Stoneware is a vitreous or semi-vitreous ceramic ware made primarily from non-refractory fire clay.

One widely-recognized definition is from the Combined Nomenclature of the European Communities, a European industry standard. It states:

"Stoneware, which, though dense, impermeable and hard enough to resist scratching by a steel point, differs from porcelain because it is more opaque, and normally only partially vitrified. It may be vitreous or semi-vitreous. It is usually coloured grey or brownish because of impurities in the clay used for its manufacture, and is normally glazed."

Formulations for stoneware vary considerably, although the vast majority will conform to: plastic fire clays 0–100%, ball clays 0–15%, quartz 0–30% feldspar and chamotte 0 –15%

Stoneware is generally once-fired. Maximum firing temperatures can vary significantly, from 1100 °C to 1300 °C depending on the flux content. Typically temperatures will be between 1180°C to 1280°C, the higher end of which equate to Bullers Rings 38 to 40 & Seger cones 4 to 8. To produce a better quality fired glaze finish twice firing can be used, and this can be especially important for formulations composed of highly carbonaceous clays. For these, biscuit firing is around 900 °C and glost firing 1180–1280 °C. Water absorption of stoneware products is less than 1%.