this=3 that=1
This room is three times larger than that one.

This room is three times as large as that one.
表示的是同一个意思

用的倍数都是3倍。larger than 和as large as，as和as之间只能夹形容词，而且第二个as后面要跟名次
twice the size of 是固定结构。

若将条件稍作修改：if the size of this room is 3 (units),the other is 1(units),then "多“2倍”" may be expressed in English as such: 1）This room is three times as great as that one. 2) This room is three times as greater than that one. 3) This room is three times the size of that one.
以上均可译为“是---的三倍”或“比---多二倍”
倍数的总结
A is n times as great（long，much，…）as B.（①） A is n times greater （longer， more，…）than B.（②） A is n times the size （length， amount，…）of B.(③) 以上三句都应译为；A的大小（长度，数量，……）是B的n倍[或A比B大（长，多，……）n-1倍]. Eg. This book is three times as long as （three times longer than，three times the length of ）that one. 这本书的篇幅是那本书的3倍（即长两倍）。 注：当相比的对象B很明显时，than（as，of）B常被省去。