Talk:Gallon

From Academic Kids

I get dissy reading this page... how can civilized western nations in the 21st century NOT use the SI-system?

History

"The metric definition of exactly 4.546 09 L was adopted shortly afterward."

I don't know that this has ever been officially adopted as the definition, anywhere. But it certainly is at least quasiofficial in at least the U.K. and Canada, a conventional conversion factor that has probably been at least declared to be good enough for legal purposes. Note that some lists of conversion factors such as The Units of Measurement Regulations 1995 (http://www.hmso.gov.uk/si/si1995/Uksi_19951804_en_2.htm) of the U.K., do not claim to present any new definitions, but are rather merely compilations based on preexisting law. If you take them as official redefinitions, then the U.K. must have a weird definition of the hour, with a nautical mile defined as 1853 metres and a knot defined as 0.51477 metres per second (the actual legal definition of that nautical mile remains 6080 feet, notwithstanding the Units of Measurement Regulations 1995—note that the corresponding values for the international nautical mile are 1852 m and 0.51(4) m/s with the part in parentheses repeating, fours forever, no sevens to be found).

However, this statutory instrument may well be the one in which the 4.54609 litres became the quasi-official value for the United Kingdom. Before that, and going back into the 1970s at least, this value had been at least quasi-official in Canada, but the quasi-official value in the U.K. was different: 1 gal = 4.546092 litres. This distinction between a Canadian gallon and a U.K. gallon can still be found in many online lists of conversion factors, and in conversion programs which can be installed on computers.

Australia and New Zealand and other places may have similar lists of conversion factors in association with their metrication, but I don't know exact values, official status, or effective dates.

Gene Nygaard 05:50, 31 Dec 2004 (UTC)

NIST gives 4.54609 L/gal as the exact conversion factor for both the "UK and Canadian" imperial gallon(s) (Ref: Guide for the Use of the International System of Units (SI) - NIST Special Publication 811). The Canadian definition matches this and can be found at Weights and Measures Act, R.S. 1985, chapter W-6 (http://laws.justice.gc.ca/en/W-6/text.html). Dunno about the UK. I've never seen the ...092 definition.

Urhixidur 15:32, 2004 Dec 31 (UTC)

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Re the 1963 U.K. definition given here:

"In 1963, this definition was refined as the space occupied by 10 pounds of distilled water of density 0.998 859 g/mL weighed in air of density 0.001 217 g/mL against weights of density 8.136 g/mL."

Were these densities actually per millilitre, or were they per cubic centimetre? Note that the two were not the same thing in 1963. Gene Nygaard 05:55, 31 Dec 2004 (UTC)

Ambiguous gallons in 'mpg'.

Many articles mention 'mpg'. This is ambiguous. What do people think is the best way to disambiguate this? For example we could say:

• 15 US mpg
  I think this is the 'least bad' solution.
• 15 mpg (US)
  I would prefer this solution because the 'US' is put near the gallon. Unfortunately, the context often requires more parentheses. For example 15 mpg (US) (16 L/100 km)
• 15 mi/USgal
  Hmm

Thoughts welcome. Please look at article examples to see how this would work in practice. Bobblewik  (talk) 12:55, 20 Jun 2005 (UTC)

• 15 mi/U.S. gal
• 15 mi/gal (imp)

If in running text, not just in tables, "miles per imperial gallon" or "miles per U.S. gallon" in first instance, and one of the abbreviated versions thereafter.

If any of them should happen to be used with boats or aircraft, ambiguous miles maybe should be disambiguated as well. I don't see that as much of a problem and can't think of any place where that happens now in Wikipedia, just throwing it in for completeness.

Symbols for units of measure should never be italicized, and your use of italics is unclosed. Gene Nygaard 13:34, 20 Jun 2005 (UTC)

I think we can assume US gallons for any contemporary context and only disambiguate the other cases. Actually it is just yet another reason not to use English measures at all. Christoph Päper 14:24, 20 Jun 2005 (UTC)

I've heard that many of the British still use miles per imperial gallon, though they buy their petrol by the litre. Their odometers are still in miles, anyway, so litres per hundred kilometres isn't any easier to calculate. It's even weirder in Canada, where I know many people who buy their gasoline by the litre and whose odometers are in kilometres still figure miles per imperial gallon. Gene Nygaard 05:16, 21 Jun 2005 (UTC)

The imperial gallon is still used when 'mpg' is quoted in Britain. As far as I know it is the dominant unit that British people use when discussing fuel efficiency even though fuel is sold in litres, not gallons. Manufacturers still quote it, for example Ford UK says the Focus does 8.7 L/100 km (32.5 mpg). Furthermore, in-car fuel efficiency displays quote 'mpg' and mean the imperial gallon. Many British readers assume that 'mpg' refers to the imperial gallon because they are not aware of any other gallon. I suspect that the same would apply in other countries. Bobblewik  (talk) 10:40, 21 Jun 2005 (UTC)