The precise way to easily convert from Celsius to Farenheit is:
Assume we have a temperature reported as 26 °C
Double that number = 52
Subtract 10% of that = 52-0.1*52 = 52-5 = 47
Add 32 = 47 + 32 = 79°F
Notice that the numbers are rounded off to the nearest degree.
Do this for minus 40°C and you will find that -40°C = -40°F. Try it.
Unfortunately, going from F to C is not quite that easy.
Probably because thermometers which read in Reaumur are very rare in the US, which is the only place where anyone cares about Fahrenheit.
My God. Could you imagine the horrors?
and is particularly important in the cases of deci- and Deka-, pico- and Peta (and if you really want to go to extremes, yocto-/Yotta- and zepto-/Zetta).
But my car gets 40 rods to the hogshead.
Looks like it might even be weirder than that:
So beer is sold in pints, but mix it with lemonade to make a shandy and you sell it in metric. 
And gills? Really?!
You’re not going crazy; they are. 
They use imperial gallons for fuel efficiency in car advertising here in Canada as well (and we buy gas by the litre). It’s confusing because when I think of a gallon, I usually think of a US gallon, so when I see “50 mpg highway!” I am impressed, until I realize that it translates to closer to 40 mpg US.
Plus when you go to a bar, if you order a pint, you could get a US pint (16 ounces), a British pint (20 ounces), or occasionally a bastardized pint (18 ounces). Madness! How did the disconnect between UK and US units of volume originate, anyway?
Puerto Rico:
Road distance signs and markers: km
Speed limits and car gages: mph
Fuel sold by: liters
Land measure: small lots, square meters; but NOT hectares, the large measure is a Spanish imperial unit, the “cuerda” (slightly less than an acre).
Interior floorplans: divided, metric and sq.ft.
Body dimensions and weights: US units
Body temperature: Celsius
Weather temperature: Fahrenheit
Dry goods: US units
Hard liquor and wine sold by: metric
but taxed by the: gallon!
Beer sold by: US units
Soft drinks: metric
Milk: ounces/quarts/gallons
Horse track: under a mile: meters
Horse track: over a mile: miles and furlongs
Most of the time we just take a good guess…
It is all way beyond ridiculous.
I really don’t get why it can’t all be metric.
Applying metric measure here and there apparently randomly is too stupid for words.
Apparently, there is something about metric that just doesn’t meet people’s real-life needs, forcing them to supplement it in various ways.
In this age of automated computation, the whole base-10 thing is far less compelling.
But god forbit it is a half liter (16.9 ounces). And if you take a bastardized pint glass and add too much foam so that it’s got 16.9 ounces of beer, then by god the coppers will have your arse in a jiffy while asking if you’re having a laugh.
Just Burma as far as I know. And Canada.
No wait Canada switched to the metric system because they thought the U.S. was.
The U.S. passed a law to convert over to the metric system back in 1975. Even created the U.S. Metric Board to help with the implementation. Due to political opposition, the whole metricization effort was made voluntary, and the U.S.M.B kept complaining about the lack of political clout. In the end, Reagan took away all funding from the U.S.M.B and the effort to convert the U.S. to the Metric system died with it.
However Canada, noticing that the U.S. passed a law, also passed a law in 1975 converting to the Metric system. Unlike the U.S., they actually did convert over.
Just like them Canadians doing what ever the gov’ment tells them to do instead of standing up for their ineligible rights to be completely out of sync with the rest of the world.
(First they came for the inch, but I was not an inch, so I said nothing. Then, they came for the gallon, but I was not a gallon…)
But which metric system? I was taught the centimetre-gram-second Metric system at school but since then, the metre-kilogram-second Système Internationale variant has become standard. It might look like that only requires shuffling decimal points and zeroes around but it amounts to more because some measurements where natural constants are involved have been changed to use others. The most obvious one is the dietary (Khilo)Calory replaced by the Joule with no direct power-of-ten relationship.
For C vs F temperatures, I don’t use a formula or even an informal rule of thumb. Instead, I just memorize a few exact conversions and then mentally interpolate for temps in between.
32 F = 0 C
50 F = 10 C
68 F = 20 C
86 F = 30 C
104 F = 40 C
That covers the temperature range I’m likely to encounter in this part of the world, although elsewhere it may be important to know that 14 F = -10 C and -4 F = -20 C. Also remember that nominal body temp = 98.6 F = 37 C.
Note that my interpolation doesn’t produce a number, it just gives me an idea of how warm or cold it is. For instance, if it’s 12 C, I know it’s a few degrees F above 50, which is a cool day, but not real cold.
The US gallon is also known as the Queen Anne gallon and dates from some time in her reign (which was before we became independent, of course). It was originally defined as being exactly 231 cubic inches, which made one gallon of water be 8 pounds. It’s also a binary system, at least from fluid ounces up through gallon and perhaps beyond. (The computer scientist in me says that binary systems are superior to decimal systems, so take that, SI!)
In the 1820s, the British decided to “improve” their gallon by redefining it as the volume of 10 pounds of water at 62 F (I don’t know if they specified a pressure or not.) No doubt they were influenced by the metric system in their choice of the factor of 10, but that broke the nice binary system they had before. The US, of course, wanted nothing to do with this bastardized gallon (if only because it was British) but I think it was a good decision for other reasons.
Or, it’s just that the switch was so recent that a lot of people who grew up with and are used to the old system are still alive.
Around here, where we switched to metric over a century ago, we have no need for the pre metric units.
Agreed. Pro-metric people talk about how “easy” those units are. “See water freezes at 0C and boils at 100C!”
But who cares? Real life measurements don’t hinge on the boiling point of water. A 0 to 100 F scale which ranges the usual outdoor temps seems to be more practical.
It’s been ages since we’ve had to work with mils in sheet metal. We’ve been 100% metric in sheet metal for years. Thank goodness, and also thank the Japanese and Europeans who are integral to our product designs!
In what respect? As far as I know, my company (a US car maker) is a 100% metric. There are a couple of areas where custom wins over logic (pounds-force, psi), but that’s on the manufacturing floor and something you’d likely never see as a customer. There are, of course, things beyond the car makers’ control that aren’t metric. Tire ratings, distance measurements, and fuel economy, for example.
a measurement scale needs to have fixed reproducible reference points
freezing and boiling are reproducible and very useful points, people take things to the boiling point of water very frequently, maybe even a number of times every day.
in F scale 0 was a particular water ice, water and salt mixture. 32 then was a water ice and water mixture. 96 was human body temperature (the scale was later adjusted).
the C scale originated with better reference points.
for the most part human comfort can use either scale, 1 degree in C is a fine enough gradation.
The only commodities which must be sold in Imperial measure here are draught beer and cider, and milk for delivery by the milkman. Spirits used to be multiples of one sixth of a gill, but were changed a few years ago with little reaction.
Speed limits and distances, heights, widths etc. on road signs must also be in miles/feet and it is illegal to use metric measurement in these cases (though some city councils still try it, whether from ignorance or other motive). The gallon hung on until the price of petrol rose to near £1/gallon, whereupon all the oil companies announced that we had to change to litres because the pumps couldn’t handle it (although now it has gone above £1/litre they don’t seem to have any trouble.) and so the gallon began to disappear from peoples’ thinking.
The speedometer on your car must be capable of reading in mph and it is illegal to operate a car which does not (foreign visiting cars excepted).
I hate the metric system, and will not use it except where it’s inescapable. I also render down metric sums of money into £ s.d., although inflation since the 1970s makes this comparison increasingly difficult (though that’s a different issue and would have happened anyway)