Gas cost calculator (UK): estimate your bill in minutes

Use our UK gas cost calculator guide to turn your meter readings (or kWh) into an estimated cost, then compare tariffs based on your postcode, meter type and payment method.

  • Works with smart and traditional gas meters (metric & imperial)
  • Shows what’s driving cost: unit rate, standing charge and usage
  • Includes examples and common pitfalls (VAT, m³ to kWh, estimates)
Get your energy quote Use the calculator steps

Estimates only. Your exact costs depend on your tariff, region, VAT and how your supplier converts gas to kWh.

Fast answer: gas cost calculator

A gas cost calculator estimates your bill by multiplying your gas use in kWh by your unit rate (p/kWh), then adding your standing charge (p/day). If your meter reads in m³ or ft³, you first convert to kWh using your supplier’s conversion (volume × correction × calorific value ÷ 3.6).

1) The core formula

Estimated cost = (kWh × unit rate) + (days × standing charge) + VAT.

2) What you need

Your tariff rates, billing period dates, and either kWh usage or meter readings.

3) What can change it

Region, payment method, meter type, billing accuracy and future price changes.

Quick caveat: Your supplier’s bill is the final authority. Calorific value varies by area and time, and standing charges can change mid-year on variable tariffs.

How to calculate your gas cost (step-by-step)

You can estimate costs from either kWh (easiest) or from meter readings. The steps below mirror how UK suppliers typically calculate gas usage.

  1. Get your dates: note the start/end dates (or number of days) for the period you want to estimate.
  2. Find your usage: use kWh from a bill/app, or subtract your meter readings to get volume used.
  3. Convert to kWh (if needed): gas meters measure volume (m³ or ft³). Bills convert to kWh using a correction factor and calorific value.
  4. Apply your unit rate: kWh × unit rate (p/kWh) = usage cost (in pence).
  5. Add standing charge: days × standing charge (p/day).
  6. Add VAT: domestic energy is typically charged at 5% VAT (unless your situation is different).

Worked scenarios (with transparent assumptions)

Scenario A: You already have kWh

Assumptions: 1,200 kWh used over 30 days; unit rate 6.20p/kWh; standing charge 31.00p/day; VAT 5%.

Usage
£74.40 (1,200 × 6.20p)
Standing charge
£9.30 (30 × 31.00p)
Subtotal
£83.70
VAT (5%)
£4.19
Total (estimated)
£87.89

Scenario B: You have meter readings in m³

Assumptions: 80 m³ used over 31 days; correction factor 1.02264; calorific value 39.2 MJ/m³; unit rate 6.20p/kWh; standing charge 31.00p/day; VAT 5%.

Convert to kWh: 80 × 1.02264 × 39.2 ÷ 3.6 ≈ 891 kWh (rounded).

Usage
£55.24 (891 × 6.20p)
Standing charge
£9.61 (31 × 31.00p)
Subtotal
£64.85
VAT (5%)
£3.24
Total (estimated)
£68.09

Your bill may use slightly different calorific values and rounding.

Tip for imperial meters: if your meter uses ft³ (often labelled “cubic feet”), suppliers convert ft³ to m³ first (by multiplying by 0.0283) before converting to kWh.

Compare gas prices for your postcode

If you want a tailored estimate, we’ll compare available tariffs for your home. This is whole-of-market comparison for UK households (not business energy).

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Only if you’d like help finalising a switch.

Used to show prices for your area (rates can vary by region).

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What affects your gas cost in the UK?

A good gas cost calculator isn’t just “kWh × price”. Your final cost depends on how your tariff is set up and how accurately your usage is measured.

Factor Why it matters What to check
Unit rate (p/kWh) The main driver of cost for heating-heavy homes. Is it fixed or variable? Any price-change dates?
Standing charge (p/day) You pay this even if you use no gas (e.g., summer months). Compare standing charge vs unit rate trade-off.
Region Ofgem price cap levels differ by region due to network costs. Use your postcode when comparing.
Payment method Direct Debit, cash/cheque and prepayment can have different rates. Are you prepay? Are you willing/able to change?
Meter type Smart meters can improve accuracy; imperial meters add conversion steps. Is your meter metric (m³) or imperial (ft³)?
Estimates vs readings Estimated bills can drift away from your true usage. Submit readings or check smart meter data.

