Kilowatts to Kilowatt-Hours Calculator
My well pump draws 4 kW while it's actually running, and it kicks on for roughly 6 hours across a typical day. What does that add up to by the time a month closes out? That's the gap this page closes: a kilowatt figure is a rate, not a total, and the only way to turn it into an amount of energy is to multiply by how long the load actually runs.
kWh = 4 × 6 = 24.00 kWh
Rate versus total: why kW and kWh diverge
A kilowatt describes how fast energy is being used at a single instant, the way miles per hour describes a speed. A kilowatt-hour is the running total that speed produces once time is factored in, the way a trip odometer accumulates distance. A 4 kW pump and a 0.15 kW fridge are not directly comparable on power alone; what actually shows up on an energy bill depends on how long each one runs.
That's the entire formula: no power factor, no voltage, nothing to look up. The only input worth double-checking is the hours figure, because it has to reflect actual run time, not just the hours a device sits plugged in. A well pump, a space heater on a set schedule, or an EV charger mid-session run close to their full rated hours; a fridge, an HVAC compressor or anything on a thermostat cycles on and off well below 24 hours a day even though it stays powered the whole time.
The examples on this page lean on continuous-duty equipment on purpose (a well pump, a space heater, a window air conditioner), because a single kW figure held steady across the whole run window is the case where this arithmetic is exact rather than approximate. A load that draws its rated power the entire time it runs needs nothing more than the hours it ran; a load that cycles or ramps needs an effective run-time figure instead, which the FAQ below walks through.
Where this total stops, and where the next page picks up
This calculator's job ends at the kWh figure itself. Turning that energy total into an actual dollar amount is a separate step: it needs a utility rate per kWh, and often a tiered or time-of-use rate structure on top of that, and belongs on the kilowatt-hour cost calculator, which multiplies a kWh total by a real rate to produce daily, monthly and annual cost figures. Keeping the two calculations apart makes it easier to check each one independently: get the energy total right first, then apply pricing.
Utilities bill by the kilowatt-hour, not the kilowatt, which is exactly why this conversion matters before cost ever enters the picture. A bill line item is always an energy total, never an instantaneous power reading.
The same formula runs in reverse too. If a plug-in meter reports a kWh total for a known number of run hours but the average power draw itself is unknown, dividing that kWh figure by the hours recovers the average kW. The swap button on the calculator above does exactly that: flip it and the same field pair solves kW = kWh ÷ hours instead of kWh = kW × hours.
Worked example: the well pump's daily and monthly total
4 kW well pump, running about 6 hours a day.
- 1
Apply the formula
kWh/day = 4 kW × 6 h
- 2
Solve for the daily total
4 × 6 = 24 kWh/day
- 3
Scale to a 30-day month
24 × 30 = 720 kWh/month
This is a planning estimate, not a metered reading: actual run time varies with well demand, weather and equipment condition, so treat the monthly figure as a reasonable projection rather than an exact bill amount.
Common continuous-duty equipment, kW to kWh/day
Typical running power and a representative run time for each load, applying kWh/day = kW × hours. The router and the fridge are listed at 24 hours because their kW figures are already an averaged effective draw across the whole day, including any off-cycles: the router as a near-constant load, the fridge as a typical cycling-compressor average. The rest reflect equipment that draws close to its full rated power for the whole listed run window. Actual run time varies by household, climate and equipment, use these as starting points, not measured values.
| Equipment | Running power | Typical run time | kWh/day |
|---|---|---|---|
| Wi-Fi router | 0.05 kW | 24 h/day | 1.2 kWh |
| Refrigerator (compressor running) | 0.15 kW | 24 h/day | 3.6 kWh |
| TV and electronics | 0.5 kW | 6 h/day | 3 kWh |
| Window AC unit | 1.2 kW | 8 h/day | 9.6 kWh |
| Space heater | 3 kW | 5 h/day | 15 kWh |
| Well pump | 4 kW | 6 h/day | 24 kWh |
| EV Level 2 charger | 7.2 kW | 4 h/day | 28.8 kWh |
Reference estimates only, not measured values. Confirm any real load against its own nameplate and actual run time.
From energy to what it costs
Questions
Kilowatts to kilowatt-hours FAQ
Run-time and duty-cycle questions that come up once a kW rating has to turn into a real energy total.
How do I estimate hours per day for equipment that doesn't run continuously, like a fridge?
Use the fraction of the day the compressor actually runs, not the fraction of the day the appliance is plugged in. A refrigerator is powered around the clock but its compressor cycles on and off. If a compressor draws 0.5 kW while running and its duty cycle is about 40% of each day, that is 9.6 hours of actual run time: 0.5 × 9.6 = 4.8 kWh/day. Guessing "24 hours" for a cycling load overstates the total by a wide margin.
Does a device's kW rating already account for its duty cycle?
No. A nameplate or spec-sheet kW figure is almost always the draw while the equipment is actively running, not an average smoothed across on and off periods. Multiplying that rating by 24 hours assumes constant operation, which is realistic for something like a well pump running its full duty window but wrong for a cycling load such as a fridge or a thermostatically controlled heater. Some energy-guide labels do list a pre-averaged annual kWh figure. That number already has the duty cycle baked in and should not be multiplied by run hours again.
How does this monthly estimate differ from what a smart meter actually reports?
This calculator projects a total from an assumed constant kW and a fixed hours-per-day figure, while a smart meter integrates real, moment-to-moment draw over the entire billing period. A meter captures startup surges, cycling, seasonal changes in run time and every other real-world variation this estimate holds constant. Treat the calculator's output as a planning figure to compare against a bill, not a substitute for the bill itself.
What changes if the load varies rather than staying constant through the run period?
Use the average kW over the run period, not the peak kW, or the kWh total will run high. An EV charger that tapers from 7.2 kW down to 3 kW as the battery fills, or a variable-speed motor that ramps up and down, does not draw its top rating for the whole session. Averaging the draw across the actual run time (or reading the session total directly off the charger or meter) gives a truer kWh figure than plugging in the nameplate maximum.
How do I turn a daily kWh estimate into a monthly figure?
Multiply the daily kWh total by the number of days in the billing period; 30 is a reasonable default when the exact cycle length is not known. The 4 kW well pump example above runs 24 kWh/day, so 24 × 30 = 720 kWh for a 30-day month. A billing cycle that runs 28 or 31 days will land a little above or below that figure, so treat it as an estimate rather than the exact number a utility will invoice.
Should I use the nameplate wattage or a measured value for this calculation?
A measured value from a plug-in power meter is more accurate than a nameplate rating for continuous-duty equipment, because nameplates are commonly stamped with a maximum or worst-case draw rather than typical running power. A well pump, sump pump or space heater can draw noticeably less than its nameplate figure once it settles into normal operation. When a measured reading is not available, the nameplate kW is still a reasonable starting point for a rough estimate; just expect the real total to run a bit lower.