The below lists the main Port bottle sizes. The most common sizes are the half bottle, standard bottle and magnum, with larger sizes being rarer.
37.5cl Half: Equivalent to one-half of the standard 75cl bottle.
"...the perfect size for two or three people wishing to enjoy a freshly decanted Vintage Port..." Adrian Bridge, Fladgate Partnership
75cl Standard: Most common bottle size.
150cl Magnum: Equivalent to two standard 75cl bottles.
225cl Tappet-Hen: Equivalent to thee 75cl bottles.
"If you appreciate large format bottles of Port wine there are few sizes that are more captivating than Tappit-hen bottlings." Roy Hersh, For The Love of Port
300cl Double Magnum: Equivalent to four standard 75cl bottles or two 150cl Magnums.
600cl Imperial: Equivalent to eight standard 75cl bottles or two 300cl Double Magnums.These majestic bottles are rare and much prized by collectors
"...impressive and memorable way of serving Vintage Port to a large number of guests." Adrian Bridge, Fladgate Partnership