Decision checklist: who this suits

  • If you have a recent bill and want to sanity-check your costs.
  • If you’re comparing fixed vs variable tariffs and want to model both.
  • If you’ve moved home and need a quick estimate for budgeting.
  • If you’re switching and want to understand standing charge vs unit rate.

Who it may not suit (without extra help)

  • If you’re on a complex tariff (e.g., bundled credits or special discounts).
  • If you have back-billing corrections or long estimated periods.
  • If your home is off the gas grid (you may use LPG or oil).
  • If your charges changed mid-period (you’ll need to split the calculation).

Costs, exclusions and common pitfalls

These are the main reasons a “quick” gas cost estimate can differ from your actual bill.

VAT and rounding

Most households pay 5% VAT on energy. Bills may also round kWh, pence, or apply VAT at the end, creating small differences.

m³/ft³ to kWh conversion

Calorific value varies and suppliers use values specific to your supply area and time period. Using a different value can shift results.

Price changes mid-bill

On variable tariffs, unit rates and standing charges can change. For accuracy, calculate each price period separately, then add them together.

Standing charge still applies

Even if you turn heating off in summer, the standing charge is typically billed daily. A low-usage household can be more sensitive to standing charges.

Exit fees and contract terms

Some fixed tariffs include exit fees if you leave early. A cheaper unit rate may not be best if you expect to move or switch again soon.

Important: This page covers mains gas for UK homes. It does not estimate LPG cylinders/bulk LPG, heating oil, or commercial gas contracts.

Gas cost calculator FAQs

How do I calculate my gas bill from kWh?

Multiply your kWh used by your unit rate (p/kWh), then add the standing charge (p/day × days). Convert pence to pounds and add 5% VAT for a typical domestic estimate.

Why does my gas meter use m³ or ft³, but my bill is in kWh?

Gas meters measure volume, but tariffs charge per kWh because kWh reflects the energy content. Suppliers convert volume to kWh using a correction factor and a calorific value, then divide by 3.6.

What is a standing charge and do I pay it if I don’t use gas?

A standing charge is a daily fee that covers fixed costs such as maintaining the gas network and metering. You normally pay it every day on your tariff, even if you use no gas in that period.

Do gas prices vary by region in the UK?

Yes. Network costs differ across the country, so typical standing charges and unit rates can vary by region. That’s why postcode-based comparisons are more reliable than national averages.

Is the Ofgem price cap the same as what I will pay?

Not exactly. The Ofgem price cap limits the maximum unit rate and standing charge for standard variable tariffs, but your actual bill still depends on how much gas you use and whether you’re on a fixed deal or a different payment method.

How accurate is a gas cost calculator?

It’s an estimate. Accuracy depends on using the right tariff rates, the correct number of days, and the same conversion factors your supplier uses. Variable tariffs can change rates over time, and bills may include rounding and adjustments.

Can I calculate costs for a prepayment gas meter?

Yes, but use your prepayment unit rate and standing charge, which may differ from Direct Debit prices. Your in-home display or receipts may show usage, but supplier statements are best for confirming rates.

What should I do if my bill looks much higher than my calculation?

Check the billing dates, whether rates changed mid-period, and whether the bill uses estimated readings. Compare the calorific value and correction factor on the bill, and consider sending an up-to-date meter reading. If you’re concerned, you can seek independent help from Citizens Advice.

How we assess this (methodology) + editorial transparency

Assumptions used in examples

  • Domestic VAT set at 5% for illustration.
  • Standing charge applied for each day in the period.
  • Gas conversion uses: volume × 1.02264 × calorific value ÷ 3.6.
  • Calorific value shown as an example (39.2 MJ/m³) and may differ on your bill.
  • All totals are rounded to 2 decimal places.

Limitations (what this page cannot know)

  • Your exact unit rate and standing charge (these vary by tariff, region and payment method).
  • Any mid-billing price changes, discounts, rebates or corrections.
  • Supplier-specific rounding and billing adjustments.
  • Whether you have debt repayment loaded onto a prepayment meter.

Trust signals

Last updated
July 2026

Sources (UK)

We use these references to keep guidance accurate, but rates and policies can change.

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Updated on 2 Jul 2026