How to work out gas readings and usage from M3 and kWh?

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Hi. New to Ovo so just looking for some help to understand the readings below.

It says:

Opening reading on 7 july estimated 5157

Closing reading as of 28 july (you gave) 5177

Units used 221.15 kWh.

Am I looking at this wrong because surely the difference between these readings is 20 not 221.15???


Best answer by TomThumb 8 August 2022, 00:49

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Userlevel 1

I would contact them with alacrity. You are quite correct that's surely only 20 units used.

I had to wait nearly 3 weeks to get a refund for monies wrongfully taken from my account.


Kindest regards from Clive 

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Actually, gas meter readings are usually done in M3 (Meters Cubed) and then converted to kWh by the billing platform. This is unlike electric meters which always record using kWh directly.

I ran the conversion myself using one of my tools and got the result 223.7355, so your result from OVO of 221.15 seems about right to me.

You are right though. Based on your question, you did seem to only use 20 M3 of gas during that period, but it’s the kWh conversion result that matters and this has to be generated using a specific formula that I can never recall. Given that the conversion spits out 223.7355 for me (and doesn’t factor in the Calorific Value), I’m pretty confident you were billed correctly.

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Updated on 28/07/23 by Abby_OVO

@Tjw50 Hope I can shed some light on this for you,

In short, Metered units are not the same as kWh units, 

Units    Calorific value  X    1.02264  ~  3.6    =  kWh

20       X    39?                  X    1.02264    ~ 3.6 = 221.5 kWh

(this close to midnight I think my maths is ok) lol

(although I couldn’t find the divide symbol 👀)



The conversion as stated by ovo is


We convert your metered gas units to kWh using the following formula:
Metered volume × metric conversion factor1 × daily calorific value2 × 1.02264 (volume correction) ÷ 3.6 = kilowatt hours (kWh) used.
1 We convert the gas use into kWh according to your meter type – 2.83 (imperial) or 1 (metric).
2 The calorific value of gas changes every day and can range from 37.5 to 43.0. To find out calorific values used to calculate your charges you can visit: value-cv


Userlevel 1

Thanks everyone

Hi ,


 I’m trying to understand where the charges for 2577.789 kWh in Gas is coming from .. I’ve been going through both the usage ever since we moved in, with the meter reading we gave and I’m not sure what OVO did. Of course can’t get any support from them to get it rectified. 

if anyone has an idea where it could be from ? 



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Your gas reading has to be converted to get the kWh data. Your bill shows this 

As a rough calculation from your meter, it looks about right. The kWh is then used along with your unit rate to calculate your bill

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To be honest, as @BPLightlog says, if those meter readings are correct, it really doesn’t look like there is anything to rectify.



Hi ,


Thanks for the answers i did some research and calculation, it seems to be correct. 

Was a bit shocked at first but i guess i need to adjust the Heating system. 


Thank you :) 

How do I convert my units of gas used into kWh ? Am using the formula suggested where you take the units used x1.02264 then x30 then divide by 3.6...doesnt tally with that on my bill. I have units used as 49 and a bill of £153.42. is that correct? Please advise. Am very confused.

Oops...meant to say x1.02264 then X 39 then divide by 3.6....

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Hi @Pappi you need to use a caloric value in the calculation (that might be what you meant by x39). Is your gas meter a metric one (reading in cubic meters?) the cost you mention suggests not so there’s another x2.83 in the mix, unless that’s the part that’s wrong. 
49 units x 2.83 x 39 x 1.02264 divided by 3.6 gives 1536.27 which at around 10p per kWh would make £153.62

The calculation is shown on your bill like this -

After that you need to multiply the result by your price per kWh from your plan

That makes sense now.... looked again and it does say ft3 so it must have been an imperial measuring unit. Thanks for this. Trying to be more aware of usage. Thanks again.

Don’t forget the correct calorific value to use.

We convert your metered gas units to kWh using the following formula: Metered volume × metric conversion factor × daily 1 calorific value × 1.02264 (volume correction) ÷ 3.6 = 2 kilowatt hours (kWh) used. 1 We convert the gas use into kWh according to your meter type – 2.83 (imperial) or 1 (metric). 2 The calorific value of gas changes every day and can range from 37.5 to 43.0. to calculate your charges you can visit:

I have this morning received a call direct from OVO following the questions I raised before about the actual calorific value used to calculate a bill.

