Tank Ullage Calculator

Work out tank ullage instantly with clear inputs, formula shown and shareable results.

About Tank Ullage Calculator

Ullage is the empty space above the product. The figure that matters operationally is safe ullage — the space up to the safe fill limit, not to the top of the tank. Dividing safe ullage by the incoming rate gives the time available before the receipt must be stopped or diverted.

Formula

Ullage

Safe ullage = capacity x safe fill % - current volume; time available = safe ullage / incoming rate

Worked example

With the default values below, Tank Ullage Calculator returns Safe Ullage Remaining of 3,100.00. Change any input above and every figure here is recalculated in your browser.

Inputs used

Tank Total Capacityminimum 0.01 m3: 10,000 m3
Current Product Volumeminimum 0 m3: 6,400 m3
Safe Fill Limitaccepts 1–100 %: 95 %
Incoming Flow Rateminimum 0 m3/hour: 400 m3/hour

Results

Safe Ullage Remaining: 3,100.00
Total Empty Volume: 3,600.00
Hours To Reach Safe Fill Limit: 7.750
Current Fill Level: 64.00%

Step by step

1Values used
2Ullage
3Safe Ullage Remaining= 3,100.00
4Total Empty Volume= 3,600.00
5Hours To Reach Safe Fill Limit= 7.750
6Current Fill Level= 64.00

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Tank filling must be controlled by independent high-level alarm and automatic overfill protection, not by ullage arithmetic. Overfill of flammable liquids can cause vapour cloud explosions.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Tank filling must be controlled by independent high-level alarm and automatic overfill protection, not by ullage arithmetic. Overfill of flammable liquids can cause vapour cloud explosions.

Frequently Asked Questions

Why is a safe fill limit needed?

It provides the time and volume margin for high-level alarms, operator response and valve closure. Buncefield-type overfill incidents happen when that margin is consumed.

Should ullage be measured or calculated?

Measured, by independent level instrumentation, and cross-checked against calculated ullage from flow totalisers. Discrepancy between the two is an early indication of a leak or a metering fault.