Hi, Tim! Welcome to "Gotmead?"!!
If you poke around the site a bit more you'll find that most of the recipes are submitted from folks in the US, and so any recipe not citing a difference is assumed to be measured in US gallons.
If you read a bit more (including the Newbee Guide - a link can be found on the left side of this page), you'll find that volumetric quantities are "guidelines" only, since the best and most consistent way to mix any recipe is to reference a starting specific gravity (or alternately, a sugar content measured in the winemaking standard, degrees brix). Working to a known starting gravity, with other ingredients measured by weight rather than volume, is the best way to go when honey (and other ingredients) from different sources can vary (sometimes significantly) in net sugar content.
