http://bioenergy.ornl.gov/papers/misc/energy_conv.html is the origin of this data...

Energy units

• 1.0 joule (J) = one Newton applied over a distance of one meter (= 1 kg m²/s²).
• 1.0 joule = 0.239 calories (cal)
• 1.0 calorie = 4.187 J
• 1.0 gigajoule (GJ) = 10⁹ joules = 0.948 million Btu = 239 million calories = 278 kWh
• 1.0 British thermal unit (Btu) = 1055 joules (1.055 kJ)
• 1.0 Quad = One quadrillion Btu (10¹⁵ Btu) = 1.055 exajoules (EJ), or approximately 172 million barrels of oil equivalent (boe)
• 1000 Btu/lb = 2.33 gigajoules per tonne (GJ/t)
• 1000 Btu/US gallon = 0.279 megajoules per liter (MJ/l)

• 1.0 watt = 1.0 joule/second = 3.413 Btu/hr
• 1.0 kilowatt (kW) = 3413 Btu/hr = 1.341 horsepower
• 1.0 kilowatt-hour (kWh) = 3.6 MJ = 3413 Btu
• 1.0 horsepower (hp) = 550 foot-pounds per second = 2545 Btu per hour = 745.7 watts = 0.746 kW

• $1.00 per million Btu = $0.948/GJ
• $1.00/GJ = $1.055 per million Btu

Some common units of measure

• 1.0 U.S. ton (short ton) = 2000 pounds
• 1.0 imperial ton (long ton or shipping ton) = 2240 pounds
• 1.0 metric tonne (tonne) = 1000 kilograms = 2205 pounds
• 1.0 US gallon = 3.79 liter = 0.833 Imperial gallon
• 1.0 imperial gallon = 4.55 liter = 1.20 US gallon
• 1.0 liter = 0.264 US gallon = 0.220 imperial gallon
• 1.0 US bushel = 0.0352 m³ = 0.97 UK bushel = 56 lb, 25 kg (corn or sorghum) = 60 lb, 27 kg (wheat or soybeans) = 40 lb, 18 kg (barley)

Areas and crop yields

• 1.0 hectare = 10,000 m² (an area 100 m x 100 m, or 328 x 328 ft) = 2.47 acres
• 1.0 km² = 100 hectares = 247 acres
• 1.0 acre = 0.405 hectares
• 1.0 US ton/acre = 2.24 t/ha
• 1 metric tonne/hectare = 0.446 ton/acre
• 100 g/m² = 1.0 tonne/hectare = 892 lb/acre
  • for example, a "target" bioenergy crop yield might be: 5.0 US tons/acre (10,000 lb/acre) = 11.2 tonnes/hectare (1120 g/m²)

Biomass energy

• Cord: a stack of wood comprising 128 cubic feet (3.62 m³); standard dimensions are 4 x 4 x 8 feet, including air space and bark. One cord contains approx. 1.2 U.S. tons (oven-dry) = 2400 pounds = 1089 kg
  • 1.0 metric tonne wood = 1.4 cubic meters (solid wood, not stacked)
  • Energy content of wood fuel (HHV, bone dry) = 18-22 GJ/t (7,600-9,600 Btu/lb)
  • Energy content of wood fuel (air dry, 20% moisture) = about 15 GJ/t (6,400 Btu/lb)
• Energy content of agricultural residues (range due to moisture content) = 10-17 GJ/t (4,300-7,300 Btu/lb)
• Metric tonne charcoal = 30 GJ (= 12,800 Btu/lb) (but usually derived from 6-12 t air-dry wood, i.e. 90-180 GJ original energy content)
• Metric tonne ethanol = 7.94 petroleum barrels = 1262 liters
  • ethanol energy content (LHV) = 11,500 Btu/lb = 75,700 Btu/gallon = 26.7 GJ/t = 21.1 MJ/liter. HHV for ethanol = 84,000 Btu/gallon = 89 MJ/gallon = 23.4 MJ/liter
  • ethanol density (average) = 0.79 g/ml ( = metric tonnes/m³)
• Metric tonne biodiesel = 37.8 GJ (33.3 - 35.7 MJ/liter)
  • biodiesel density (average) = 0.88 g/ml ( = metric tonnes/m³)

Fossil fuels

• Barrel of oil equivalent (boe) = approx. 6.1 GJ (5.8 million Btu), equivalent to 1,700 kWh. "Petroleum barrel" is a liquid measure equal to 42 U.S. gallons (35 Imperial gallons or 159 liters); about 7.2 barrels oil are equivalent to one tonne of oil (metric) = 42-45 GJ.
• Gasoline: US gallon = 115,000 Btu = 121 MJ = 32 MJ/liter (LHV). HHV = 125,000 Btu/gallon = 132 MJ/gallon = 35 MJ/liter
  • Metric tonne gasoline = 8.53 barrels = 1356 liter = 43.5 GJ/t (LHV); 47.3 GJ/t (HHV)
  • gasoline density (average) = 0.73 g/ml ( = metric tonnes/m³)
• Petro-diesel = 130,500 Btu/gallon (36.4 MJ/liter or 42.8 GJ/t)
  • petro-diesel density (average) = 0.84 g/ml ( = metric tonnes/m³)
• Note that the energy content (heating value) of petroleum products per unit mass is fairly constant, but their density differs significantly – hence the energy content of a liter, gallon, etc. varies between gasoline, diesel, kerosene.
• Metric tonne coal = 27-30 GJ (bituminous/anthracite); 15-19 GJ (lignite/sub-bituminous) (the above ranges are equivalent to 11,500-13,000 Btu/lb and 6,500-8,200 Btu/lb).
  • Note that the energy content (heating value) per unit mass varies greatly between different "ranks" of coal. "Typical" coal (rank not specified) usually means bituminous coal, the most common fuel for power plants (27 GJ/t).
• Natural gas: HHV = 1027 Btu/ft3 = 38.3 MJ/m³; LHV = 930 Btu/ft3 = 34.6 MJ/m³
  • Therm (used for natural gas, methane) = 100,000 Btu (= 105.5 MJ)

Carbon content of fossil fuels and bioenergy feedstocks

• coal (average) = 25.4 metric tonnes carbon per terajoule (TJ)
  • 1.0 metric tonne coal = 746 kg carbon
• oil (average) = 19.9 metric tonnes carbon / TJ
• 1.0 US gallon gasoline (0.833 Imperial gallon, 3.79 liter) = 2.42 kg carbon
• 1.0 US gallon diesel/fuel oil (0.833 Imperial gallon, 3.79 liter) = 2.77 kg carbon
• natural gas (methane) = 14.4 metric tonnes carbon / TJ
• 1.0 cubic meter natural gas (methane) = 0.49 kg carbon
• carbon content of bioenergy feedstocks: approx. 50% for woody crops or wood waste; approx. 45% for graminaceous (grass) crops or agricultural residues