What formula switches from pints to milliliters?

Factual Questions
61

If you want to convert a figure from pints to millilitres and give an answer to six decimal places then you had better be able to demonstrate that:
[ol]
[li]When you measure a pint what you get is a pint and not, say, 1.000001 pints or 0.999999 pints, and[/li][li]When you use your millilitre conversion, you can in fact measure to the nearest nanolitre. Don’t forget to allow for evaporation and for the liquid clinging to the measuring vessel by surface tension.[/li][/ol]

There’s a reason why people are suggesting rounding, and it’s not because they are incapable of multiplying decimals accurately. If I quote my home to work distance as 50 miles, it’s foolish to Google that “1 mile = 1.609344 kilometres” and conclude that I will drive home exactly 80.4672 km.

62

Exactly. Thank you for saying it in short enough paragraphs that maybe it’ll finally sink in.

The result of a conversion cannot be more precise than the measurement or specification of the input value. Sure you make the math include more digits and the display of the output value contain more digits, but the validity of all that extra apparent precision is nil.

Including false apparent precision is worse than meaningless; it’s actively misleading.

63

And I repeat, that with recipes it’s the relative proportions that matter more than the actual quantities. The weights or volumes are needed to give the right quantity or size of finished product, but it would be perfectly valid to say, as I see in my mother’s recipes, *“Equal amounts of flour, sugar and butter. Tsp of vanilla and 1 egg.”

That leads me to another point - who actually weighs an egg before using it? A good cook will use whatever they have and add sufficient other liquid to get the correct consistency. All kind of variations exist between flours, fats and sugars.

Oh - and if, as an American, the oven temperature is 350 F should I try to set my European oven to 176.667 C?

64

I’m think you’ve gone overboard in your protest against over-precision.

The people who sell the egg weigh it. The standard sizes actually mean something. This has already been covered in this thread. Most baking recipes that call for eggs are calibrated for large-size eggs. Yes, there is some variation within each size grade. That level of variation is acceptable for most recipes. The level of variation between size grades is unacceptable for many recipes.

Also, your recipe of “Equal amounts of flour, sugar and butter. Tsp of vanilla and 1 egg” does not guarantee relative proportions. With this recipe, you could have one pound each of flour, sugar and butter, or five pounds each, in combination with one egg and a teaspoon of vanilla. The reason your mother’s recipe is written this way is that she had an idea in her head of how much flour, butter and sugar should go with one egg to make the particular product, but she didn’t write it down. There was a time when recipes were given with no measurements at all because cooks were supposed to know through experience what proportions were reasonable. Most people don’t cook this way any more, especially when baking (when precision in measurement is actually important).

65

A bizarre idea. It’s wrongheaded, if the book is to be sold to cooks or people who like to read cookbooks.

SD GQ readers, perhaps.

My point exactly.

Honestly, this sounds like a whoosh. In 2016. Conversion sites with food densities are abundant.

[/QUOTE]

66

We omit here the story of the museum caretaker and the dinosaur skeleton that was 175,000,013 years 6 months and 22 days old.

67

I don’t understand why so many of the readers of this thread seem to have missed two points I have made repeatedly, which are (1) the recipes use normal-precision U.S. traditional units just as you see in any other U.S. cookbook and (2) even the spreadsheet allows for output to 1 or 2 significant digits in fractions or to 1 or 2 significant digits in decimal.

To pick on Your Great Darsh Face as a representative of the contributors who still want to convince me that there’s a limit to how much precision is needed, YGDF, you say, “If you want to convert a figure from pints to millilitres and give an answer to six decimal places . . . .” But I don’t. I don’t want to convert anything to six decimal places, or even three decimal places. You have set up a Straw Man, and you’ve successfully knocked him down, but that doesn’t change the fact I never disagreed with you. You keep bashing away proving a point no one disagrees with and never did.

