It is confusing for every paper. Here's Rose Wild of The Times's Feedback column:
One of the longest entries in The Times Style Guide is headed, simply, "metric". The heading is more or less the only simple thing in the entry, as is hinted at in the opening advice: "The Times should keep abreast of the trend in the UK to move gradually towards all-meteric use, but given the wide range and geographical distribution of our readers, some continuing use of imperial measurements is necessary."
It might have mentioned the wide range of our writers as well, but the important message is clear: "The main aim is to avoid confusing the reader."
The article continues delving into the issues of rainfall...Nelson's column and the wide variety of buses operating in London. But it concludes:
I'll leave this subject for now with a charitable theory from Francis Wood. He suggests the problem arises "because those providing the translations are young, and have grown up knowing only the metric system, whereas my generation grew up using the imperial system every day but needing to know metric units for school science."
(Times Feb 25, 2012)
See it's confusing, which is why we should be sensible about it. Returning to petrol talk about it in litres - unless using it for historical comparison (or to get shock value - go on check it).
But then we have the 100m sprint - there is no need to convert it you would just look idiotic calling it the 328 feet 11⁄64 inch sprint.
And when we talk about drinks we refer to pints (yes, even wine for the ladies).
But generally areas relating to height and width - now given as metres as standard in planning documents - should be converted. So too space. Any examples of kilometres into miles and so forth.
Yes it does take a bit more time but people will appreciate it.