# Electricity cost calculator

> Electricity cost of running an appliance per hour, day, month and year, from its wattage, hours of use and your price per kWh (unit).

Интерактивная версия: https://www.calcopenly.com/ru/science/electricity-cost-calculator
Тема: Научные калькуляторы

The calculator turns an appliance's power rating into energy and money. Energy per day is the power in kilowatts times the hours of use, in kilowatt-hours (kWh); the monthly figure multiplies that by the days used, the yearly one by 12 months, and each is priced at your tariff per kWh. A kWh is the "unit" counted on electricity bills.

People use it to compare appliances or to see what a heater or air conditioner adds to a bill. The default, a 1.5 kW heater running 4 hours a day for 30 days at 0.15 per kWh, uses 6 kWh a day and 180 kWh a month: 27.00 a month and 324.00 a year.

The rated wattage is a maximum. Fridges, air conditioners and heaters with thermostats cycle on and off, so their real use is lower, and tiered tariffs, standing charges and time-of-day rates change the final bill.

## Входные данные

- **Appliance power**
- **Hours used per day**
- **Days used per month**
- **Price per kWh (unit)**
- **Number of appliances**

## Результаты

- Cost per month — основной результат
- Cost per year
- Cost per day of use
- Cost per hour
- Energy per day of use (kWh)
- Energy per month (kWh)
- Energy per year (kWh)

## Формула

$$
E_{\text{day}} = \frac{P \times h \times n}{1000}\ \text{kWh},\quad \text{cost}_{\text{month}} = E_{\text{day}} \times d \times \text{tariff},\quad \text{cost}_{\text{year}} = 12 \times \text{cost}_{\text{month}}
$$

## Примеры с решением

### 1.5 kW heater, 4 h a day, 30 days at 0.15

- Appliance power: 1500 W
- Hours used per day: 4 h
- Days used per month: 30 days
- Price per kWh (unit): 0.15
- **Energy per day of use: 6 kWh**
- **Energy per month: 180 kWh**
- **Cost per month: 27.00**
- **Cost per year: 324.00**
- Источник проверки: DOE method: 1500 W × 4 h ÷ 1000 = 6 kWh/day; × 30 × 0.15 = 27.00; × 12 = 324.00

### 100 W bulb, 5 h a day at 0.12

- Appliance power: 100 W
- Hours used per day: 5 h
- Days used per month: 30 days
- Price per kWh (unit): 0.12
- **Energy per month: 15 kWh**
- **Cost per month: 1.80**
- Источник проверки: Python 3.8 decimal: 0.1 kW × 5 × 30 × 0.12

### Two 1 hp motors, 8 h on 22 working days at 0.20

- Appliance power: 1 hp
- Hours used per day: 8 h
- Days used per month: 22 days
- Price per kWh (unit): 0.20
- Number of appliances: 2
- **Energy per day of use: 11.9312 kWh**
- **Cost per month: 52.50**
- **Cost per year: 629.97**
- Источник проверки: Python 3.8 decimal: 2 × 745.69987 W × 8 h = 11.9312 kWh/day; × 22 × 0.20 = 52.4973

### Ten 9 W LED bulbs, 6 h a day at ₹8

- Appliance power: 9 W
- Hours used per day: 6 h
- Days used per month: 30 days
- Price per kWh (unit): 8
- Number of appliances: 10
- **Energy per month: 16.2 kWh**
- **Cost per month: 129.60**
- Источник проверки: Python 3.8 decimal: 10 × 9 W × 6 h × 30 = 16.2 kWh; × 8 = 129.60

### Unused appliance costs nothing

- Appliance power: 2000 W
- Hours used per day: 0 h
- Days used per month: 30 days
- Price per kWh (unit): 0.15
- **Cost per month: 0.00**
- **Cost per year: 0.00**
- Источник проверки: 0 hours of use ⇒ 0 kWh (definition)

## Вопросы

### How do I calculate the cost of running an appliance?

Multiply the power in kilowatts by the hours of use to get kilowatt-hours, then multiply by the price per kWh. A 2,000 W (2 kW) heater used for 3 hours uses 6 kWh; at 0.15 per kWh that costs 0.90. The US Department of Energy gives the same method: watts × hours used per day ÷ 1,000 = daily kWh.

### What is a unit of electricity?

One unit is one kilowatt-hour (kWh): 1,000 watts used for one hour, which is 3.6 megajoules of energy. A 100 W bulb takes 10 hours to use one unit and a 2 kW kettle takes 30 minutes. Bills in the UK, India and many other countries count units, and the price per unit is the tariff to enter here.

### How do I find an appliance's wattage?

Look for the rating label on the back or base of the appliance, or in its manual; it lists watts or kilowatts. If it gives only amps, multiply by the supply voltage, as the US Department of Energy suggests: 5 A at 230 V is 1,150 W. A plug-in energy meter measures real consumption, including standby power and thermostat cycling.

### How much electricity does a fridge use?

Less than its rating suggests, because the compressor switches on and off. The US Department of Energy suggests dividing the hours a fridge is plugged in by three to estimate its full-power running time, so a 150 W fridge runs about 8 hours a day: 1.2 kWh a day, or 36 kWh in a 30-day month. The kWh-per-year figure on its energy label is a better guide when you have it.

### Насколько точен «Electricity cost calculator»?

Точность зависит от введённых данных и допущений метода. Десятичная арифметика использует 50 значащих цифр, но оценки, численные методы и исходные данные могут быть менее точными; округление на экране не устраняет эти ограничения. Решённые примеры, проверенные по независимым источникам: 5. Например, «1.5 kW heater, 4 h a day, 30 days at 0.15» проверяется по источнику DOE method: 1500 W × 4 h ÷ 1000 = 6 kWh/day; × 30 × 0.15 = 27.00; × 12 = 324.00.

### Откуда взята методика?

U.S. Department of Energy — Estimating appliance and home electronic energy use; BIPM SI Brochure (9th ed.), Table 8 — the kilowatt-hour is 3.6 MJ.

## Источники

- [U.S. Department of Energy — Estimating appliance and home electronic energy use](https://www.energy.gov/energysaver/estimating-appliance-and-home-electronic-energy-use)
- BIPM SI Brochure (9th ed.), Table 8 — the kilowatt-hour is 3.6 MJ