How to convert electric meter reading to kWh
Learn the exact steps for your meter type (credit, prepay, smart, Economy 7) and check your bill. Includes worked UK examples, a quick formula, and the common mistakes that can inflate your estimated usage.
- Works for kWh meters and older meters that show “units”
- Clear examples for Economy 7 day/night readings
- Practical checks before you submit readings or compare tariffs
Estimates only. Your meter type and supplier billing method can affect the exact conversion. Always check your bill details and tariff terms.
Fast answer: how to convert electric meter reading to kWh
To convert electric meter reading to kWh, first work out how many units you used (new reading minus old reading). If your meter already shows kWh, that number is your kWh used. If your meter shows “units”, multiply units used by the conversion factor on your bill (often 1 unit = 1 kWh, but not always).
Key takeaway 1
Most UK electricity meters already read in kWh—you don’t convert the reading, you calculate the difference between two readings.
Key takeaway 2
If you have Economy 7 (or any two-rate tariff), calculate kWh separately for day and night registers.
Key takeaway 3
Submitting the wrong digits (or swapping day/night) can cause estimated bills or big corrections later—double-check your meter type and digit count.
Quick check: your electricity bill should state the “unit of measure” as kWh. If it does, the supplier bills in kWh even if your meter shows something like “units” or you’re using a prepayment key/card.
Conversion steps (by meter type)
Use these steps whether you’re checking a bill, giving a reading, or estimating usage before comparing tariffs. You only need two readings (old and new) and—sometimes—a conversion factor from your bill.
Step 1: Identify what your meter displays
- Smart meter (in-home display or meter screen)
- Usually shows usage in kWh. Some screens show multiple registers if you’re on a two-rate tariff.
- Digital credit meter
- Typically shows kWh and one register (single-rate).
- Economy 7 / two-rate meter
- Shows two readings (often labelled R1/R2, Low/Normal, or Night/Day).
- Prepayment meter
- Your meter still records energy in kWh (or units converted to kWh for billing). You may need to cycle the display to see the total register(s).
Step 2: Calculate units used
Formula: Units used = New reading − Old reading
- Use the same number of digits each time (most electricity meters use 5–6 digits before any decimals).
- Ignore digits in red, and ignore numbers after a decimal point unless your supplier specifically asks for them.
- If the display includes leading zeros, include them (e.g., 005421).
Step 3: Convert to kWh (only if needed)
If your meter reading is already in kWh, your kWh used is just the units used. If your meter (or bill) refers to “units”, check your bill for a conversion factor.
Formula: kWh used = Units used × Conversion factor
Where to find it: many UK bills show “Meter readings” then “kWh” directly. If there’s a factor, it may appear in the calculation lines (for example “units × 1.0 = kWh”). If you can’t see it, assume no conversion until you confirm with your supplier.
Step 4: Two-rate meters (Economy 7) — do it twice
Calculate day and night usage separately, then add them for total kWh used in the period.
- Day kWh = (New day − Old day) × factor (if any)
- Night kWh = (New night − Old night) × factor (if any)
- Total kWh = Day kWh + Night kWh
Important: “R1” isn’t always “night” and “R2” isn’t always “day”. Your bill should label which register is charged at which rate.
Two realistic UK scenarios (with numbers)
Scenario A: Single-rate digital meter (kWh)
Assumptions: you took readings 30 days apart; meter shows whole kWh; ignore decimals/red digits.
- Old reading: 18,245
- New reading: 18,457
- kWh used = 18,457 − 18,245 = 212 kWh
If your unit rate is (for example) 25p/kWh, the energy part would be estimated at 212 × £0.25 = £53.00, plus your daily standing charge and any other charges/credits on the account.
Scenario B: Economy 7 (two-rate)
Assumptions: bill labels R1 as Night, R2 as Day; no conversion factor (kWh registers).
- Night (R1) old: 06,120 → new: 06,250 → 130 kWh
- Day (R2) old: 12,980 → new: 13,185 → 205 kWh
- Total kWh = 130 + 205 = 335 kWh
When comparing tariffs, keep the split: suppliers price day and night differently, so “total kWh” alone can be misleading.
Want a tariff based on your usage?
If you have your approximate kWh (or your last bill), we can match you with whole-of-market home energy options. No pressure—your details help us return accurate quotes.
Good to know: if you’re switching, check whether your current tariff has exit fees and whether you’re in a fixed term. Your supplier will show this on your bill or online account.
Which method should you use? (Quick comparison)
In UK home energy billing, electricity consumption is charged in kWh. The table below helps you choose the right approach depending on what your meter shows.
| Meter / tariff | What the display usually shows | What you do | Common mistake |
|---|---|---|---|
| Single-rate credit | One register in kWh | New − old = kWh used | Including red/decimal digits |
| Smart meter | kWh, sometimes multiple registers | Use the register(s) your bill uses | Reading the wrong screen (e.g., instantaneous kW) |
| Economy 7 / two-rate | Two registers (R1/R2, day/night) | Calculate day and night separately | Swapping day and night readings |
| Prepayment | kWh register(s), plus credit info | Cycle screens to find total kWh register | Assuming top-ups equal usage exactly (standing charge affects credit) |
Decision checklist (who this suits)
- Good fit if you’re submitting a meter reading, checking an estimated bill, moving home, or comparing tariffs based on actual usage.
