Electrical power/ CALCULATOR

Grid import from two electricity meter readings

Calculate the change in one cumulative import register, its daily average, mean imported power and an entered-rate energy charge. This is not a complete bill or household demand model.

Initial cumulative import reading R₁kWhSame identified meter and import register, in actual kWh. Not export, instantaneous kW or a money balance. Resolve any multiplier with the supplier first.

Final cumulative import reading R₂kWhSame register and units, at the end time. A lower value needs a replacement/reset/rollover check; do not take an absolute difference.

Actual elapsed time thUse the actual interval between timestamps. Fourteen exact 24-hour days are 336 h; clock changes or missing readings need care.

Entered energy-only price pcurrency units/kWhFictional default, not a current tariff. Enter your chosen currency units per kWh, not cents/pence unless converted. A zero price gives zero energy charge only; fixed fees remain outside the estimate.

Recorded imported energy

141.500 kWh

Average import per 24 hours

10.11 kWh/day

Mean imported power over the interval

421.13 W

Energy-only amount at entered price

28.30 currency units

One unchanged cumulative import register, actual kWh and elapsed hours, with one entered nonnegative energy price. No export credit, net metering, separately added taxes, standing charges, debt, fixed fees or time-of-use allocation. Import may be only part of household electricity when there is PV or storage. Mean power is not peak demand. Decimal output does not improve meter resolution; no current tariff is supplied.

FROM ESTIMATE TO ACTION

Use the result, not just the number.

Choose the same import register

Read only an already installed, safely accessible display or an authorized record. Do not open a meter enclosure, break seals, expose terminals or change settings. If access is unsafe or a display is unclear, ask the supplier for help. Keep meter serial, exact register name, unit and any supplier-confirmed multiplier. Import and export are separate quantities. On multi-rate meters, retain each register separately; do not add a total register to its own rate subregisters. The linked supplier instructions concern UK models, not a universal button sequence or colour rule.

Retain two actual readings and the real time interval

Record both timestamps, timezone and full readable cumulative kWh. Identify estimated or missing values instead of treating them as measurements. After replacement, reset or rollover, split the record into documented intervals; a lower final reading is not made valid by removing its minus sign. For the calculator, enter actual elapsed hours. A fictional 14 × 24 h interval is 336 h; calendar dates spanning a clock change need their actual elapsed duration. Keep the readable increment: three displayed result decimals do not prove sub-kWh measurement precision.

Keep the selected energy charge separate from the bill

The price is entered by the reader; the default is fictional. One 141.5 kWh interval at 0.200 currency/kWh gives 28.30 energy-only units. Convert cents or pence consistently before entry. This does not select a tariff or predict a supplier’s account balance. When prices differ by register or time, calculate matched energy segments at their own rates. For example, 90 kWh × 0.20 + 51.5 kWh × 0.10 = 23.15, not 141.5 × 0.20 = 28.30. Use non-overlapping records; if the necessary breakdown is unavailable, this calculator cannot reconstruct it. Fixed charges and other billing items remain separate even with zero recorded import.

Inputs to verify

Initial cumulative import reading R₁ (kWh): Same identified meter and import register, in actual kWh. Not export, instantaneous kW or a money balance. Resolve any multiplier with the supplier first.
Final cumulative import reading R₂ (kWh): Same register and units, at the end time. A lower value needs a replacement/reset/rollover check; do not take an absolute difference.
Actual elapsed time t (h): Use the actual interval between timestamps. Fourteen exact 24-hour days are 336 h; clock changes or missing readings need care.
Entered energy-only price p (currency units/kWh): Fictional default, not a current tariff. Enter your chosen currency units per kWh, not cents/pence unless converted. A zero price gives zero energy charge only; fixed fees remain outside the estimate.

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