Y'know... I was wondering. Harbinger was the first of the Reapers and is noticibly larger than Sovereign. I was wondering if Reapers, despite having mostly-synthetic bodies, still grow like an organic life-form as they get older?
I only really need the size numbers to come up with something beleivable in terms of weapons. However, I think the Asari ship designs are absurd, there is no barrel for a main gun! Unless of course we are talking about death by a thousand papercuts i.e. the Ascension actually mounts like 50 heavy cruiser class mass accelerators.
It would be nice if you could post the size charts
Unfortunately BioWare didn't grace us with a chart. However we can work one out easily. First of all. There are 4 kinds of Reapers, but we only see two, the small Destroyers, which are 160 meters in length and the large Sovereign-class monsters, those are 2 kilometers long, Harbinger is said to be the oldest and largest Reaper so, I'd bet that he's probably around 2.3 - 2.4 - 2.5 kilometers long.
The Alliance Navy has quite a few types of ships, two dreadnought classes, a carrier, a cruiser and a frigate class, plus fighters. There's the older and larger Everest-class 888 meters in length, that can be seen above under the cruiser, there's also the newer Kilimanjaro-class which is armed with 156 broadside mass accelerator cannons, 78 on each side. The broadside guns are each as long as 40% of the ship's width. But the Kilimanjaro are only mentioned in the Codex. I did some calculations and the Alliance Cruiser, compared to the Everest is roughly 500-550 meters long. There are two types of Cruisers so far that we know of, one class is yet unnamed and the Geneva-class, now, as to which one is portrayed in ME3, I guess we'll never know. As for frigates, you got your Normandy-class, there are two of them, the SSV Normandy and the SSV Ain Jalut, and then there's the SR-2 from ME2, and an unknown class which makes up the bulk of the frigate forces in the Alliance. Carriers are an oddball as only the Alliance has them, class name yet unknown, however, there's only 3, they're also said to be roughly Alliance dreadnought sized.
The Turians, yet another BioWare carelessness, their Cruisers and Frigates apparently look identical, the only difference is of course, size, armor, speed, maneuverability and firepower. They also have fighters, probably carried in small numbers. The Volus were given a dreadnought, by the Turians, the Kwunu as a gift, it also looks exactly like all the other Turian vessels, just probably a shitload larger. A Turian cruiser is a bit shorter than an Alliance cruiser, somewhere between 480-530 meters perhaps, there's a cinematic at the end of ME3, if you don't gather enough forces a Reaper destroyer piggybacks a Turian cruiser, so that's good size reference as well.
The Asari, well, only seen two ships of theirs, dreadnoughts and cruisers. You can easily tell them apart in the final battle.
The Quarian cruiser that's also in the pic I posted is more than likely around the same size as a Turian or Alliance cruiser, extrapolating from that, an Alliance Everest-class dreadnought is a bit shorter than a Quarian Live ship's tail section.