I was asked how I arrived at my costs to date and they did their calculations which found both sets of costs were the same.

I gave them the way that I have evaluated the use of the averages on a daily basis to see if there were any erroneous assumptions on my part. There were not and the way that the CV data is issued daily, then daily averages calculated by OVO and re-evaluated as and when  the National Grid data is adjusted, sometimes daily, sometimes weekly, is exactly the way I had been calculating my usage costs on a daily basis.  It is a tedious process that OVO have to deal with, and consumers with interest have to get their heads round. It does mean, for a customer, backtracking over the CV data issued to modify the data as necessary.

From the above it is actually possible to correctly calculate usage/costs.

Reverse calculation is possible once a bill is issued, to calculate the CV. All it means is to vary the CV used until your costs tally. Again tedious. Easier for me as I have set up daily automatic variations.

Also I now will have further details showing how OVO process this section of costings. 

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It’s fairly easy to reverse calculate the average cv for a bill .. take a recent one of mine which had a metered volume of 269.481 and a kWh figure of 3004.105

I can see my cv average used .. if I take my metered volume 269.481 x 1.02264 divided by 3.6 = 76.5505694 

Take the total kWh units of 3004.105 divided by 76.5505694 gives 39.24340502684752 which will be the average of the daily cv ratings used for that bill

BPLightlog You are spot on. I think you will agree though, that it is rather tedious and for those who can’t do it. The answer may be to sometime in the future make the CV available so a simple multiplication/division calc. would suffice.

I can, after my discussion today understand  why the OVO system does not at present show the CV events.

Good answer though, showing clearly the sequence to follow to arrive at the CV used.

Userlevel 7


The Government provides detailed guidance on how to read your gas meter and convert this reading to kilowatt hours: Gas meter readings and bill calculation - GOV.UK



It’s not clear, though, how the CV calculation is made by OVO billing, which prides itself on being ‘live’ with account status updated daily for most users. This makes sense when smart meters submit meter readings every day. Consumption in kWh can then be calculated using each day’s published CV¹. It presents a problem, though, when billing has to rely on manual readings submitted by the consumer, especially those who are used to reading the meter at longer intervals - e.g. weekly or quarterly. Two possibilities in this scenario are:

  • The average daily usage for the billing period is estimated on the basis of the last few known readings, and then each day’s conversion takes place at that day’s published CV, or
  • The total usage in the billing period is estimated on the basis of the last few known readings, and then the conversion for the whole period takes place at the average CV for the period, using the formula in the regulations².

These would, I think, produce identical results at the end of the period and thus have no influence on the bill, but the results shown on any day within the period could conceivably vary quite considerably. It also explains why it’s not simple to quote ‘the actual calorific value used to calculate a bill’.

Has anyone worked out how OVO do it? 




  1. “Gas transporters are required to maintain this figure within 38 MJ/m³ to 41 MJ/m³ ...”
  2. “The average calorific value of gas so conveyed during any such gas period shall be calculated by adding the daily calorific values … for each gas day in that gas period and dividing the sum by the number of those gas days ...”


Again you are correct Firedog in saying “It’s not clear, though, how the CV calculation is made by OVO billing”. My discussion with the OVO team this morning did however explain how the CV is taken from National Grid data at daily frequencies depending on the timing of the data release and and adjustment to the CV figure, followed by averaging to give usages. 

They actually used my data this morning from my readings beginning 1st Jan and it confirmed their correct method of using CV data then averaging to calc. usage.

The problem at the moment is OVO system is not able to show the workings of the system. May be able to in the future.

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I have copies of earlier bills from the 1980’s where there was a CV printed on the bill. Remember this was for a quarter at that time so presumably there were no ‘daily readings’ back then. 
I have to admit that I was even at that time looking very closely at how this was all calculated with BTU’s (British Thermal Units) used to provide the different value determined for gas supplied.

I moved to Ovo in the middle of November and the billing calculation doesn’t stack up to me, but there is every change I’m missing something!

See below bill summary. Any ideas why my meter readings below show 115 kWh of gas usage but this multiplied by 10 by Ovo to arrive at 1,156.36 kWh of usage?


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It’s all to do with calorific value @emeraldovo 

Details are shown on your bill as above. The gas meter reads in cubic metres which need to be converted to kWh