Gas Bill Calculator
Estimate your gas bill from MJ or cubic metres, your usage rate and daily supply charge, with heating value and pressure factor conversion.
Only used for cubic metres. Copy it from your bill; it is often about 38–39.
Only used for cubic metres. Use 1 if your bill does not show one.
Your results
Calculation breakdown
- Megajoules from cubic metres
- MJ = m³ × pressure correction factor × heating value
- Usage charge
- Usage charge = MJ used × rate per MJ
- Supply charge
- Supply charge = daily charge × days
- GST (optional)
- 10% of usage + supply charges when rates exclude GST
Worked example
Using 6,000 MJ over a 90-day quarter at 2.7c/MJ, plus a 90c daily supply charge, gives an estimated bill of $243. A meter reading of 150 m³ with a heating value of 38.5 MJ/m³ and a pressure factor of 1 is 5,775 MJ.
Assumptions
- Retail gas rates are usually quoted including GST; only switch on the GST option if your rates exclude it.
- Uses one usage rate; if your plan has stepped rates, calculate each block separately.
- Actual bills may include discounts, concessions or other fees not modelled here.
How this calculator works
Enter your gas usage in megajoules (MJ) for the billing period, your retailer's usage rate per MJ and the daily supply charge to estimate your total gas bill. Gas usage on bills is often shown in MJ rather than cubic metres, so a conversion factor is included.
Estimate a gas bill from your meter reading
Australian gas is charged by the megajoule (MJ). If your bill or meter shows cubic metres, the calculator converts the reading using the heating value and pressure correction factor printed on your bill: MJ = cubic metres × pressure correction factor × heating value.
The usage charge is the megajoules used multiplied by your rate per MJ, and the supply charge is the daily charge multiplied by the days in the billing period. With 6,000 MJ at 2.7 cents per MJ and a 90-cent daily charge, a 90-day bill is $162 plus $81, or $243.
Seasonal use, step rates and GST
Gas use for heating rises sharply in winter, so compare a winter bill with the same quarter last year rather than with a summer bill. Some plans charge a higher rate for the first block of megajoules and a lower rate after that; calculate each block separately if yours does.
Retail gas rates are usually quoted including GST. Only switch on the GST option when your rates are shown excluding GST, such as on some business offers, or the estimate will be about 10% too high.
Official sources and assumptions
Check the official or authoritative references used to review this calculator's rates, formulas and assumptions.
Frequently asked questions
My bill shows cubic metres, not MJ, what do I do?
Choose cubic metres and enter the heating value and pressure correction factor shown on your bill. The calculator converts the reading to megajoules before applying your rate.
Does this include GST?
Toggle the GST switch on if your entered rates are GST-exclusive; most retail bills already include GST in the quoted rate.
Why does my bill vary by season?
Gas usage for heating rises sharply in winter, so seasonal usage figures give a more realistic estimate than an annual average alone.
Content responsibility
Maintained by CalcAussie and last updated 3 November 2026. Checks applied: calculation method, worked examples, Australian terminology, material assumptions, official references where an external rule applies, and user-facing limitations.
Calculator results remain estimates based on the figures entered. Check material decisions against current official information and report a suspected error so it can be reproduced and corrected.
Actual prices, usage, efficiency and savings vary by provider, equipment, location and behaviour.