You say, “There’s a reason why people are suggesting rounding . . . .” My question is simple: What is it you and other people are suggesting I round? LSLGuy keeps saying I should round, but he too won’t tell me what it is I should round, even though I asked him straightforwardly twice before.

68

My assumption all along has been that you would present a recipe with ingredient list completely in US customary units, and then the same recipe restated into entirely metric units. It seemed to me that anything less is meaningless in the context of a recipe.

Given that mission, I believed you’re going to need some way to have all the units be easy to measure in either system. IOW, I think you’re going to have to round in a way that preserves two partly conflicting goals: ease of measurement for every ingredient, and 2) correct proportionality between the ingredients.

If I’ve misunderstood your goals here, I’m sorry.
As a separate matter, I’ve been harping on the idea that no matter the topic, an output number of a conversion calculation can’t be more precise than the input number was. Regardless of whether you’ve recognized it yet, when a recipe says “1 cup carrots”, that does NOT mean “1.0000000 cups carrots”.

It really means something between “1 (+/- 0.05) cups carrots” and “1 (+/- 0.25) cups carrots”. Only by learning a lot more about cookbooks and recipes can you make an intelligent analysis of what the original recipe’s tolerances actually are. And once you have completed that analysis, then you can correctly apply the same tolerances to the result of converting “1 cup” to 236.5882365 milliliters or whatever unit.

If you don’t do all that, you’re guilty of using correct arithmetic to produce an incorrect (or at least invalid) real-world result.

69

LSLGuy, you say, “My assumption all along has been that you would present a recipe with ingredient list completely in US customary units, and then the same recipe restated into entirely metric units.” That would be a lunatic waste of a lot of space, which is probably why I have never seen a cookbook like that. Have you? What made you think such a strange thing for so many replies to me, especially since I specifically gainsaid any such assumption several times?

You say “an output number of a conversion calculation can’t be more precise than the input number was.” Here again you’ve proved something no one ever disagreed with. Why did you bother to point out such an obvious fact?

“1 cup carrots” does TOO mean “1.0000000 cups carrots.” That’s math, and you know it, so can you tell me why you say the opposite?

You say I’m “guilty of using correct arithmetic to produce an incorrect (or at least invalid) real-world result.” First of all – as you seem to have forgotten so I’ll say it a FIFTH time – nowhere in the recipes do I do that. Nowhere in the recipes do I convert anything from US units to metric or vice versa. Why can’t you seem to understand this simple fact?

But no, correct arithmetic can never “produce an incorrect real-world result.” That’s by definition of the term “correct arithmetic.” The result might display useless precision, but it’s still the best possible number with that much precision, which is the opposite of “incorrect.” Why would you say otherwise?

Similarly, the result of a number derived from correct arithmetic, even if carried to uselessly extreme precision, is the opposite of “invalid.” Indeed, the result is the very definition of valid in that no other number with that many decimal places is better. Why would you say the opposite? (I remind you it was you who postulated this extreme degree of precision, not me.)

Adding the adjective “real-world” to the noun “result” doesn’t change anything you said about using correct arithmetic. It’s still wrong with respect to the word “incorrect” and the word “invalid.”

If all you’re saying, LSLGuy, is that the amounts of ingredients in recipes may be adjusted up or down, any dolt, including me, knows that. Sheesh.

I was and still am looking for criticism of the paragraphs explaining how I arrived at the figure of exactly 3,785.411784 mL per gallon, which informs many of the cells of the spreadsheet. Here they are.
"In Case You Care

"Here’s how you can arrive at the magic number of exactly 3,785.411784 milliliters per gallon, which is a number that lets us move from traditional U.S. units to metric and back.

"(The letters mL mean milliliters, i.e., one thousandth of a liter. The letters cm mean centimeters, i.e., a hundredth of a meter. All the numbers below are exact to the very last last decimal place except the very last number, which is precise to only 15 decimal places.)

"1 US liquid gallon = 231 cubic inches (given, per NIST)

"1 inch = 2.54 cm (given, per NIST).

