Monday, July 18, 2011

Answer to our Friday Fermi Problem: Eating the Iron Skillet

Here's our answer to the Fermi problem we posted last Friday . . .

The typical recommended daily allowance of iron is about 15 milligrams/day.

A 12 inch skillet weighs about 3 kilograms.

So a single skillet could provide a single person with 3000/.015=200,000 daily doses of iron before the pan is entirely consumed.

But a pan isn't very useful once enough of it is so worn away that it won't hold your eggs any more, so let's assume that you can only eat up about 1/5 of the pan before it's no good.

That means you can get your daily iron fix from a single skillet for 40,000 days, or 109 years if you use it every day.

There's a good chance, however, that the skillet is not just for you, but for a group of people like a family. The typical family has about 4 members. If they all get their daily iron from the same skillet, the pan would last about 109/4 = 27.25 years.

At least one cooking site claims that iron skillets will last a lifetime. If you define a lifetime as 75 years, our estimate suggests that they may be stretching the truth a bit. On the other hand, it's unlikely that anyone is going to use the same pan to cook family meals every day.

In other words, an iron skillet almost certainly will last a lifetime, but probably not much more.


  1. You are basing how long it will last on the RDA. Who says that we eat our RDA in iron when we cook with a skillet? Obviously we don't. So an iron skillet will probably last a lifetime and much more.

  2. I'm basing the calculation on Vanna's claim that food cooked in a skillet is a good source of iron. If it doesn't provide something close to the RDA, then it's not a good source of iron. Therefore, if we accept Vanna's premise, we have to estimate that it provides roughly the RDA of iron.

    Of course, she could be wrong.

  3. Heh ... one suspects that the necessary steady diet of fried food would cause the skillet user to expire long before the skillet ...