 https://www.eia.gov/tools/faqs/faq.cfm?id=667&t=6

How much coal, natural gas, or petroleum is used to generate a kilowatthour of electricity?

The amount of fuel used to generate electricity depends on the efficiency or heat rate of the generator (or power plant) and the heat content of the fuel. Power plant efficiencies (heat rates) vary by types of generators, power plant emission controls, and other factors. Fuel heat contents also vary.

Two formulas that can be used to calculate the amount of fuel used to generate a kilowatthour (kWh) of electricity:
• Amount of fuel used per kWh = Heat rate (in Btu per kWh) / Fuel heat content (in Btu per physical unit)
• Kilowatthour generated per unit of fuel used = Fuel heat content (in Btu per physical unit) / Heat rate (in Btu per kWh)

Calculation examples using these two formulas and the assumptions below:
• Amount of fuel used to generate 1 kilowatthour (kWh): • Coal = 0.00052 short tons or 1.05 pounds
• Natural gas = 0.01010 Mcf (an Mcf equals 1,000 cubic feet)
• Petroleum = 0.00175 barrels (or 0.07 gallons)

• Kilowatthour generated per unit of fuel used: • 1,904 kWh per ton, 0.95 kWh per pound, of coal
• 99 kWh per Mcf (1,000 cubic feet) of natural gas
• 570 kWh per barrel, or 13.6 kWh per gallon, of petroleum
Assumptions:
Power plant heat rate1

Coal = 10,089 Btu/kWh
Natural gas = 10,354 Btu/kWh
Petroleum = 10,334 Btu/kWh

Fuel heat contents2

Coal = 19,210,000 Btu per short ton (2,000 pounds) Note: heat contents of coal vary widely by types of coal
Natural gas = 1,025,000 Btu per 1,000 cubic feet (Mcf)
Petroleum = 5,892,000 Btu per Barrel (42 gallons) Note: Heat contents vary by type of petroleum product

1 Heat rates for steam electric generators in 2013.
2 Heat contents for fuels consumed by the electric power sector in 2013.