I have a recipe that calls for "6 large baking potatoes." So the question becomes, what is considered the average size of a large baking potato? I've looked online, but sadly do not have time to continue my search and the results appear to be all over the place.
Tough question - there are a lot of non-scientific ways to measure small/medium/large potatoes and nobody seems to agree on exactly what weight each is. However, there are a few ways I identify large vs medium at home.
In my experience, a large potato is about the size you would get in a restaurant (I know, not very specific). That is, when I cook at home, the potatoes I purchase tend to be medium - round (not oval) and about the size of a tennis ball or baseball. When I'm at a restaurant their potatoes are noticeably larger, and generally more oval shaped it seems (closer to a sweet potato in shape and size), which makes them great for stuffing like for a loaded baked potato. Luckily most of the recipes I have at home that involve potatoes don't require precise measurement, so I just stick with my eyeball measurements and don't even bother weighing them.
I found a source online that says this:
According to Shape magazine, eatbetteramerica.com and prevention, a medium potato is the size of a computer mouse, so somewhat bigger than that.
And I think I can get behind that answer. I'd say your average computer mouse (like, one you would get with a new PC, not a fancy third-party mouse) is about the size of an average medium potato. Another way to eyeball: I'm a 30 year old male with hands that are neither very large or very small. The medium potatoes in this bag are about the size of a loose fist for me. So a large potato would be bigger than either of those things.
As for measurements, I have a bag of medium potatoes and it says they're 5.3 oz (150g) a piece. I weighed one and it was closer to 6.5oz (185g). Based on that I'd say a large potato would be anything over 8oz (225g), pushing as high as 12oz (340g).
I found a way to search online for this info: calories. By searching for "large potato calories" I was able to find pages with weights and measures:
So, in short, it seems like I would consider these good numbers:
- Medium potato: 2 to 3" in diameter, 5-8oz (140-225g)
- Large potato: 3 to 4.25" in diameter, 8-12oz (225-340g)
Below is a picture of the medium potato from my bag, compared to some common household/kitchen items. The gift card is the size of a normal credit card, and the knife is a common steak knife from my utensil drawer. Apparently a medium potato is almost exactly the size of a 1 cup measure!
It probably depends where the recipe originated. My Northern Irish in-laws gave me a recipe for Irish stew that called for 6 medium potatoes, and when I made it everyone complained it wasn't potato-y enough! It turns out that their idea of a "medium potato" is WAY bigger than mine.
When cooking for larger numbers of people, size and weight become important. Since restaurants are now including calorie counts, it makes sense to get a feel for the energy density of different types of food. i.e. calories/gram. For example a search revealed 100g of potatoes had 77 calories or .77 cal/g. For an adult requiring about 2,500 calories per day, this would mean they need to eat 3.25kg of potatoes to meet their calorie needs (all else being equal).
At the low end, with a large potatoe weighing 225g, this would mean they would need to eat 14 potatoes in a day! (if that is all they ate). So, for a recipe calling for "6 large baking potatoes", it would make sense that this would be enough for a half dozen people, eating one of three meals in a day.
Having a small scale in the kitchen can be handy for questions like this, as I find both temperature and weight are difficult to determine by feel alone.