A practical worksheet · Updated 2 November 2026 · Free Carbon Calculator
A high bill tells you how much electricity you bought. It does not tell you which appliance used it. This seven-day exercise helps you build an evidence-based shortlist before buying a replacement appliance or assuming that every unexplained unit is waste.
Use a bill, a notebook and appliance labels you can safely read. An appliance energy meter is optional. You do not need to buy equipment to use the worksheet.
1. Establish the bill boundary
Write down the billing dates, number of days and billed kWh. Divide units by days to find the average per day. A 300-unit bill for 30 days represents 10 kWh/day. A 300-unit bill for 35 days represents about 8.57 kWh/day. Compare the daily figures before concluding that use increased.
If you have solar or backup power, identify whether the figure is grid imports, net imports or total household consumption. A grid bill alone may omit electricity supplied directly by solar. Record outages, guests and changes in occupancy because they affect comparisons.
2. Mark the evidence behind each estimate
- Measured: cumulative appliance kWh over a stated period.
- Label-based: annual kWh from the exact model, converted to the required period. This is a standardised comparison, not a measurement of your home.
- Assumed: estimated average watts or hours. Keep these editable and visible.
For a reasonably steady load, kWh = watts × number of appliances × hours ÷ 1,000. For equipment that cycles or varies its input, use cumulative energy or a suitable label instead of multiplying maximum watts by every hour it is plugged in. See our separate fridge and inverter AC workflows.
3. Work through one transparent example
The following is an invented household worksheet, not a survey, measured case study or promise of savings. The 50-per-unit price is illustrative and excludes charges that do not change when units fall.
| Change and assumption | Calculation | Units avoided | At 50 per unit |
|---|---|---|---|
| Two 60 W fans, one less hour each day when the room is empty | 2 × 60 × 1 × 30 ÷ 1,000 | 3.60 kWh | 180 |
| A measured 5 W nonessential standby group, off for 12 hours/day | 5 × 12 × 30 ÷ 1,000 | 1.80 kWh | 90 |
| One 1,000 W iron, 6 fewer minutes/day through batching | 1,000 × 0.1 × 30 ÷ 1,000 | 3.00 kWh | 150 |
| Total, if independent and achievable | 3.60 + 1.80 + 3.00 | 8.40 kWh | 420 |
Against a 300-unit baseline, these changes would leave 291.6 units, a 2.8% reduction. This modest result is useful: it prevents a small standby load from being presented as the explanation for an entire bill. The iron example only applies if its actual energised time falls by six minutes; switching the appliance on for six fewer minutes does not prove the heating element ran continuously during that time.
4. Reconcile without forcing the answer
Add the estimates for the same period. If the sum exceeds your bill, check duplicated appliances, watts versus kilowatts, hours and whether a maximum rating was treated as an average. If the sum is lower, note the gap. It may reflect unlisted loads, uncertain runtimes, water heating or the solar boundary. Do not automatically label the gap a leak or theft, or rescale every appliance to make the total fit.
5. Change one thing and keep a seven-day log
| Date | Start/end meter kWh | AC or heating hours | Occupancy, weather and outages | One change tested |
|---|---|---|---|---|
| Day 1–7 | Record readings at the same time | Record settings too | Note unusual conditions | Describe exactly |
A whole-home meter shows the combined result of everything operating. A lower reading on a cooler day cannot establish the effect of changing a fan. Repeat under comparable conditions and describe the result as an observation, not proof of causation. Never open the meter, distribution board or appliance casing to collect readings.
6. Rank changes before spending
Start with unused operating time and settings that preserve comfort. For a purchase, compare useful service, expected annual units and the extra purchase cost. Simple payback = extra cost ÷ annual avoidable energy-charge reduction. If a replacement costs 12,000 more and saves 2,000 a year, the illustrative payback is six years, before maintenance, financing or price changes. A working appliance is not automatically worth replacing.
Use the bill and device estimator to enter your own assumptions. For a broader partial energy and travel estimate, use the personal calculator. Do not add the two tools' totals together.
Sources and calculation notes
The unit calculation follows the US Department of Energy's Energy Efficiency at Home educational module. The worksheet, numerical scenario and reconciliation approach above are this site's explanatory examples. They are not measured research data. Carbon conversions require a clearly identified electricity factor and source year; our methodology explains the boundaries.
This page replaces the earlier general “five hidden traps” list with a specific household-energy workflow. Found an error? Send the page URL, inputs and expected calculation through our contact page.
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