If you are going to compare countries with a billion inhabitants, like China, with ones that have 340 million, like the US, and with those that have only 50 mil

If you are going to compare countries with a billion inhabitants, like China, with ones that have 340 million, like the US, and with those that have only 50 million, say South Korea, you surely need to normalise the figures. Otherwise it's not really an apples to apples comparison. Perhaps population ratio isn't the right choice, any suggestions for another?