Mind your Cs and Fs

detail from Linnaeus Hortus Cliffortianus frontispiece, Wikimedia Commons

detail from Linnaeus Hortus Cliffortianus frontispiece, Wikimedia Commons


I know that people sometimes warn you to mind your Ps and Qs, but currently I’m preoccupied with my Cs and Fs. Another way to express this is, “how hot is it, really?

I grew up knowing that temperature could be expressed in various ways, but the only one that comes automatically to my mind is Fahrenheit. Mention a temperature using that scale, and for me there’s no time lag between hearing the number and understanding the point. If you tell me that the temperature dropped to 25° F last night, I know that your garden lettuces are probably history. If you say that the forecast says 76° F for our outing tomorrow, I know my sandals will be fine. If you tell me to preheat to 450° F, I know we’re likely to be making pizza and not banana bread.

This assumed knowledge has been handy for many years, but it’s not doing me much good now, as I’m no longer in Fahrenheit Land. It turns out that very few of the world’s people still live there.

Countries still using Fahrenheit, modified from Wikimedia Commons

Countries still using Fahrenheit, modified from Wikimedia Commons

Here’s a map that shows you who uses the Fahrenheit scale. It’s missing a few island dots, like one for Jamaica–I wasn’t sure I could make them visible (you can hardly see Belize as it is). But you can use your imagination to put in one for Palau, a tiny speck in the Pacific Ocean. Draw a line due east of the southern tip of Vietnam, and where it intersects the north-south line that divides Australia in two, you’ll find those folks (whichever of the 20,754 who care to chat with you) talking about their tropical temps in degrees F.

While the history of the development of these two scales is interesting, I’ll tuck it at the end*, and get on to the everyday matter of “getting to Celsius.” Or perhaps I mean hearing Celsius, translating to Fahrenheit, and getting to understanding. In my experience, you don’t really get comfortable in speaking a new language until you stop thinking in your first language. At some point I’m going to need to cut out the middle step of consulting my inner Fahrenheit. For now, though, I need to be able to step over to it quickly and get my bearings.

I have already quilted the two scales together at a few points in terms of baking temperatures; I know that 375° F is pretty close to 190° C, and I can work with close. My oven dial is really imprecise, and I’m guessing that even if the dial were larger with more tick marks, the oven itself has about 3 temperatures: meh, hottish and blast-furnace, so more precision would be wasted on it.

Still, a person likes to know, so I’m working on a practical way to connect the scales. I have looked up the formulas for getting from one to the other before, and can generally remember that the fraction 5/9 features, but it hasn’t settled comfortably into my head. I’ve seen a shortcut method that looked appealing, but once I looked carefully it seemed too far off to be useful. I’m better at remembering things when I’ve made them my own, somehow. Here’s what I’m trying currently.

We can line the two scales up at the freezing point: 32° F matches 0° C. Now, for every 5° increase in C, I’m going up 9° in F. That’s easy addition, just going up ten and down one. So 5° C = 41° F. So far, so good. If we keep on this way, it looks like this:

F          C
50 = 10
59 = 15
68 = 20
77 = 25
86 = 30
95 = 35
104 = 40

That’s about as high as most humans should have to figure air temperatures–last summer visiting el Guapo’s parents in Southern Utah we got to 45° C (113° F), but I wouldn’t recommend trying it yourself.

I think we can skip those intervening temperatures and just review the range relevant to baking. I’m guessing that most of what we’re likely to bake involves temps between 300° and 500° F, and recipes generally give instructions in increments of 25 (if you’re making candy, a few degrees can make the difference between a ball and a crack, or success and disaster, but in that case, your thermometer probably has markings for both F and C). As it turns out, a 27° increase in Fahrenheit is a 15°  increase in Celsius, and that’s close enough to work for me. The table looks like this:

F          C
293 = 145
320 = 160
347 = 175
374 = 190
401 = 205
428 = 220

I don’t have any recipes that call for preheating to 293° F, but given the precision of most ovens, it’s close enough, and allows me to stick with the 15° increments in the Celsius column. Just about everything I bake can be done at one of these nice round Celsius temps, and I’ll bet if I tape this little list to my cupboard, I’ll have it learned quickly. If you don’t want to tape things to your cupboard, your search bar will give you what you ask without delay; just type in this form: [number] F = C and out pops the Celsius figure.

I’m managing to get our pizza, banana muffins, and Arroz al Horno to the table without significant mishap, so the conversion thing is going well enough. And when it comes to air temperatures, I don’t have to consult a thermometer, in either C or F. After all, we’re in Valencia. It’s going to be a lovely day.

photo by el Guapo

photo by el Guapo

*The Celsius scale was first established in the 1740s, and is named after Anders Celsius (1701-1744), the Swedish astronomer, physicist and mathematician (that sort of thing used to be allowed). He called the scale centigrade, Latin for 100 steps. (Strangely, he originally proposed 100 degrees as the freezing point and 0 degrees as the boiling point, but it wasn’t long before that arrangement was reversed.) The term centigrade stuck around until 1948, but because the word was also used in both Spanish and French to refer to measuring angles, there was a movement to sort it all out somehow. The Comité International des poids et mesures (CIPM to its friends) decided to weigh in (see what I did there?) and decree that “degrees Celsius” was the way it would be…except where it wasn’t. And so to the contemplation of Fahrenheit.

The Fahrenheit Scale takes its name from the physicist Daniel Gabriel Fahrenheit (1686-1736), who initially proposed setting 0 degrees as the temperature of a mix of equal parts ice, ammonium chloride and water, and setting 100 degrees, so the story goes, at “blood heat,” as represented by the temperature of his wife’s armpit. After various adjustments, things settled down eventually so that 32° F was the freezing point of water, and 212° F was its boiling point, at least at sea level.







2 thoughts on “Mind your Cs and Fs

  1. You write about the “darndest” things, Daughter of mine!! Interesting-but I hope we don’t convert over before I die. In the celestial kingdom the weather is bound to be Valencian, don’t you think?

    • Aw, you’d be fine–you’ve always been a quick study. If I made you a little list for your cupboard, you’d be baking in Celsius by dinner time tomorrow! And I would not be at all surprised in Heaven sets its weather to match Valencia….

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