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What's the difference between litres and litres VDA for boot capacities?

Not every boot size is measured the same way.

The way we measure things, effectively, keeps us all from going bonkers.

Think of money, for a start, and how annoying it is that there are so many currencies. Wouldn't it be easier if there was a single, global dollar? (mind you, that would make it easier to notice how expensive things are in Australia)

Much of Europe realised this some time ago and attempted to bring in a single currency, the Euro, to make life easier. The English, of course, held on to their pound, which is the world's oldest currency that's still in use, and refers, originally, to the equivalent of one pound weight of silver.

Generally, we all manage to agree on most measures, although a few standouts hang on to miles over kilometres, just to be irascible.

Things like wheels, however, are measured in inches, and anyone who tries to convert a 20-inch wheel to centimetres will be deeply scorned by their car enthusiast friends for evermore.

The car world needs to agree on these things to make life easier for customers, who obviously spend a lot of time researching their car-buying decisions and need to be able to make like-for-like comparisons, which is why if some car companies decided to quote fuel economy in miles per gallon rather than litres per 100km, we'd all go mad. Dogs lying down with cats, fire from the skies, proper disaster stuff. At least in the world of cars.

Which is why it's so strange that the boot volume of new vehicles - a singularly important figure for anyone buying a car, and even more so if they have children/prams/bicycles/dogs, etc. - is measured in different ways.

To make it more confusing, each of those different ways seems to use the actual unit of measurement - litres - and yet comes up with different figures.

Some car companies - Mazda, Honda, Toyota, Kia, Hyundai, Citroen, Audi, BMW - measure boot volume using something called VDA, which is short for Verband der Automobilindustrie, which translates as the German Automobile Industry Association.

Intrusion from boot hinges as you shut the lid are another argument in favour of VDA measurement.

Being German, it's both exact and exacting, as you'd expect, and is carried out using blocks of wood measuring 200mm x 50mm x 100mm.

Grab your phone's calculator and do the math if you like, or simply believe us when we say   that this adds up to 1,000,000 cubic millimetres.

A maths teacher might be able to explain to you that 1cm cubed has the same volume as 1 millilitre. So 1,000,000 cubic millimetres works out as one litre.

So, if you can just stop rubbing your forehead and groaning for a minute, you can take it as read that each of these blocks of wood is the equivalent of one litre of boot space, so if you count up all the blocks that fit into a load area (and what a wonderful, giant game of Jenga that must be), you'll get the VDA number of any given car boot in litres.

Fortunately, car companies will just tell you this number, so you don't have to do it yourself.

Mazda Australia, which is a fan of the VDA system, tell us that, "in practice this would be simulated by computer, not with physical blocks," which is a relief.

"The reason for using blocks is to prevent overstating luggage capacity due to irregular shaped luggage compartments," a helpful Mazda spokesperson adds. Intrusion from boot hinges as you shut the lid are another argument in favour of VDA measurement.

If you want to compare a car that doesn't specify whether its boot volume is measured in VDA, call the local dealer and tell them to do the conversion for you.

Now, if everyone agreed that VDA was the one and only way of measuring luggage space, then you'd have some chance of understanding how it's done, but sadly some people prefer a standard called SAE, which stands for Society of Automotive Engineers, one of those US-based organisations that considers itself "International". Their system uses smaller blocks, so you end up with a larger litre figure - or liter figure - which sounds more impressive.

Or, if you check with Jeep or Dodge you'll get the SAE Cargo Volume, measured in cubic metres (a Jeep Cherokee offers 0.7, with rear seats up, good luck making sense of that).

And, to make things worse, other companies, like Holden, Ford, Nissan/Infiniti, Peugeot and Renault - simply quote their boot volume in "litres". We'd like to imagine they work it out by pouring four-litre tubs of ice cream into a car boot until it's full and then counting the empty containers, but this seems unlikely (at least outside of the US).

In short, outside of those companies that helpfully agree on using the VDA method - and surprisingly even the Japanese seem to believe that, in this case, the German way is the best - it can be extremely confusing to compare one car's luggage-carrying space with another's.

One man's litres, it seems, are not always the same as another's, and working it out yourself - unless you're Stephen Hawking - might well do your head in.

So here's our advice. If you want to compare a car that doesn't specify whether its boot volume is measured in VDA, call the local dealer and tell them to do the conversion for you.

Or, if you're more practically inclined, knock yourself up a few timber blocks of 200x50x100mm dimensions and pop down to the dealership to do it yourself.

Have you ever had trouble with boot measurements? Tell us about it in the comments below.