# Saying 'doubled' in Chinese 一倍 vs 两倍

I stumbled upon these 2 sentences:

`这个城市人口比十年前增加了一倍`

`这个城市人口比十年前增加了两倍`

`The city’s population has doubled from a decade ago`

I though `倍` always multiplies the number standing in front of it, it seems like in case of `一`

How come? Is there any logical explanation?

• 这个城市人口比十年前增加了一倍 = 这个城市人口是十年前的两倍, 这个城市人口比十年前增加了两倍 = 这个城市人口是十年前的三倍. May 26 '18 at 18:15
• users suggest suspecting existence at this site of previous discussions of this matter, searching site seems to confirm such suspicion, see esp. chinese.stackexchange.com/questions/9295/… May 26 '18 at 19:27

Technically, when you say "增加了n倍", "n倍" is describing the difference the two number. So the original `x` becomes `x*(n+1)`, while the difference is `n*x`.

If you want to say that the latter number is just `n` times the former, then it is "增加了(原来的)n倍"

However, in casual speech, people may not always respect this rule, which makes it confusing. Sometimes we have to make a confirmation to make sure we get the real number.

They both express doubled.

It’s a bit like how:

• a 100% increase (一倍)

is the same as

• a two-fold increase (两倍)

A phenomenon that is equally confusing in English.

Compare: 一倍 example sentences from ABC

and 两倍 example sentences from Tuttle

• Are you aware of the difference between 扩展/增加n倍 and X是Y的n倍？
– dan
May 26 '18 at 23:40
• @dan Of course. Unless I misunderstood the question I believe that OP's issue is how 一倍 and 两倍 can mean the same thing. So I decided to use this angle to show how they both mean double.
– Mou某
May 28 '18 at 7:32

Math:

So, 我的分数是你的一倍 imply scores are equal technically.

The right one should be 我的分数比你多一倍.

1. X 比 Y 增加n倍: X = Y*(n+1);

2. X 是 Y 的n倍: X = Y*n;

3. X 比 Y 多n倍: X = Y*(n+1);

Those phrases are clear and will not cause any confusion.

In fact, the most confusing phrase is X 比 Y翻n倍. Some take it as X = Yn, some think X = Y(n+1), and some even think X = Y* 2^n. I indeed don't have any official answer for this so far.