Posted May 17, 2012 By Presh Talwalkar. Read about me , or email me .

I recently started eating egg whites regularly, and that meant I needed to start shopping for eggs every week.

My local grocer sells a variety of egg sizes. Can you figure out which one is cheapest?

Here are the prices:

Here is how I approached the problem.

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Step 1: get the weights

To solve the problem, one needs to find the weights of the various sizes.

In my case, the weights were actually written on the egg cartons. But if they weren’t, I could have looked up the USDA regulations on egg sizes to find the following weights.

Step 2: compare unit costs

Now we can attack the problem. We will divide the cost by the weight to figure out the unit cost of each egg size.

It is clear from the table that eggs slightly decrease in unit cost the larger the size.

It’s not a big change: the jumbo sized eggs are roughly 3 percent cheaper than the medium sized ones. Still, this value adds up because I buy eggs almost every week.

Step 3: consider yolk:white ratio

There is one extra consideration. The unit cost is the appropriate measure if I were eating the entire egg.

But clearly I am going to throw away the shell. And as is the case, I typically throw the yolk away and just eat the whites.

If the extra weight from the larger eggs were due to the increased shell size or yolk size, then the larger sized eggs would not make sense.

So the question is: do the larger eggs contain more egg whites to make it worth it?

(Incidentally, buying eggs and throwing away the yolk is also a lot cheaper than buying products that only contain egg whites)

I did a bit of searching and luckily found a research paper on exactly this topic of the ratio of egg yolks and whites–it’s amazing the amount of information out there.

It turns out that the weight of the contents in an egg are proportional to its size. As a general rule of thumb, an egg’s weight is roughly 11 percent due to its shell, 31 percent from its yolk, and 58 percent from the white.

This means that egg white will increase proportionally with the egg’s size, and so the jumbo eggs are still the cheapest in unit cost.

Here are the numbers to confirm that jumbo eggs are still cheapest in terms of an egg-white only basis.

Conclusion

At these prices, it’s best for me to buy the jumbo eggs.

In general, one can compare the unit cost of egg sizes to figure out the best deal. This is true even if you care only about the egg whites or yolks, because both typically increase proportionally with egg size.