Advanced options
What The Gas Cost Calculator Works Out
- Energy used: gas meters measure volume but you are billed for energy. Cubic metres x 1.02264 (the volume correction factor for temperature and pressure) x the calorific value on your bill (typically 37.5 to 43 MJ/m3), divided by 3.6, gives kilowatt-hours. A hundred metric units is about 1,100 kWh.
- Imperial meters: older dials read in hundreds of cubic feet, so the units are multiplied by 2.83 to get cubic metres first. Misreading an imperial meter as metric is a classic cause of terrifying estimated bills, since each imperial unit is nearly three times the gas.
- Total cost: kilowatt-hours x unit rate, plus the standing charge for the days in the period. The kWh figure should match the one printed on your bill for the same readings.
- Standing charge: accrues daily regardless of use, around 30p a day under the current cap, which is why a home using no gas in summer still pays several pounds a month. Editable in advanced options for fixed deals with a different daily charge.
- Cost per day and projected annual cost (advanced): the period total divided by its days, then scaled to 365 days, with annual kilowatt-hours compared with Ofgem's typical household figure of 11,500 kWh. Winter periods will project high and summer periods low.
- Alternative tariff (advanced): the same gas priced at another deal's unit rate and standing charge, with the saving or extra cost for the period and annualised. Low-use homes should weigh a cheaper standing charge more heavily than a cheaper unit rate.
- Change on previous period (advanced): the percentage change in kilowatt-hours against the units used last time, converted at the same calorific value, so you can see whether a bill rise is more gas or a higher price.
- Direct Debit versus cost (advanced): your monthly payment scaled to the period length, less the actual cost, showing whether the account is building credit or running behind. Suppliers aim for a small credit going into winter.
- Useful heat delivered (advanced): kilowatt-hours multiplied by boiler efficiency. A modern condensing boiler is around 90% efficient; an old non-condensing one may be 65% to 75%, so a quarter of the gas you pay for goes up the flue.
Source and further reading: Ofgem: energy price cap.