Dragonmark size

[Kish]

I can't find anywhere in the Eberron books that specifies how large an area of skin an average dragonmark of each type (least, lesser, greater, Siberys, aberrent) takes up.

Is it in a book somewhere, or did they just handwave it?

[Red Fel]

I can't find anywhere in the Eberron books that specifies how large an area of skin an average dragonmark of each type (least, lesser, greater, Siberys, aberrent) takes up.

Is it in a book somewhere, or did they just handwave it?

Well, the Eberron Wiki offers an answer (http://eberron.wikia.com/wiki/Dragonmarks):

There are three distinct manifestations of each dragonmark that correlate in size, intricacy and power. As the dragonmark gains power (from least to greater) it will expand in size and complexity rather than forming a different mark.

Much rarer are the so called Heirs of Siberys who possess the Siberys Mark, marks that cover much, if not all, of their body.
However, that's just a wiki, not an official source. There is, however, the following passage on page 7 of Dragonmarked:
Nearly all dragonmarked heirs first manifest the least mark of their house. When a character increases her dragonmark's power, the mark physically expands. A typical least dragonmark covers an area 2 inches square on the skin. Lesser marks are typically 3-5 inches across, while greater dragonmarks are 6-8 inches. Siberys dragonmarks are vast designs that often cover the bearer's entire chest or torso.

[Kish]

Thanks, that's what I was looking for.

[Red Fel]

Thanks, that's what I was looking for.

If your DM is amenable, I'd just fluff it. I have one character with a Mark of Storms that I describe as starting on the back of the hand (least), then growing around the forearm like a bracer (lesser), then finally crawling up the arm and edging onto the chest (greater). It's a purely aesthetic choice, I just think it's wicked awesome.

To my knowledge, that passage in Dragonmarked is the only RAW statement of dimensions, so your DM might be agreeable if you decide to fudge a bit.

[Godskook]

The smallest dragonmarks(mostly least) might be little enough to fight on the back of someone's hand, and the biggest Syberis mark would like cover every patch of skin. For some idea, the ECS provides pictures alongside two prestige classes that give some good range(Heir of Syberis and Dragonmarked Heir).

[Kish]

I appreciate the thought, but

A typical least dragonmark covers an area 2 inches square on the skin. Lesser marks are typically 3-5 inches across, while greater dragonmarks are 6-8 inches.
is what I was looking for, and I have no need to argue with it.