Tank Ullage and Innage Calculator
Convert a manual ullage (outage) measurement taken from the tank reference point into innage (liquid level) and volume, and find how much can still be received before the safe fill level.
- Innage = reference height − ullage = 15.2 − 3.85 = 11.35 m
- Volume = π/4 × D² × innage = 1,283.7 m³
- Room = A × (safe fill − innage)
Ullage Formulas
Volume = A × innage
Room = A × (safe fill level − innage)
The reference height is the distance from the datum plate (zero) to the gauging reference point at the hatch. Ullage (outage) is the distance from the reference point down to the liquid. A is the tank cross section; real tanks use their certified strapping table instead of the simple area.
Worked example
With a 15.2 m reference height and a 3.85 m ullage, the innage is 11.35 m; a 12 m tank then holds about 1,284 m³ and has 243 m³ of room to a 13.5 m safe fill level.
Frequently Asked Questions
What is the difference between ullage and innage?
Innage is the liquid depth from the datum plate; ullage is the empty space from the reference point down to the liquid.
Why is reference height checked?
It can change with tank settlement, roof deflection or a moved hatch, which shifts every ullage reading.
What is the safe fill level?
The highest level the tank may be filled to, set below overfill and high high alarm levels with time to stop a receipt.
Learn more on the blog
Basics of level measurement
A practical, field focused guide on instrumentationblog.in that explains the theory behind this calculator and how engineers apply it on real plants.
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