Gas Bill Calculator

About the Gas Bill Calculator

Reading a gas bill can feel like decoding a puzzle. The meter measures a volume of gas — cubic metres, or hundreds of cubic feet — but the bill charges for energy, in kilowatt-hours or therms. Between the two sit a correction factor, a calorific value that changes from month to month, a unit rate, a daily standing charge and tax. Checking whether a bill is right, or estimating the next one from your own meter readings, means working through every step.

This gas bill calculator does it for you. Enter your previous and latest meter readings, choose what the meter reads in — cubic metres, hundreds of cubic feet on a UK imperial meter, CCF on a US meter, therms or kWh — and enter the unit rate, standing charge, days in the billing period and tax. It gives the bill, the energy used in kWh and therms, a full breakdown, the cost per day and your average daily use.

How to Use the Gas Bill Calculator

Choose what your meter reads in. It is usually shown on the meter face: "m³" for a metric meter, "ft³" or "cubic feet" for an imperial one.

Enter the previous reading and the latest reading, ignoring any red digits or digits after the decimal point.

For metric and imperial meters, enter the calorific value from your bill.

Choose whether your price is per kWh or per therm, and enter the unit rate, the standing charge per day, the days in the period and the tax rate.

How the Gas Bill Is Worked Out

  gas used      =  latest reading − previous reading
  m³            =  gas used          (× 2.83168 for hundreds of cubic feet)
  kWh           =  m³ × 1.02264 × calorific value ÷ 3.6
  therms        =  kWh ÷ 29.3071     (US: 1 CCF ≈ 1.037 therms)
  gas cost      =  kWh (or therms) × unit rate
  standing      =  days × standing charge
  bill          =  (gas cost + standing) × (1 + tax)

Step-by-Step Example

A metric meter from 1,000 to 1,100 m³, calorific value 39.5, 0.06 per kWh, 0.30 a day standing charge, 30 days, 5% VAT.

  Gas used:   1,100 − 1,000                  =  100 m³
  Energy:     100 × 1.02264 × 39.5 ÷ 3.6     =  1,122 kWh  (38.3 therms)
  Gas cost:   1,122 × 0.06                   =  67.32
  Standing:   30 × 0.30                      =  9.00
  VAT:        76.32 × 5%                     =  3.82
  Bill:       76.32 + 3.82                   =  80.14

A US meter using 50 CCF at 1.40 a therm.

  Energy:     50 × 1.037                     =  51.85 therms
  Gas cost:   51.85 × 1.40                   =  72.59

What the Numbers on a Bill Mean

The correction factor, 1.02264, adjusts the volume measured at the meter to standard temperature and pressure, because gas expands and contracts.

The calorific value is the energy content of the gas, in megajoules per cubic metre. It varies slightly with the source of the gas, usually between 38 and 40, and the figure used appears on your bill.

Dividing by 3.6 converts megajoules to kilowatt-hours, because one kWh is 3.6 MJ.

The standing charge is a fixed daily amount for the network and meter, paid whatever you use.

Therms are the US and older UK unit: one therm is 100,000 British thermal units, or about 29.3 kWh.

Reading Your Meter

Most metric meters show five black or white digits followed by red digits or a decimal point; record only the digits before the red ones. Imperial meters usually show four digits. Some older meters have dials: read each dial in order, taking the lower number when the pointer is between two. Smart meters send readings automatically, but the display can still show the reading, which is useful for checking.

Estimated Bills

When a supplier has no recent reading, it estimates your use, often from the same period last year. Estimates can be well above or below the truth, especially after a change in the weather, the household or the boiler. Submitting actual readings regularly — ideally on the date the bill is produced — keeps bills accurate and avoids a large catch-up bill later.

Cutting Your Gas Use

Heating is usually by far the biggest use of gas in a home. Turning the thermostat down by one degree can save around 10 percent on heating costs. Heating controls and timers, radiator valves on unused rooms, draught-proofing and insulating the loft and walls all cut use substantially. Lowering the flow temperature of a condensing boiler helps it run more efficiently, and a regular boiler service keeps it running well.

Comparing Tariffs

Tariffs trade off the unit rate against the standing charge. A tariff with a low unit rate and a high standing charge suits a household that uses a lot of gas; one with a higher unit rate and a low standing charge suits a small flat or a home that uses gas only for cooking and hot water. Enter your yearly use with each tariff's figures, setting the days to 365, to see which is cheaper for you. For example, 10,000 kWh a year at 0.06 plus 0.30 a day costs 709.50 before tax, while the same use at 0.065 with no standing charge costs 650.00.

Gas in Summer and Winter

Most homes use several times more gas in winter than in summer, because heating dominates. Monthly bills that seem high in January and low in July are normal.

Understanding Your Result

Gas bill is the total for the billing period.

Energy used gives the kWh and therms.

Breakdown shows the gas cost, standing charge and tax separately.

Per day gives the average cost per day.

Average use shows the kWh used per day.

Worth knowing explains the value of actual meter readings.

When Should You Use This Calculator?

Checking a gas bill for errors.

Estimating the next bill from your own readings.

Comparing tariffs with different unit rates and standing charges.

Tracking heating use week by week in winter.

Converting between m³, CCF, therms and kWh.

Common Mistakes

Including the red digits from the meter.

Choosing the wrong meter type, metric or imperial.

Forgetting the standing charge.

Mixing up prices per kWh and per therm.

Relying on estimated readings.