Britannis was the largest of the three, It was wider, and heavier as a ship was deemed bigger if it was heavier than an other, thats why titainic was bigger than olympic only because of its larger weight. Britannic was heavier and wider so yeah it was the biggest. Popular belief says britannic measured 903 feet over titabnic and olympics 882, but the plans argue it was the exact same. So all three measure 882feet (and five inches i think, am certain its 882 feet not sure of the inches) or 269 metres.