I know this is a dumb question but what can you get for a mile? Like how many miles do you need to say travel to Japan? Does it differ between airlines?

Different companies set their miles reward differently.

I think Aaron said it the best when he said miles are like different currencies, like USD vs SGD.

Another point to note is that different mile programs have different partners. For example Krisflyer has a lot more working credit card partners than Asia Miles, so it is much easier to find a credit card that has krisflyer points than one for Asia Miles.​​​

I believe most of the responses here would have shown that the miles differ across airlines. As a reference, here are the three examples on these airlines for your comparison:

JAL: https://www.jal.co.jp/en/jmb/award_renewal/rout...

ANA: https://www.ana.co.jp/en/sg/amc/reference/tamer...

SQ: https://www.singaporeair.com/en_UK/ppsclub-kris...

Different airlines have different miles requirement to go to a certain country, just like how different airlines have different price points to the same country. For a start, you can take reference from Krisflyer miles to Tokyo which is 94,000 miles for business class. From the SQ website, there is also a miles calculator where you can see how much miles you need to go to a specific country.

For Japan you will need at least 54k miles to redeem an return economy on SIA. Do take note miles needed keeps increasing over time like inflation so next time it won't be 54k miles.

The redemption of airmiles amount also differs across diferent airlines​​​