Use your tariff, not somebody else's headline
Electricity prices vary by country, tariff, payment method and date. A search result promising a fixed number of pence per hour may be wrong by the time you read it. Find the unit rate shown on your latest bill or supplier account and use that figure before tax treatment where appropriate to your bill.
The standing charge is paid regardless of whether the dehumidifier runs, so it is normally excluded when comparing the additional cost of using the appliance. If your tariff has different time bands, calculate each band separately.
The calculation in three steps
Convert watts to kilowatts by dividing by 1,000. Multiply kilowatts by hours to estimate kilowatt-hours, then multiply by your electricity price per kWh. For example, a 250 W appliance running continuously for four hours uses a maximum of 1.0 kWh: 0.25 × 4 = 1.0.
To turn that energy into money, multiply 1.0 kWh by the unit rate on your bill. We deliberately do not insert a current national rate because it would make the guide inaccurate for many readers and dates.
| Input | Calculation | Your figure |
|---|---|---|
| Rated or measured power | Watts ÷ 1,000 | ___ kW |
| Energy for the session | kW × hours | ___ kWh |
| Session cost | kWh × tariff unit price | ___ |
| Monthly estimate | Session cost × sessions | ___ |
Why the label wattage is only an estimate
A dehumidifier's compressor, heater and fan may not draw their full rated power continuously. A humidistat can stop moisture removal after the target is reached, while the fan may continue or cycle. Defrost, laundry and high-fan modes can produce different profiles.
This means rated watts multiplied by elapsed time is a useful upper-bound estimate, not necessarily measured consumption. A plug-in electricity monitor can record the complete session. Follow the monitor's electrical rating and safety instructions, and do not use an unsuitable smart plug in a damp location.
Measure cost per result
An hourly price can reward a slow machine simply because it draws less power each hour. Instead compare the energy needed to achieve the same useful result. For room control, record the kWh required to move from the same starting temperature and RH to the same target. For laundry, compare similar loads from the same washing-machine spin setting.
Record elapsed time too. The lowest-energy option may not be acceptable if it takes so long that laundry remains wet overnight or the room cannot be used. Cost, speed, noise and moisture control are separate outcomes.
- Use the same room, target RH and door/window position.
- Record starting and finishing temperature and humidity.
- Measure total kWh rather than reading instantaneous watts once.
- Repeat at least three comparable sessions before drawing a conclusion.
Capacity and efficiency are not the same
Headline litres per day describe extraction under test conditions. An efficiency metric describes water removed per unit of electricity under those conditions. A larger capacity machine can be more efficient than a smaller one, while a well-controlled larger unit may also reach the target sooner and cycle.
Only compare certified figures produced under the same standard. Real collection will change with room temperature and humidity, so use those ratings to create a shortlist rather than predict an exact household bill.
Ways to reduce waste without undermining moisture control
Set a reasonable humidity target instead of forcing continuous operation. Keep doors and windows in the position required by your plan; trying to dehumidify an open house is rarely efficient. Clean filters at the interval in the manual and keep inlet and outlet clear.
Reduce moisture at source with working extraction, covered cooking pans, externally vented dryers and prompt repair of leaks. For laundry, use the fastest suitable washing-machine spin and space garments so air can circulate. These measures reduce the load rather than asking the appliance to work longer.
Do not turn the unit off merely to produce a smaller bill if persistent condensation or damp remains. The correct comparison includes the cost of unresolved moisture and the need to address its cause.
Common questions
Questions this guide should answer
How do I calculate dehumidifier cost per hour?
Divide watts by 1,000 and multiply by the unit price per kWh on your electricity bill. This assumes continuous draw at that wattage, so measured consumption may differ.
Does a dehumidifier use full power all the time?
Not necessarily. Humidistat cycling, fan behaviour, defrost and operating mode can all change consumption. A suitable plug-level monitor provides a better session total.
Is a bigger dehumidifier more expensive to run?
Not automatically. It may draw more power while active but reach the target sooner. Compare total kWh for the same outcome.
Should the standing charge be included?
Usually not when estimating the additional cost of the appliance, because you pay the standing charge even when it is off. Use your bill's unit rate for incremental energy use.
Sources and review trail
We favour primary public guidance and link to the exact source so you can inspect it yourself.