For comparison, new generating units built since 1978 were required to limit sulfur dioxide to a "lowest achievable emissions rate" of about 0.6 pounds per million British thermal units (0.93 kg/MWh). Coal with 1.25% sulfur and 10,000 British thermal units per pound (6.5 kWh/kg) produces sulfur dioxide emissions of 2.5 pounds per million British thermal units (3.9 kg/MWh), with lower emissions produced by either lower sulfur content or higher Btu content.[8]