As the title shows, "3 times bigger than" =3 times as big as or 4 times as big as. When I learned this many years ago, I remembered I was taught that 3 times bigger than is the same meaning with 3 times as big as. In the grammar books I read, all agrees that 3 times bigger than means 4 times as big as. say, "China's population is 4 times larger than that of the U.S." is totally different with "China's population is 4 times as large as that of the U.S."
I totally went nuts when I read about a completely different understanding that 3 times bigger than actually means 3 times as big as in another grammar book recently.
Which one is currently used among native speakers??
So, you can never be sure when you read this in newspapers, etc. and it's best not to use it if you want to be understood. It can always be replaced with "4 (or 3) times as big".