Ullage

Ullage is the unfilled space inside a container, tank, barrel, or other vessel that holds liquid or granular cargo. The term originates from the wine and spirits industry, where it referred to the gap between the liquid level and the top of a barrel. In logistics and freight, ullage describes the empty volume left intentionally or unintentionally in a tank container, ISO tank, drum, or bulk liquid vessel during transport. This space is not wasted; it serves a specific physical purpose.

Why Ullage Exists

Liquids expand when heated. A tank filled to 100% capacity at a factory in Shanghai at 15 degrees Celsius will exceed its volume limit if it reaches 35 degrees Celsius while sitting on a port terminal in the summer sun. The resulting pressure can rupture seals, crack valves, or breach the tank itself. Ullage provides the expansion room needed to accommodate temperature-induced volume changes during transit. The required ullage percentage depends on the liquid’s coefficient of thermal expansion, the expected temperature range during transport, and the regulatory requirements for the specific commodity.

For most non-hazardous liquids, tank containers are filled to 80% to 95% of their total capacity. Hazardous liquids have stricter fill limits dictated by the IMDG Code (for ocean transport) and 49 CFR (for domestic U.S. transport). Flammable liquids, for example, generally must not exceed 95% of the tank’s capacity at the reference temperature of 15 degrees Celsius, with additional margins calculated based on the maximum expected ambient temperature during the journey.

Calculating Ullage

Ullage can be expressed as either a percentage of total tank capacity or as a physical measurement from the top of the tank to the liquid surface. For a 24,000-liter ISO tank filled to 80% capacity, the ullage is 20%, or 4,800 liters of empty space. Measuring ullage physically involves using an ullage rod (a calibrated measuring stick inserted through the tank’s top opening) or electronic sensors that measure the distance from the sensor to the liquid surface. Modern tank containers use automated level sensors that transmit fill data electronically, reducing the need for manual measurement.

In the petroleum industry, ullage measurements are taken at multiple points during transport: at the loading terminal, upon arrival at the discharge terminal, and sometimes at intermediate waypoints. Discrepancies between loading and discharge ullage measurements, beyond what can be attributed to temperature changes, indicate potential leakage or theft.

Ullage in Dry Cargo

While ullage is primarily a liquid cargo term, the concept applies to dry bulk materials as well. Grain, sugar, fertilizer, and other granular commodities shift and settle during transport, creating a gap between the cargo surface and the top of the container or hold. This settling can affect weight distribution, container balance, and the cargo’s susceptibility to moisture damage if condensation forms in the empty space above the product (similar to “container rain” in standard dry containers).

For bulk grain shipments in ocean vessels, ullage measurements verify the quantity loaded against the bill of lading. Independent surveyors measure ullage in each hold before and after loading, converting the measurements to volume and then to weight using the commodity’s known density. This draft survey process is the primary method for verifying bulk cargo quantities in international trade.

Operational Relevance

Most FBA sellers will never deal with ullage directly unless they are importing liquid products in bulk containers. Sellers importing large quantities of sauces, beverages, cleaning solutions, or personal care products in IBC (Intermediate Bulk Container) totes or drums should understand that ullage is not a shortage. A 275-gallon IBC tote filled to 90% capacity holds 247.5 gallons, with the remaining space left intentionally. Receiving warehouse teams who flag a “short” tote without understanding ullage can create unnecessary disputes with suppliers. Prep centers like MeisterPrep that handle liquid product shipments account for ullage during the receiving process, verifying quantities against the supplier’s fill specifications rather than assuming the container should be completely full.