The energy of various amounts of the explosive TNT (kiloton, megaton, gigaton) is often used as a unit of explosion energy, and sometimes of asteroid impacts and violent explosive volcanic eruptions. One ton of TNT produces 4.184 × 10 joules, or (by arbitrary definition) exactly 10 thermochemical calories (approximately 3.964 × 10 BTU). This definition is only loosely based on the actual physical properties of TNT.