A variable cost is a constant amount per unit produced or used. Therefore, the total amount of the variable cost will change proportionately with volume or activity. Generally, a product's direct materials are a variable cost. To illustrate, let's assume that a bakery uses one pound of flour at a cost of $0.70 per pound for every loaf of bread it produces.
Most sports fields are one hectare in size. The Apple Bowl in Kelowna for instance is a 400 m running track and the grassy area inside is 1.12 hectares. The international rugby field pictured above is very close to one hectare in size, it is actually 1.0008 hectares. A perfect square is 100 meters by 100 meters is a hectare. An acre is about 0.4047 hectare and one hectare contains about 2.47 acres.
Most people just know that an acre is a big piece of land, and that 6 acres are more than 5 acres. As a unit of measurement it is hopeless. By contrast, as described in previous comments, 100 m X 100 m = 10 000 square metres (m2) = a hectare (ha), and 100 ha = a square kilometre (km2). Dead easy. The size of a football pitch has not changed significantly for over a hundred years.