Possible: I’m of average weight. (Sounds better) My weight’s average. (Best) ‘I’m an average weight.’ isn’t natural. I have an average weight. (Ok, but longer for no reason.)

Yes saying 'I'm an average weight' is grammatically correct but to sound more natural you might say 'I have an average weight' or 'My weight is average'

Great question! Let's break down the phrase "I'm average weight" and see if it sounds natural or needs an article. Correct Usage: "I'm of average weight." This is the most natural and grammatically correct way to express this idea. It implies that your weight is typical or within the average range. "I'm an average weight." This sounds a bit awkward and unusual. Weight is generally treated as a condition or description, not an object, so using "an" with it is less common. "I'm average weight." While this is a simpler form, it might sound a little incomplete in formal contexts. However, in casual conversation, it is often used and understood as short for "I'm of average weight." Why "of" Works Best: The preposition "of" links the phrase to a category or description. Similar examples include: "I'm of average height." "She's of medium build." "He's of great importance." Natural Alternatives: If you want to sound more fluent, try these: "I have an average weight." "My weight is average." "I'm at a healthy/normal weight." Conclusion: Correct and natural: "I'm of average weight." Acceptable but informal: "I'm average weight." Less common: "I'm an average weight" (generally avoided). Your Oxford book likely simplified the phrase for learners, making it sound less formal but still understandable!

I hear native speakers say “I am average weight “, but you are right, there may be others that are more grammatically correct. I think it is used because you’re still saying « I am + adjective ». There are many, many ways to say the same thing.

Both "I'm average weight" and "I'm an average weight" can be understood, but they are used differently and have slightly different levels of naturalness: 1. "I'm average weight" – This is grammatically correct and natural in casual speech. It uses "average weight" as an adjective to describe yourself. 2. "I'm an average weight" – This is also correct, but less commonly used. Adding "an" makes "average weight" a noun phrase, implying you're a specific instance of an average weight. It might sound slightly more formal or unusual in conversation. In most cases, "I'm average weight" is the preferred choice.