If you own an LPG gas plant, you may have received LPG from a bobtail truck and wondered how the quantity on the truck flow meter relates to the amount of LPG you actually received into your storage tank.
This is especially important when buying LPG in kilograms while the bobtail truck flow meter displays the quantity in litres.
For example, a customer may order 500kg of LPG, but the meter on the delivery truck may not show 500. Instead, the meter may show a figure in litres.
So, how do you convert the litre reading to kilograms? The calculation is straightforward.
How to Convert LPG Litres to Kilograms
For the practical conversion used in this calculation, divide the quantity shown on the bobtail truck flow meter by 1.75.
Formula
LPG quantity in kg = Flow meter reading in litres ÷ 1.75
For example, if the bobtail truck's meter shows:
875 litres
The calculation will be:
875 ÷ 1.75 = 500kg
Therefore, a flow-meter reading of 875 litres corresponds to 500kg using the 1.75 conversion factor.
Another Example
Suppose a gas plant orders 1,000kg of LPG. To determine the approximate litre reading corresponding to that quantity using the same conversion factor, you can work backwards:
1,000kg × 1.75 = 1,750 litres
So, approximately 1,750 litres on the flow meter corresponds to 1,000kg using this calculation. The same method can be used for other quantities.
| LPG quantity | Flow-meter reading |
|---|---|
| 100kg | 175 litres |
| 200kg | 350 litres |
| 300kg | 525 litres |
| 400kg | 700 litres |
| 500kg | 875 litres |
| 1,000kg | 1,750 litres |
| 2,000kg | 3,500 litres |
| 5,000kg | 8,750 litres |
How Does This Relate to the LPG Storage Tank?
This is where things can become confusing for a new gas plant operator. The bobtail flow meter and the storage tank gauge are measuring different things.
The flow meter on the bobtail records the quantity passing through the delivery system, while the storage tank gauge indicates the level or contents of the tank.
Therefore, you should not expect the storage tank gauge to display the same number as the bobtail meter.
For example, if a bobtail delivers 875 litres, that corresponds to approximately 500kg using the 1.75 conversion factor.
But the storage tank gauge will show the change in the tank's level, normally as a percentage or according to the tank level indication system.
The increase shown on the tank will depend on how much LPG was already inside the tank before delivery and the tank's total capacity.
Why LPG Plant Owners Should Understand the Calculation
The truth is, this conversion is useful when checking LPG deliveries. If you ordered a particular quantity in kilograms but the delivery meter displays litres, you can use the conversion to understand the approximate equivalent quantity.
For example:
> Customer order: 500kg
> Bobtail meter: 875 litres
> Calculation: 875 ÷ 1.75
> Equivalent: 500kg
This gives the plant operator a simple way to understand the relationship between the order and the meter reading.
Don't Confuse Litres With Kilograms
One of the common mistakes is assuming that litres and kilograms are the same measurement. They are not.
Litres measure volume. Kilograms measure mass.
The bobtail flow meter may display volume, while LPG is commonly bought and sold commercially by weight. That is why a conversion factor is needed.
This simple calculation can help LPG plant owners understand the relationship between the quantity ordered in kilograms and the litre reading displayed on a bobtail delivery meter.