The Collaborative International Dictionary of English v.0.48:

Acreage \A"cre*age\, n.
   Acres collectively; as, the acreage of a farm or a country.
   [1913 Webster]

WordNet (r) 3.0 (2006):

acreage
    n 1: an area of ground used for some particular purpose (such as
         building or farming); "he wanted some acreage to build on"
         [syn: acreage, land area]

Moby Thesaurus II by Grady Ward, 1.0:

27 Moby Thesaurus words for "acreage":
   area, breadth, continuum, dimension, emptiness, empty space,
   expanse, expansion, extension, extent, field, galactic space,
   infinite space, interstellar space, measure, nothingness,
   outer space, proportion, space, spatial extension, sphere, spread,
   superficial extension, surface, tract, void, volume