Energy Consumption Calculator
Work out energy use in kWh from power, hours per day and days. Formula, worked example and a table of typical values.
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Estimate only. Not engineering or safety advice. Check the result against the applicable standard and the equipment data, and have a competent engineer review it before it is relied on. Terms of use.
Open in the calculator with these values
Formula
Worked example
| Input | Value |
|---|---|
| Load | 2 kW |
| Run at (% of the load) | 100 |
| Hours of use | 8 |
| Hours of use are per | Day |
| Days to total | 30 |
| Tariff per kWh | 8 |
| Currency symbol on the results | None |
- Power drawn = 2 kW = 2 kW
- Hours per day = 8 h
- E per day = 2 kW × 8 h = 16 kWh; per month 486.67 kWh; per year 5,840 kWh
- Cost per day = 16 kWh × 8 = 128; per month 3,893.33; per year 46,720
- Over 30 days: E = 480 kWh, cost = 3,840
Typical values
| Load (kW) | Energy (days entered) (kWh) |
|---|---|
| 0.1 | 24 |
| 0.5 | 120 |
| 1 | 240 |
| 2 | 480 |
| 5 | 1,200 |
Other inputs are the same as in the worked example above.
Assumptions
- Constant draw at the run-at percentage while on
- Hours per week are spread over 7 days and hours per month over 365 / 12 = 30.42 days
- Flat tariff, no demand charges
- Typical appliance wattages are indicative, not measured values
This is the cost of one load at one flat rate. A real bill adds demand and fixed charges that are not modelled here. The per-month figure uses an average month of 30.42 days, so it differs a little from the days-to-total result when that is 30. For a whole bill from the units on your meter, with tariff slabs, a fixed charge and tax, use Electricity Bill from Tariff Slabs. Power can be entered in BTU/h (1 BTU/h = 0.29307 W) or tons of refrigeration (1 TR = 12,000 BTU/h = 3,516.85 W); that is the cooling rating, so check the electrical input power of an air conditioner on its label.
Frequently asked questions
How is Energy Consumption calculated?
E per day = P × (run-at % / 100) × hours per day; per month = × 365 / 12; per year = × 365; Cost = E × tariff. Worked example: Load 2 kW, run at (% of the load) 100, hours of use 8, hours of use are per Day gives 480 kWh.
What do I need to enter?
Enter load, run at (% of the load), hours of use, hours of use are per, days to total, tariff per kWh and currency symbol on the results. Change the unit of a value with its selector and the result stays the same.
How do I turn this into a cost?
Multiply the energy in kWh by your tariff per kWh. The Energy Cost calculator does this step for you.
Is this my whole electricity bill?
No. It is the energy and cost of one appliance or load at one flat rate. Your bill covers everything on the meter and often has slabs, a fixed charge and tax; use the Electricity Bill calculator for that.
How accurate are the results?
Every figure comes from the same tested engine as the Elecmetric calculators and is meant for estimating. Check design values against the standard and the equipment data you work to.
Related
Next steps in a design: Electricity Bill (tariff slabs)kW to kWhkW to Amps
Also see: Energy Cost (one appliance)
Formula guides: Energy and Cost Formulas: kWh and PaybackEnergy Meter Multiplier Formulas
Whole bill with slabs and tax: Electricity Bill (tariff slabs)
All 78 conversionsAppliance Running Cost (Energy and Cost) in Elecmetric