It wasn't so big physically, then I moved to Japan and started to work.
Lots of money + cheap manga = exponential growth of my collection.
Now I have about 8 series in English, and about 20 in Japanese. It totals about 100 volumes (which is still pretty small I'll grant).

Digitally, I have hundreds and hundreds of volumes worth of manga. I've never counted, but it takes up about 250GB.

This is nothing compared to my novel collection, but then again it had a head start.

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The pen is mightier than the sword...and considerably easier to write with.

464 volumes as of my last Amazon shipment. Most of the stuff I already own are either completed, on hiatus (by the manga-ka), or cancelled by the American publishers (tough times). Currently completing four ongoing series which will run or are running past the 10-volume mark.

I don't buy any manga, I read online

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朝露の少女。

“The longer we live, the more weight we carry in our hearts.”

Thats what I will call a politically stupid answer. I am sure you know why people buy manga's even though you can read them online,dont you?

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I have a small collection of manga series. I try my best not buying any long running series or on-going series. Manga's I have bought are:
-Pluto
-MBQ
-Peepo Choo
-Lupin III
-Street Fighter 2
-Street Fighter Alpha
-Street Fighter: Ryu Final
-Dragon Ball (Volume 5 to 9 and 36 to 42)
-Ayako
-Gunsmith Cats
-Shadows of Spawn
-Afro Samurai
-SandLand
-Parasyte
-Gantz ( volumes 1 to 3)
-Slam Dunk (Volumes 1 to 6)

I am planing to sell some of my manga series though. I'm trying my best only buying mangas I'm going to re-read over and over again.

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Just kidding!
I do buy real life copies. But online reading is still my main activity since they don't sell series I like in my country. But when they do, I would buy them to support the mangaka even if i have read the manga
On my self there are about 200 volumes and still increasing every time I see my targets.

I don't buy too much manga (irl), maybe about ten volumes a year. However, my external hard drive is chock full of manga

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Being alone is only lonely if you want it to be.
Staying in lucid delusion for an eternity.

I only have about 50 manga, I would buy a lot, but they are expensive. I would like to find more sales and deals. The best deal I've found was four volumes of Loveless for $10.00.

all in all, I read online for series not in English, and series I like I will buy when they are translated.

I kinda stopped counting somewhere after 600 volumes. I don't buy as much as I used to.
Mangas of the digital kind, hmm, I have them on various harddrives. About 500GB if I had to guess, and growing daily.

5gb yehhhh!
[m]

I think I have about 20+ volumes. I only started collecting manga earlier this year, and currently, my main focus is to buy the next volumes of my favorite series once they are released, especially those whose scanlators stopped (such as Afterschool Charisma).

Just like most of you, I also have a huge number of manga stored in my external hard drive and in my laptop.

800 now. So glad to hit that mark n_n.
Now just to get to 1000!

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I have purchased every english volume of One Piece, and a few japanese volumes I found in used bookstores (Kohinata Minoru, PokeSpe) in Japan. I read online mostly, I'm currently following 61 not-fully-scanlated series, and have finished at least a hundred series of 20+ volumes each. Once I graduate college and have an actual income, I will probably be like CuthienSilmeriel above and exponentially increase the total amount of physical manga I own.