Ullage
The empty distance between the surface of a liquid in a tank and a fixed reference point at the tank top; the measurement tankers use to determine cargo volume.
Quick facts
- Complement of
- Sounding
- Measured with
- Ullage tape or automatic tank gauge
In practice
The cargo officer takes ullages, temperatures, and water dips tank by tank at load and discharge, then applies trim and list corrections from the calibration table before converting to standard volume. A gauge error feeds straight into the Bill of Lading figure, so ullaging is done carefully and, for custody transfer, often jointly with an independent surveyor.
Regulatory detail & full definition
Ullage is the vertical distance from the surface of a liquid cargo up to a fixed reference point (the ullage reference gauge point) at the top of a tank — in effect, the empty space above the cargo. It is the complement of the sounding, which measures the depth of liquid from the surface down to the tank bottom or datum. Tankers work primarily in ullage because it is more convenient and safer to gauge from the deck. An ullage is measured with an ullage tape and bob, or read from a fixed automatic tank-gauging system (float, radar, or servo gauge), together with the cargo temperature and the free-water depth. The ullage is then converted to a volume using the tank's calibration (capacity) table and corrected for the ship's trim and list at the moment of measurement. Accurate ullaging underpins the entire cargo-quantity calculation and any ship/shore reconciliation.
Authoritative source: ASTM D1250 — Petroleum Measurement Tables ↗
Related
Source: Petroleum measurement practice (ASTM D1250 / API MPMS)
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