Appliance Energy Calculator Formula
Understand the math behind the appliance energy calculator. Each variable explained with a worked example.
Formulas Used
Annual Cost
annual_cost = annual_kwh * rate_per_kwhMonthly Cost
monthly_cost = annual_kwh * rate_per_kwh / 12Annual Energy Use
annual_energy = annual_kwhDaily Energy Use
daily_kwh = wattage * hours_per_day / 1000Variables
| Variable | Description | Default |
|---|---|---|
wattage | Appliance Wattage(watts) | 1500 |
hours_per_day | Hours Used per Day(hours) | 3 |
days_per_year | Days Used per Year(days) | 365 |
rate_per_kwh | Electricity Rate(USD/kWh) | 0.15 |
annual_kwh | Derived value= wattage * hours_per_day * days_per_year / 1000 | calculated |
How It Works
How to Calculate Appliance Energy Cost
Every electrical appliance has a wattage rating that determines how much energy it uses.
Formula
Annual kWh = Wattage * Hours/Day * Days/Year / 1,000
Annual Cost = Annual kWh * Rate per kWh
Common Appliance Wattages
Worked Example
A 1,500W space heater used 3 hours/day for 365 days at $0.15/kWh.
- 01Annual kWh: 1,500 * 3 * 365 / 1,000 = 1,642.5 kWh
- 02Annual cost: 1,642.5 * $0.15 = $246.38
- 03Monthly cost: $246.38 / 12 = $20.53
- 04Daily kWh: 1,500 * 3 / 1,000 = 4.5 kWh
Frequently Asked Questions
Where do I find my appliance wattage?
Check the label on the appliance, the user manual, or the manufacturer website. Wattage is usually listed on a sticker near the power cord or on the bottom of the device.
Which appliances use the most electricity?
HVAC systems, water heaters, clothes dryers, and electric ovens are typically the largest energy consumers. Refrigerators use moderate power but run 24/7.
Does an appliance use energy when turned off?
Many appliances draw standby or phantom power when plugged in but off. TVs, gaming consoles, and chargers commonly draw 1-10 watts in standby mode.
Ready to run the numbers?
Open Appliance Energy Calculator