X times as ～ as ⇔ X times the size of ⇔ X times ～er than

倍数は as ～ as の前に置く。形容詞を名詞に変えると the size / the number / the length of の形になる。「2倍」は twice、「半分」は half as ～ as。

• This room is three times as large as that one.
  この部屋はあの部屋の3倍の広さだ。
• This room is three times the size of that one.
  この部屋はあの部屋の3倍の大きさだ。
• This room is three times larger than that one.
  この部屋はあの部屋の3倍広い。

X times larger than は日常では使われるが「3倍大きい＝4倍？」と曖昧になりうるので、正確さが求められる英作文では as ～ as か the size of が安全。グラフ問題では the number of と組んだ形が頻出。