SizingKitEnergy & cost
Energy usage calculator
Six loads entered with honest running hours come to 472 kWh, the meter for the same 30 days registered 638, and the 166 kWh in between is the answer worth having: expressed as a steady draw it is 231 W running in that building every hour of the month, and finding it is worth more than any of the six. This page is an attribution rather than a total — the meter already gave you the total — so it ranks every load by its share of the period and prints what the list fails to explain as its own line. It is deliberately built around the one number nobody can look up: how many hours a day each machine is genuinely drawing power rather than merely switched on.
- 100% free
- No signup
- 20 rows
- Ranked by share
- Remainder as watts
What is in the building, and how much of the period it spends drawing
Hours are running hours, not switched-on hours. Anything with a thermostat spends most of the hour idle, so a 4,500 W water heater goes in at the two or three hours a day its element is actually energized. Days lets a dryer be entered as twenty days rather than thirty.
| What it is | No. | Draw | h/day | Days | kWh | Remove |
|---|---|---|---|---|---|---|
| 338 | ||||||
| 28.8 | ||||||
| 42 | ||||||
| 31.7 | ||||||
| 15.8 | ||||||
| 16.2 |
What the meter says
The figure the list is checked against. Everything the list fails to explain shows up below as a remainder.
Optional. Divide the bill total by the kilowatt-hours above and you have it for this period exactly.
Where the period went
ACCOUNTED FOR
472 kWh
NOT ACCOUNTED FOR
166 kWh
| Ranked | kWh | Share | Cost |
|---|---|---|---|
| Electric water heater | 338 | 52.9% | — |
| Clothes dryer | 42 | 6.58% | — |
| Desktop and two monitors | 31.7 | 4.97% | — |
| Refrigerator, compressor running time | 28.8 | 4.51% | — |
| LED lighting through the house | 16.2 | 2.54% | — |
| Well pump | 15.8 | 2.47% | — |
| Nothing on the list explains this | 166 | 26% | — |
- The remainder as a steady draw
- 231 W · 787 BTU/h
- Metered average a day
- 21.3 kWh
- The period as energy
- 2,297 MJ
- Rate applied
- —
What carried the period: Electric water heater did, at 52.9% of the period. Halving its hours moves the bill by 26.4%, which is more than anything below it on the list can offer.
How to go and find it: a remainder of 166 kWh over 30 days is the same as something drawing 231 W without stopping. Read the meter last thing at night and first thing in the morning with nothing deliberately running: the overnight rate is the building's floor, and anything above about a tenth of a kilowatt-hour an hour has a cause you can switch off one breaker at a time.
Where this survey is weakest. In the hours column, every time. Nameplate watts are printed on the machine and the count is in front of you, but how long the water heater's element was actually energized last month is a guess unless something measured it. A circuit-level monitor at the panel or a plug meter moved around the house for a week turns the largest three rows from estimates into readings, and the ranking stops moving after that.
How to work out where a bill actually went
An audit that reconciles is worth ten that add up. Enter the loads, then enter the meter, then argue with the gap.
List the loads in duty-cycle hours, not switched-on hours
Every row is a count, a draw and the hours a day that draw is real. A refrigerator is plugged in for 24 hours and its compressor runs for perhaps eight of them, so eight is the figure. An electric water heater's element is energized for two or three hours a day in an ordinary household and nothing like 24. Getting these wrong in the same direction across six rows is how an audit ends up explaining 200% of a bill.
Give the period the days the bill gave it
Read the number of days between the two meter reads off the bill rather than assuming a month, and give any load that does not run through the whole period its own day count — a dryer used four times a week is twenty days, not thirty. Leaving the days column blank hands the row the whole period, which is the right default for anything continuous.
Enter the metered kilowatt-hours and look at the remainder
The gap between your list and the meter is the finding. A remainder much larger than your biggest listed load means the biggest single item on this bill has not been entered at all, and the wattage printed beside it tells you what to look for: a steady two or three hundred watts is a second refrigerator, a pool or circulation pump, a well pump short-cycling on a failed pressure tank, or a heat trace circuit somebody energized in November and never switched off.
Technical specifications
| Row shape | Count, draw, running hours a day and days in the period — four fields, multiplied. The count column exists so twelve identical light fittings are one row rather than twelve, and it takes fractions if you want to say that half the fixtures are on. |
|---|---|
| Rows available | Twenty. Past about eight the survey stops improving, because the tail rows are smaller than the error in the hours you assigned to the top three. |
| What the reconciliation is done in | Kilowatt-hours, never dollars. A bill total also contains fixed charges and taxes that no appliance produced, so comparing energy against energy is the only comparison that can close exactly. |
| The remainder as a wattage | The unexplained kilowatt-hours multiplied by 1,000 and divided by the period's hours — 166 kWh across 30 days is 231 W, held continuously. This conversion is the whole point of the reconciliation: an accounting gap is abstract and a wattage is something you can go and hunt with a clamp meter. |
| How shares are calculated | Against the metered figure when you have supplied one, and against the list's own total when you have not. The two denominators are different questions — share of the bill against share of what you listed — and the page uses the stronger one whenever it exists. |
| A negative remainder | Reported as its own case rather than hidden. A list that exceeds the meter is not a metering fault; it means something was entered at its nameplate for hours it spends cycling, and the page says so. |
| Deliberately not modeled | Weather correction, so two months are not directly comparable until you divide by degree days; and the standby draw of each individual device, which is a per-appliance question rather than a whole-building one. |
| Where the survey is stored | In the browser tab and nowhere else — no account, no upload, no file written, and closing the tab is how it is deleted. |
Frequently asked questions
My list is well short of the bill. Is the meter over-reading?
