Gas units
Introduction
This article shows ho to convert between the various ways of measure natural gas volume and energy content.
Typically gas meters record usage in cubic metres or hundreds of cubic feet (and its worth checking yours matches the units your gas supplier is billing you in!)
Basic data
The energy density of natural gas is typically in the range of 37.5 to 43 MJ/m³
1 kW equates to 3.6MJ / hour
(Note there is some variability in this relationship, as the energy content of the gas itself will vary slightly depending on its composition - suppliers will often include a "fiddle factor" on their bills to tune out the variance)
Converting
Use the following conversion factors to work out what you need from what information you have:
| Task | Conversion factor |
|---|---|
| 100 CU feet (1 unit) to cubic metres | Multiply by 2.83 |
| 100 CU feet (1 unit) to kWh | Multiply by 32.15 |
| Cubic metres to 100s cubic feet | Divide by 2.83 |
| Convert from m³ to kWh | Multiply by 11.36 |
| Convert from a rate of consumption in kW, to cubic metres per hour | Multiply by 0.09 (approx) |
| Convert 1000 BTU/h into kWh | Multiply by 0.293 |
Examples
Conversion from units to kWh
You have used 40 units on your imperial gas meter. What is that in kWh?
Convert 100s of cubic feet to m³: 40 x 2.83 = 113.2m³
So in kWh = 113.2 x 11.36 = 1,286 kWh
Work out the gas rate required by your new boiler
Your new boiler can demand a maximum input power of 24kW. How much is that in cubic meters of gas per hour?
24 x 0.09 = 2.16 m³
(Note that if the boiler specification states the output power rather than the input power, you will likely need to add 10% to 20% to the power stated before conversion to arrive at the actual gas rate. This allows for inefficiency in the boiler, since not all the energy delivered in the gas is converted to usable heat by the boiler)
Once you know the amount of gas required in m³ / hour, you can then check if you will need to upgrade your gas pipework to cope with the boiler.
How powerful is my 80,000 BTU/h boiler in kW?
80,000 / 1000 x 0.293 = 23.44 kW