How big is one acre of land?

Of course in NZ/Aus we also have the "long acre" - which is the bit of road frontage beside your official acreage that you can sometimes make use of !

Marcy, One hectare is 10 000 m2. So an acre is about 0.4 Hectares. Or 2.5 acres to a Hectare.

is an acre 40% of 1000 sq.meter??

Not used in Oz or NZ anymore but we still talk in acres! "how many acres do you have here?" We use centimetres/metres too but talk about our height "my eldest son is 6'6" six foot six inches" (which is true!).