Almost certainly not — revenue meters are type-approved, tested at commissioning and drift very little, and the failure mode when they do drift is usually to under-register. A shortfall of a quarter or a third is the normal result of a first audit, and it is telling you that a real load is running that you have not thought of. Continuous loads are the ones that hide, because nothing about them is memorable: they make no noise, nobody switches them on, and they were probably installed by somebody else.
My list adds up to more than the bill. Where is the error?
In the hours column, on whichever row has the biggest wattage. Anything thermostatically controlled spends most of the hour off, so entering a 4,500 W water heater or a 3,500 W air handler at its plate for every hour it is available produces a figure several times the truth. The other common version is counting a heat pump at its resistance backup rating, which it only reaches on the coldest mornings of the year.
How do I actually find a continuous 231 W?
Read the meter twice overnight, then start switching things off. With nothing deliberately running, the difference between a reading at midnight and one at six shows the building's floor directly — divide by six and you have the standing wattage without any arithmetic about appliances at all. If that floor is large, open the panel and pull one breaker at a time with an hour between each, or clamp the individual circuits if you have the meter for it; the circuit that drops the floor is the one to investigate.
What counts as a running hour for something that cycles?
The fraction of the hour the load is drawing power, multiplied back out to hours a day. A compressor that runs twenty minutes in every hour is on for eight hours a day whether or not anybody opened the door; a well pump that refills a pressure tank for four minutes an hour is on for 0.7 hours. If you cannot estimate it, measure one hour with a plug meter and multiply — a single hour of observation beats any amount of reasoning about duty cycles.
Why does the page rank loads by kilowatt-hours rather than by cost?
Because on any single rate they rank identically, and where they do not, the cost ranking is misleading. Under a time-of-use schedule the same kilowatt-hour is worth two or three times as much in the late afternoon as at three in the morning, so a load that ranks fourth by energy can rank first by money — but only if you know when it ran, which a survey of this shape cannot tell you. Ranking by energy makes an honest statement; ranking by cost would make a confident one.
How many appliances should I list before the answer is good enough?
Until the next row you would add is smaller than your uncertainty about the rows already there. In practice that is five to eight items in a house, because domestic consumption is enormously top-heavy — water heating, space conditioning, laundry and refrigeration usually carry most of it, and everything else is a long tail of tens of kilowatt-hours. Spending an evening estimating the phone chargers while the water heater's hours are a guess is effort in the wrong place.
Can I reconcile against the dollar amount instead of the kilowatt-hours?
Not directly, and that is why this page asks for energy. The dollar total on a bill includes a fixed charge that no appliance caused, taxes and fees applied afterwards, and on a stepped schedule a price that changes partway through the month — none of which any load list can reproduce. Close the reconciliation in kilowatt-hours first, and only then apply a rate; the kwh cost calculator works out which rate that should be.
About attribution, and why the remainder is the interesting number
Load surveys go wrong in one place, and it is not the one people expect. Nameplate wattages are printed on the equipment and generally honest; counts are in front of you; the arithmetic is a multiplication. What nobody can look up is the duty cycle — the share of each hour a thermostatically controlled machine spends actually drawing power — and that single unknown swings the answer further than every other input combined. A 4,500 W water heating element entered at four hours a day rather than two and a half is 202 kWh of pure invention over a month, which is larger than most of the rest of the list put together. This is why the page reconciles at all: an audit that only adds up can be wrong by a factor of two without ever looking wrong, and one that is checked against the meter cannot.
The remainder that falls out of that check is usually large, and it is usually continuous rather than dramatic. Loads that run hard announce themselves — you hear the dryer, you notice the shower — whereas the things that run all the time are the ones nobody thinks to mention, and they get four to six times as many hours as anything else in the building. That asymmetry is the same one the electricity cost calculator makes for a single machine when it separates standby from running, and it is worth internalizing as a rule of thumb: a watt that never stops is 8.76 kWh a year, so any steady hundred watts you find is 876 kWh you have been buying without knowing what for. Once the gap closes, converting the ranked kilowatt-hours into money needs the blended figure from the kwh cost calculator rather than the headline rate, because the fixed charge belongs to the bill and not to any appliance on the list.
Two things a survey like this cannot settle on its own are worth naming. The first is season: a bill that doubles between October and January is not an appliance problem at all but a fabric one, and what a building loses through its walls and its air changes is worked out on the heat loss calculator, which is also where the argument about insulation belongs. The second is that this same list, read differently, answers a completely different question — asked for its starting rather than its running watts, it sizes standby power, because a motor draws several times its running current for the second it takes to come up to speed and that surge, not the monthly total, decides the machine on the generator size calculator. The transportation load is the third case, and it is separate again because a car is charged rather than run: that arithmetic, including the tenth of the energy that never reaches the battery, is on the ev charging cost calculator.
Where the survey of the building goes
Every number on this page is worked out by JavaScript running in the tab you are reading it in. Nothing you type — loads, lengths, nameplate ratings, the rates your utility charges you — is uploaded, logged or kept, which is also why the calculators carry on working in a mechanical room with no signal.
A load list is a description of how a building is occupied — when people are home, when they wash, when they are away. It is assembled and ranked entirely inside this tab, and no part of it, and no meter reading you enter beside it, is transmitted or stored anywhere.