"Therefore 1 cubic inch = 16.387064 cubic cm (from 2.54 cm/inch of height * 2.54 cm/inch of width * 2.54 cm/inch of depth). If there are 231 cubic inches per gallon and each cubic inch is 16.387064 cubic cm, then the product of those two numbers is the answer we’re seeking, which is the number of cubic cm in 1 gallon of water, which because 1 cubic cm is equal to 1 mL means the magic number is 3,785.411784 mL in one gallon. The formula for your calculator or spreadsheet is 231 * (2.54^3).

"All the other traditional U.S. units such as tablespoons and pints can be calculated based on the gallon, which is what this spreadsheet does, so now that we know how many mL are in a gallon we know all the other units as well.

“(The reciprocal, if you need to convert from mL to gallons, which is 3,785.411784 raised to the power of -1, is pretty close to 0.000264172052359 if I typed it right, in case you care.)”

O Straightdopulists, how can I improve the seven paragraphs above, first as to facts and second as to clarity?

70

Johnegee, this is the crux of your misunderstanding here. Unless you are in a clean room CPU lab trying to make ultra-pure silicon or something, no number ever used by a human is precise to the 7th digit. Even in semiconductor labs, I think “five nines” or 99.999% pure is precise enough. Nobody but serious chemists use numbers of that precision. Rocket scientists don’t even care about the tolerance of their machine parts to that kind of precision.

So kitchen cooks definitely don’t. As LSLguy said, when a cook or recipe says “1 cup” they really mean “somewhere between 0.75 and 1.25 cups”. Bakers might mean something more like “between 0.9 and 1.1 cups”, but zero recipes written or used in the history of mankind mean “1.0000000 cups – no more, no less”. So, no, “1 cup” does not mean “1.0000000 cups”. Ever.

So to presume that “1 cup” in a US recipe means “236.5882365 ml” in a metric recipe isn’t just “useless precision”, it is wrong.

If all you are doing is making a spreadsheet for exact conversions between units, then those paragraphs are fine. What you’ve made is a calculator.

However - and this is a fundamental aspect of what it means to do math with real world objects - the calculator is wrong. Unlike a slide rule, which has its own limited precision, an electronic calculator (aka, “computer”) can spit out digits until it is blue in the face. But, depending on the precision of the numbers inputted into that calculator, most or all of the digits that it outputs are wrong.

This is something engineers learn early on. I think we covered it on day one of my freshman “intro to engineering 101” class. After having learned it in high school physics and biology, as well. But don’t feel bad, most people’s education is lacking in this area. Wiki has a decent overview of the subject. There’s also this:

What your calculator spreadsheet is doing is calling hundred-million year old dinosaur skeletons “100,000,005 years, 13 days, 4 hours, six minutes and 27 seconds old”. And that isn’t just needlessly precise, it is completely incorrect.

EDIT: Totally forgot this was a two year old thread. Whoops! :smack:

71

Well, one year, four months, and 13 days old, anyway.

72

I started reading this thread thinking, “what spammer bumped this thread? and how did this one get picked to begin with?” HOwever, I am glad that I made it to the end… this made it worth the read.

73

Now. For one-day resolutions of “now”. :smiley:
@DrCube: Your revival isn’t a total goof. After 16ish months’ absence the OP of this thread started a new thread just yesterday on a closely allied topic. http://boards.straightdope.com/sdmb/showthread.php?t=819199

Apparently his *magnum opus *cookbook and spreadsheet remains a work in progress. But it’s getting better every day.

74

I would only use pint to refer to liquids, stick to 473mL per US pint (16 US fluid oz) and 568mL for a British/imperial pint. But I would also try to round to something you can measure with common cooking equipment – using a measuring cup or 1/4,1/3,1/2 cup measures, or tsp/tbsp for smaller amounts – having exact amounts (even without decimals) will just annoy most cooks, even if they know a lot of math.