top of its container. It leaves room for the contents to expand, and in shipping it is also how the quantity in a tank is measured.

Ullage meaning in shipping

On tankers, an ullage is also the measurement itself: the distance from a fixed reference point at the top of the tank down to the surface of the cargo. Crews and cargo surveyors take ullages with a tape or electronic gauges, then use the ship's calibration tables to turn each reading into a volume. The volume is corrected for trim, list and temperature, then converted to weight using the cargo's density. The reverse measurement, from the bottom of the tank up to the liquid surface, is a sounding.

Filling limits exist because liquids expand as they warm. For gas carriers, the IMO's IGC Code sets a filling limit of 98% at the reference temperature, unless the flag administration allows more.

Ullage in drinks and liquids

• Wine and spirits: the air gap between the liquid and the cork or cap, which allows for expansion with temperature.
• Beer and pubs: in the licensed trade, ullage also means beer lost or wasted, such as the residue left in a cask or keg, or beer lost at the tap. Beer left in customers' glasses does not count, because it has been sold. Pubs track ullage to reconcile stock against sales, and some brewery supply agreements set a wastage allowance.

Why ullage matters to buyers

• Bulk liquids are often invoiced on the quantity measured at loading or discharge, so the contract should set the measurement method, temperature correction and who appoints the surveyor.
• Ship and shore figures rarely match exactly. Agree in advance how differences will be settled.
• For drinks, the agreed ullage or wastage allowance changes the true cost per serve.
• In storage tanks, ullage is the capacity still available, which matters when booking storage or planning deliveries.