How big is Eberron?

EBERRON

Radius - 2,963 miles
Diameter - 5,926 miles
Circumference - 18,617 miles
Surface Area - 110,324,805 mi²

Aerenal - 1,025,000 mi²
Argonnessen - 5,140,000 mi²
Everice - 2,378,000 mi²
Islands - 670,000 mi²
Khorvaire - 6,975,000 mi²
Sarlona - 7,520,000 mi²
Zendikar - 12,724,000 mi²

Total land area - 36,432,000 mi²
Percentage - 33%

Total area covered in water - 73,892,800 mi²
Percentage - 67%

Comparatively, the subcontinent of Aerenal is about half the size of Australia, while Argonnessen is slightly smaller than Antarctica. The Everice, south of Zendikar, is of a comparable size with Australia. The islands of Eberron compose about a 3rd again more land area than the islands of earth. Khorvaire is slightly larger than South America and twice the size of the United States. Sarlona is larger than North America, and Zendikar is slightly larger than Africa, about half the size of Eurasia.

Khorvaire's land area is taken from the new 5th edition maps. The other continents were scaled according to personal preference. The precise circumference of Eberron is difficult to parse, but is generally agreed to be somewhere between that of Mars and Earth. I opted for a larger size than previous estimates (16,513 miles) because it gave a more comparable land-to-water ratio.

Oceanic Trade

Using this scale, Eberron can be circumnavigated in a Lyrandar Elemental Galleon sailing at 20 mph in roughly 50 days; a traditional sailing ship would take 6 months, or about half a year. The trip is faster than a comparable journey on earth because of the size of the planet, but also because Eberron's continents do not block the way. Argonnessen and Zendikar are primarily in the southern hemisphere, while Khorvaire and Sarlona are primarily in the northern, leaving the equator open to shipping lanes.

Due to this fact, as well as the size of the metropolis Sharn, I would imagine that trade between the 6 major continents of Khorvaire, as well as numerous smaller islands, is actually quite robust, similar to the spice road of the medieval period. The major ports of call would be Sharn, travelling along the southern coast of Khorvaire through Zolanport and Korranberg, before crossing the Kraken bay and making port in Pylas Maradal, in Valenar. Before the Mourning, Seaside in Cyre was an important stop, and Darguun has tried making Wyvernskull more attractive to sea trade as well. Another likely port, heading south from Korranberg, is Pylas Talaear in Aerenal. Crossing the Dragonreach sea, Seren likely has a large city for trading as well, though it is not mentioned in any source materials that I have found. From there, ships cross the Sea of Rage to Dar Ulatesh, the largest and most important port city of Riedra, before heading south to Syrkarn and rounding the treacherous horn of Adar, with few if any hospitable ports. From Adar is the long stretch of the Barren Sea, comparable to the Pacific, filled with small islands, before finally reaching the Kapaerian Island, or perhaps being waylaid by a storm and being driven south into the Sea of Lost Souls, to Dar Qat in Menechtarun. From there, the coast leads to Stormreach, and then across the Straights of Shargon back to Sharn.