How do I convert therms or cubic metres of gas to kWh?

One therm is about 29.3 kWh. One cubic metre of natural gas is about 10.6 to 11.2 kWh depending on calorific value. This tool lets you enter gas directly in kWh or therms and converts therms for you, so use whichever your bill shows.

What emission factors are used?

Natural gas is about 0.183 kgCO2e per kWh and heating oil about 2.52 kgCO2e per litre. Electricity uses your selected grid factor, since it varies hugely by country, from under 50 gCO2/kWh on very clean grids to over 600 on coal-heavy grids.

Why is electricity's footprint so variable?

Gas and oil burn the same wherever you are, so their factors are fixed. Electricity's carbon depends entirely on how it was generated, which differs by country and even by time of day. That is why the grid factor is a separate, adjustable input here.

What reduction action saves the most?

For most homes, cutting gas heating demand through insulation, draught-proofing, and a lower thermostat saves the most, because gas is usually the largest single energy use. Switching to a heat pump on a clean grid and to a renewable electricity tariff are the next biggest levers.

Does this include embodied or food emissions?

No. This calculator covers operational energy only: gas, electricity, and heating oil consumed in the home. Food, travel, goods, and the embodied carbon of the building itself are separate categories not included in this figure.

What is the Home Energy CO2 Calculator?

Enter annual gas (kWh or therms), electricity (kWh), and heating oil consumption along with your grid region to compute household CO2e using current emission factors. Suggests the top reduction actions with their CO2 savings. For households and landlords. It runs free in your browser on Gera Tools, with nothing uploaded.

Home Energy CO2 Calculator

Name: Home Energy CO2 Calculator
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

Household energy is typically the second-largest part of a personal carbon footprint after travel, and most of it hides in heating. This calculator combines your gas, electricity, and heating-oil use with the right emission factors to give a single annual CO2e figure, then ranks the actions that would cut it the most.

How it works

gas CO2e   = gas_kWh × 0.183
elec CO2e  = elec_kWh × (grid gCO2/kWh ÷ 1000)
oil CO2e   = oil_litres × 2.52
total      = gas + elec + oil   (kg CO2e per year)

Gas and oil factors are fixed because the fuel burns identically everywhere; electricity uses the grid factor you choose, which is the single biggest swing in the result.

Reading your energy bills

Your annual energy bills are the best source of figures:

Gas: annual bills in the UK show consumption in kWh. Some older bills show cubic metres or hundreds of cubic feet — your supplier will usually convert for you, or use: 1 cubic metre ≈ 11.2 kWh, 1 therm ≈ 29.3 kWh.
Electricity: shown directly in kWh on virtually all bills.
Heating oil: oil tank top-ups are sold in litres. Add up the litres delivered across the year (invoices or delivery receipts).

If you do not have annual figures, multiply a typical monthly bill quantity by 12, adjusting upward slightly for colder winter months.

Illustrative worked example

Consider a UK household in a semi-detached house with:

12,000 kWh of gas per year
3,500 kWh of electricity per year (UK grid: roughly 200–250 gCO2/kWh depending on year)
No heating oil

For example, using approximate values for illustration only:

gas CO2e   = 12,000 × 0.183 = 2,196 kg CO2e
elec CO2e  = 3,500 × 0.230  =   805 kg CO2e   (illustrative factor)
total      ≈ 3,001 kg CO2e per year

Gas dominates — over 70% of the footprint. This is typical of UK homes with gas central heating, and is why heating efficiency is the highest-leverage lever.

Why the electricity grid factor matters so much

Two homes with identical electricity consumption but on different grids can have very different carbon footprints from that electricity. Grids that rely heavily on gas peaking plants can have carbon intensities several times higher than grids dominated by nuclear, hydro, or wind. This is why the grid factor is a separate user-adjustable input rather than a fixed constant — and why the CO2e from switching to a renewable tariff (or living in a region with a cleaner grid) can be substantial.

Reduction actions ranked

The tool ranks common measures by estimated CO2 saved:

Thermostat reduction of 1°C — roughly 6–8 percent of heating demand; a meaningful saving with no capital cost.
Loft and cavity-wall insulation — typically cuts heating energy by 15–25% depending on the home.
Draught-proofing doors and windows — low-cost, often 5–10% heating saving.
Switch to a renewable electricity tariff — eliminates most or all of the electricity CO2e, depending on the certificate regime.
Heat pump replacement of gas boiler — on a clean grid, a heat pump can cut heating-related CO2e by 60–80% despite using electricity, because it moves heat rather than generating it.

What this calculator does not cover

The figure covers operational home energy only — gas, electricity, and heating oil burned in the home. Not included: food and diet, travel, flights, purchases of goods, water heating from non-fossil fuels, or the embodied carbon of the building and its appliances. These are material parts of a full personal footprint and should be assessed separately.