Help with a rather long sentence?

[MasonXY]

I brought some books back from Japan, and was planning on translating them myself, but I've run into a few trouble sentences. This one in particular stumps me.

サイズが少し大きいのは身長が伸びることを前提に買ったにもかかわらず、予測ほど背が伸びなかったからだろう。

The previous sentences were describing a character wearing headphones and a shirt. With my limited knowledge of Japanese, I understand the words and what they might be trying to say, but I am not certain.

Certain particles such as のは、にも、 and だろう confuse me as well.

 

[Majestic]

What do you think they might be trying to say?

Not trying to be annoying, but just want to see if you are on the right track and where to help.

 

[lanthas]

のは: nomalizer の + topic は. So, the topic of the sentence is the fact that the サイズ [of the shirt] is 少し大きい.
にもかかわらず: fixed expression
だろう: informal version of でしょう

 

[MasonXY]

What do you think they might be trying to say?

Not trying to be annoying, but just want to see if you are on the right track and where to help.

From what I get from it, its talking about the shirt, being slightly big, and stretched because the character's body is tall and stretched looking? And something about him buying the shirt? Again, I don't know.

 

[lanthas]

Let's break it down. At the highest level, the structure of the sentence is this:
...は ...からだろう。
"Concerning ..., it's probably because of ..."

The first part is easy: サイズが少し大きい, the size [of his shirt] is slightly [too] big.

The next part explains why this is probably the case:
...にもかかわらず、...ほど背が伸びなかった
"Irregardless of ..., his stature didn't lengthen to the extent of ..."
or more naturally:
"Irregardless of ..., he didn't grow as much as ..."

Irregardless of what didn't he grow?
身長が伸びることを前提に買った
"Bought [the shirt] with the assumption of his body height lengthening"
or, more naturally
"Bought the shirt assuming that he would grow (into it) (in the future)"

What is the extent to which he didn't grow? 予測. So, he didn't grow as much as (his own) prediction. In other words, he didn't grow as much as he thought he would.

Now you should be able to come up with a natural translation of the complete sentence.

 

[MasonXY]

Let's break it down. At the highest level, the structure of the sentence is this:
...は ...からだろう。
"Concerning ..., it's probably because of ..."

The first part is easy: サイズが少し大きい, the size [of his shirt] is slightly [too] big.

The next part explains why this is probably the case:
...にもかかわらず、...ほど背が伸びなかった
"Irregardless of ..., his stature didn't lengthen to the extent of ..."
or more naturally:
"Irregardless of ..., he didn't grow as much as ..."

Irregardless of what didn't he grow?
身長が伸びることを前提に買った
"Bought [the shirt] with the assumption of his body height lengthening"
or, more naturally
"Bought the shirt assuming that he would grow (into it) (in the future)"

What is the extent to which he didn't grow? 予測. So, he didn't grow as much as (his own) prediction. In other words, he didn't grow as much as he thought he would.

Now you should be able to come up with a natural translation of the complete sentence.

Thank you! That makes more sense to me now!