Floorspace estimates may be converted to metric units by using the relationship, 1 square foot is approximately equal to .0929 squaremeters. Energy estimates may be converted to metric units by using the relationship, 1 Btu is approximately equal to 1,055 joules. One kilowatthour is exactly 3,600,000 joules. One gigajoule is approximately278 kilowatthours (kWh).