“How big is a sheet of plywood” is a common question we get asked, and it depends whether you mean plywood sheet thickness in mm or the dimensions in either metric or imperial. The standard dimensions are 2440mm x 1220mm or 8” x 4” respectively whereas plywood sheet thickness can vary.Thin plywood sheets start at 5.5mm and large plywood sheets go all the way up to 25mm, depending on your requirements. We have a wide variety of different thicknesses to suit the type of job you need to do. It should be noted that Marine plywood, while thinner than our other plywood, actually has more density to it, so while the sheets can be thinner, they are actually more durable than a hardwood plywood sheet of the same thickness.