Logical it isn't, and it is about to get worse. From Sunday 1 October, in line with a 1989 European directive, all shops are obliged to sell prepacked goods in metric measurements - on pain of a $5,000 fine, and imprisonment for non-payment.
So is this the end of British imperialism? Apparently not. Shops will still be able to sell loose goods, such as fruit and vegetables, in pounds and ounces until the turn of the century. And your doorstep pint and half of draught are exempted indefinitely, as are quaint quantities such as fathoms and therms. Evidently, some aspects of British culture remain sacrosanct.
What exactly is the Government doing to help the metrically-challenged on M-day? Not much, it seems. Most of the major supermarkets have produced leaflets warning customers of the forthcoming conversions, but government campaigns are conspicuous by their absence. Even the Consumers' Association has maintained a curious silence. The more cynical might accuse the Government of sneaking metrication past us on the quiet to quell the Euro-rebels. The Department of Trade and Industry, however, denies Euro-compulsion. Metrication has been on the agenda since 1965, it argues, and 80 per cent of groceries are already sold in metric measures.
Yet organisations like the National Consumer Council (NCC) and the Institute of Trading Standards Administration (ITSA) think the Government should have introduced more radical changes.
"We should have gone metric in a big bang," says the NCC's deputy director, Robin Simpson. "We've faffed about for 20 years and it's just silly to give in to cultural prejudice and not to do the whole thing in one go. The British can cope - they do well enough when they cross the Channel."
Those thrown into confusion at the cheese counter in French hypermarkets might not agree, but, sentiment aside, metrication has significant benefits. It makes the export of British goods less cumbersome, and in the long run should make life easier for shoppers. Some of us, for instance, still hit mental paralysis when it comes to remembering the number of ounces to the pound and pounds to the stone (16 and 14, I think). And all but the most hardened imperialist would agree that 100 pence to the pound is a lot easier to get your head around than 240.
But change never comes cheap. According to the DTI, 62,000 British companies have already spent pounds 32m coming to terms with metric conversion. These costs to cope with legislation all too often end up coming out of consumers' pockets. Ultimately, however, the real losers are likely to be small shopkeepers, with fewer resources to cope. A small local shop, for example, may have to pay around pounds 150 to have scales recalibrated, and from pounds 1,000 to pounds 1,500 for new ones. Any price hikes would drive customers deeper into the arms of superstores.
"It's all right for the Sainsbury's and Tescos of this world, which have sufficient means to take it in their stride," says Alan Street, chief executive of ITSA. "The ones who will squeal most are the smaller traders who find the costs of metrication quite heavy."
To most consumers, M-day will probably pass much like any other, but for those with a more nostalgic turn of mind, it will be a watershed. For units of measurement are more than cellophane-deep. There is something, perhaps, in the Euro-sceptics' talk of cultural heritage. After all, when parents proudly announce the birth of their 4,500g baby, will you be filled with tenderness?
Getting the measure of metrication
Loose or unpacked goods such as cheese, vegetables or fruit can still be served in pounds and ounces; if they are wrapped in cellophane, you will be paying per kilo.
Milk will arrive on your doorstep in pints, but sit in metric cartons on the supermarket shelves. While landlords can still pull a pint of best draught bitter, your bottle of lager will be in centilitres.
Fabric can still be sold by the yard, but you will pay by the metre; carpet can only be sold by the metre.
Some imperial measurements are deemed "descriptive" and therefore exempt from metrication, so you will still be able to purchase a 16in-collar shirt, a 3.5in computer disk or a yard of packaged electrical flex.
Miles are here to stay for the foreseeable future, and an acre will still be an acre for the purpose of land registry.
Full fathom five will still hold true for mariners, and gas measurements will remain in therms.