Gas Units to kWh Converter

About the Gas Units to kWh Converter

Gas meters measure volume — cubic metres, hundreds of cubic feet or standard cubic metres — but gas is charged for its energy, in kWh, therms or MMBtu. Converting needs a figure from the bill: the calorific value, the energy in each cubic metre, and in the UK the volume correction factor too. Great Britain’s rule is set in law: kWh = cubic metres × 1.02264 × calorific value (MJ/m³) ÷ 3.6, and an imperial meter’s units (hundreds of cubic feet) are first multiplied by 2.83.

Choose your gas: a UK meter in m³ or ft³, India PNG in SCM with the GCV in kcal/SCM, a US bill in CCF and therms, LPG by kg, litres or cylinder (14.2, 5 and 19 kg, or 20 lb), another meter with its own correction factor and calorific value, or plain energy units. Type the units used or two meter readings, and the converter gives kWh, MJ, therms, MMBtu and kcal with every step of the working. It converts units only: your tariff sets the price.

Common uses

• Checking the kWh on a UK gas bill from the meter readings.
• Working out the units of an imperial (cubic feet) meter in kWh.
• Comparing PNG in SCM with LPG cylinders, or with electricity in kWh.
• Converting an industrial gas quantity between SCM and MMBtu.
• Reading a US bill in CCF and therms as kWh.

The UK formula

The Gas (Calculation of Thermal Energy) Regulations 1996 set how gas is turned into kWh in Great Britain:

• the volume registered by a meter that is expected to pass no more than 732,000 kWh a year is multiplied by the temperature and pressure conversion factor 1.02264, which gives its volume at 15 °C and 1013.25 mbar;
• a volume registered in cubic feet is multiplied by 0.0283 first, so one unit of an imperial meter (100 ft³) is 2.83 m³;
• kWh = converted volume (m³) × calorific value (MJ/m³) ÷ 3.6, the calorific value being the average for the billing period, with anything under 0.1 MJ/m³ ignored.

Your bill prints the calorific value. The Digest of UK Energy Statistics puts the average gross calorific value of the gas consumed in the UK at about 39.3–39.7 MJ/m³, which is why the converter starts at 39.5. Larger sites use measured temperature, pressure and compressibility factors instead of 1.02264: type their factor in the correction box.

India: SCM, GCV and MMBtu

Piped natural gas is billed by the standard cubic metre (SCM): one cubic metre at 1 atmosphere and 15.56 °C. Its energy is its gross calorific value (GCV) in kcal per SCM; PPAC (Ministry of Petroleum and Natural Gas) converts at 10,000 kcal/SCM, so 1 MMBtu = 25.2 SCM, and it gives the gas produced in India as 8,000–9,480 kcal/SCM on average — use the GCV on your bill when it is printed. The kcal here is the International Table kilocalorie (4.1868 kJ): 1 kWh = 859.85 kcal and 1 MMBtu = 251,996 kcal, which PPAC rounds to 252,000.

US: CCF, therms and MMBtu

US meters read in CCF (hundred cubic feet) or MCF (thousand cubic feet). A bill that charges in therms converts the volume with a therm factor, the therms in each CCF of the gas delivered: therms = CCF × therm factor. A therm is 100,000 Btu; the FTC’s EnergyGuide cost tables take a cubic foot of natural gas as 1,039 Btu, which is 1.039 therms per CCF and the converter’s starting value. NIST gives the US therm as 105.4804 MJ (29.3001 kWh), the legal unit of the US gas industry, and the EC therm as 105.506 MJ (29.3072 kWh); an MMBtu is a million International Table Btu, 293.07 kWh.

LPG: kg, litres and kWh

LPG is sold by weight (cylinders) or by the litre of liquid (tanks). The converter works from the NIST Chemistry WebBook: propane gives 50.33 MJ/kg gross (46.34 net) and n-butane 49.51 MJ/kg gross (45.72 net), and the liquids weigh 0.5075 and 0.5843 kg per litre at 15 °C. PPAC gives LPG in India as 40% propane and 60% butane, the converter’s mix for India (taken by mass): 49.84 MJ/kg and 0.551 kg/L, so a 14.2 kg cylinder holds about 196.6 kWh (gross) in 25.8 L of liquid. IS 4576, India’s LPG standard, covers commercial butane, butane–propane mixtures and propane; it limits the vapour pressure and the composition but sets no density or calorific value, which is why both boxes can be edited. As a check, the FTC takes a US gallon of propane as 91,333 Btu; the NIST figures give about 91,600 Btu for pure propane at 15 °C.

Gross and net calorific value

The gross (higher) calorific value includes the heat given back when the water vapour in the flue gases condenses; the net (lower) value leaves it out. The UK averages above are gross values (DUKES puts the net value of the same gas at about 35.5 MJ/m³), and India’s GCV is gross by name. PPAC takes the net value of natural gas as 90% of the gross; for LPG the NIST figures above give about 92%. Choose Net under LPG when a boiler or engine efficiency is quoted on the net basis.

Sources

• The Gas (Calculation of Thermal Energy) Regulations 1996 (SI 1996/439), regulations 2 and 3
• DUKES: calorific values and density of fuels, Table A.1
• NIST SP 811, Appendix B.9 — calorie, kWh, therm (EC) and therm (U.S.)
• PPAC Ready Reckoner, Tables 9.1, 9.4 and 9.5 (natural gas conversions)
• 16 CFR Part 305, Appendix K1 — therm and Btu per cubic foot in the FTC’s cost tables
• NIST Chemistry WebBook — heats of combustion and liquid densities of propane and n-butane

Limitations

• This converts quantities only. It does not know your tariff, standing charge or taxes.
• Use the calorific value, GCV or therm factor printed on your bill: the starting values are typical, and the gas delivered varies from place to place and day to day.
• The UK regulations ignore any part of the average calorific value under 0.1 MJ/m³ and a bill may round the kWh, so it can differ from the converter by a fraction of a unit.
• LPG figures are worked out for propane and n-butane. Commercial LPG also contains propylene, butylenes and isobutane, so its density and calorific value differ a little: use your supplier’s figures when you have them.
• Liquid LPG volumes are at 15 °C; the liquid expands as it warms.

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