- Especially useful if you have Economy 7 and want to understand day/night splits.
- Helpful for renters who want to sense-check what they’re being billed for (you can still read the meter).
Who it may not suit (without extra help)
- If your meter has clocking issues (incorrect time on Economy 7) or you suspect the registers are mislabelled.
- If the meter is hard to access (communal cupboards) and you can’t take consistent readings.
- If your bill shows a conversion factor you can’t locate or understand—contact your supplier so you don’t submit an incorrect reading.
Costs, exclusions and common pitfalls
Converting readings to kWh is free, but the way readings are taken and billed can affect what you pay. These are the issues we see most often in the UK.
1) Confusing kW with kWh
Your bill charges kWh (energy over time), not kW (power at a moment). Smart displays sometimes show live demand in kW—don’t submit that.
2) Day/night swapped on Economy 7
If you reverse the registers, bills can look wildly wrong. Use your bill to confirm which register is “day” and which is “night”. If in doubt, take photos of both screens.
3) Wrong number of digits
Submitting too many digits (or including decimals) can create an impossible jump in usage and trigger a bill correction process.
4) Prepay top-ups aren’t the same as kWh
Your credit reduces with usage, but also with standing charge (and sometimes debt recovery). That’s why £ topped up ≠ exact kWh used.
5) Estimates, catch-up bills and payment method
If you don’t submit readings, suppliers may estimate. Later, when an actual reading is taken, you can see a catch-up bill. Your tariff and payment method (Direct Debit vs receipt of bill vs prepay) can change prices.
6) Switching timing and exit fees
If you’re converting readings for a switch, remember some fixed tariffs have exit fees. Also, the switch process uses opening/closing readings—take a dated photo for your records.
Practical tip: when you take a reading, photograph the meter screen(s) so you have evidence if there’s a later dispute about the digits or which register is which.
FAQs
Is my electricity meter reading already in kWh?
Most UK electricity meters display kWh (even older digital meters). Your bill will normally show the reading unit as kWh. If your meter shows “units”, the supplier will still bill in kWh and may apply a conversion factor shown on the bill’s calculation lines.
How do I calculate kWh used between two readings?
Subtract the old reading from the new reading. If the meter displays kWh, that difference is the kWh used. If your bill uses a conversion factor, multiply the difference by that factor to get kWh. For Economy 7, do the subtraction separately for each register.
What is the conversion factor on an electricity bill?
A conversion factor is a multiplier used to turn a meter’s “units” into kWh for billing. For many electricity meters it’s effectively 1.0 (so units equal kWh), but you should only use a factor if your bill shows one. If you can’t find it, don’t guess—ask your supplier.
How do I read an Economy 7 meter and convert to kWh?
Take both readings (day and night, often R1 and R2). Work out usage for each: new minus old. If your bill shows kWh for each register, those differences are your day and night kWh. Don’t assume R1 is always night—match the register labels to your bill’s rates.
Should I include numbers after a decimal point or in red?
Usually no. For most UK electricity meters you provide only the whole numbers (and ignore red digits or anything after the decimal). If your supplier asks for decimals, they’ll state this clearly in the “how to read your meter” instructions for your meter model.
Why does my prepayment meter credit go down even when I’m not using much?
Prepayment accounts can deduct the standing charge daily, and may also take scheduled repayments if there’s debt on the meter. That means your balance can fall even with low electricity usage. Your meter screens often show standing charge and debt settings—your supplier can explain what applies to you.
What should I do if my reading seems too high or too low?
First, check you’ve used the correct number of digits and ignored any red/decimal digits. If you have Economy 7, confirm you didn’t swap registers. Take a dated photo of the meter and compare it to your last bill. If it still looks wrong, contact your supplier before submitting the reading.
Does my kWh usage change when I switch supplier?
Your kWh usage is based on how much electricity you use, not who supplies it. What can change is the price you pay per kWh and the standing charge, which can vary by tariff, region, payment method and meter type. Your opening and closing readings help make the final and first bills accurate.
Trust, methodology and sources
Page ownership
- Written by:
- EnergyPlus Editorial Team
- Reviewed by:
- Energy Specialist
- Last updated:
- July 2026
How we assess this (our methodology)
This guide is based on how UK suppliers bill electricity consumption in kilowatt-hours (kWh) and how household meters typically present readings (single-rate, multi-rate, smart, and prepayment). We prioritise steps that reduce common reading errors that lead to estimates, catch-up bills, or incorrect day/night allocation.
- Assumption: you’re converting electricity meter readings for a UK domestic supply (not business).
- Assumption: you have at least two readings taken at different dates (or a bill showing previous readings).
- Limitations: some meter models label registers differently; Economy 7 timings vary by region and meter configuration; and some suppliers present “units” but still bill in kWh using an internal factor stated on the bill.
- What we don’t do: we don’t estimate your bill total here because standing charges, regional prices, VAT, discounts/credits, and payment method can change the final amount.
Transparency: if your bill shows a conversion factor (or your meter is labelled unusually), follow the bill’s calculation lines first. When in doubt, confirm with your supplier before submitting a reading.
Ready to compare based on your kWh?
Use your latest reading difference (and day/night split if you have Economy 7) to get quotes. Results vary by region, meter type, payment method and tariff terms.
Back to Guides & FAQs