Yeah I'd say probably 100,000 total around the world, or maybe more when you factor in illegal downloading (hard to count those people, though not really sure if we should). They're not *huge*, but they're getting to the point in Japan where most people have at least heard of them, at least in Tokyo. When I was there in March (can't believe it's been 2 months already!), we had to turn down a couple dinner invitations because of going to the show, and when we told the people who asked us who we were going to see, they said "oh, Scandal!" and kind of laughed. I don't think they were fans but they were just random people who knew who they were.
I'm always kind of shocked when I look at Japanese sales numbers, though. Even really huge acts don't sell a lot of albums compared to popular artists in the US, especially anymore. (CD sales are down in Japan in general, like here.) AKB48's last album sold 866,000 copies according to Oricon, and you *can't* get away from AKB48 in Japan. So for Scandal to be 1/10 as popular as them I think is actually pretty good.
That's why Japanese artists are expected to do so much... you can't just put out an album every couple of years and go on a tour for it and make money. You have to basically release stuff constantly, put on tours constantly, do pinup calendars, TV commercials, clothes modeling, etc.