Minimill, traditionally, is a secondary steel manufacturer; it usually gains the majority of iron from scrap steel, recycles used equipment or byproducts of manufacturing. Typical mini-mill melts scrap with electric arc furnace, controls chemistry with ladle furnace or vacuum furnace, converts molten steel to solid form by strip or billet continuous caster.

Originally, mini mill was only applied to production of bar products, like concrete reinforcing bar, flats, angles, channels, pipe, and light rails. Until the late 1980s, the introduction of the direct strip casting process made mini mill production of strip possible. Mini rolling mill usually locate in an area without other steel production, taking advantage of local markets, resources, and lower-cost labor. Mini mill plants may specialize, for instance, in making coils of rod for wire-drawing,

or pipe, or in special function of transportation, agriculture, industry and etc.

Capacities of mini rolling mill vary in different size. Some big plants may produce as much as 3,000,000 tons per year, the typical size is usually in the range of 200,000 to 400,000 tons per year, but some old or small plants may manufacture as little as 50,000 tons per year of finished product. For example, Nucor Corporation, produces about 9,100,000 tons of sheet steel, 6,700,000 tons of bar steel and 2,100,000 tons of plate steel every year.

Since that electric arc furnace can be started and stopped regularly, mini rolling mills can satisfy the market demand easily. When demand is high, it can be operated on 24-hour schedules and cut down production if sales are lower.