How to Estimate Electricity Cost
Understanding your electricity bill starts with knowing how power consumption is measured. Whether you want to identify energy-hungry appliances or predict your monthly costs, the calculation is straightforward once you know the formula.
The Core Formula: Watts → kWh → Cost
Step 1 — Convert watts to kWh:
kWh = (Watts ÷ 1,000) × Hours used Step 2 — Calculate cost:
Cost = kWh × Price per kWh Every appliance has a wattage rating (W) that tells you how much power it draws. Dividing by 1,000 converts to kilowatts (kW). Multiply by hours of use to get kilowatt-hours (kWh) — the unit your utility company charges for.
Step-by-Step Guide
- Find the wattage. Check the label on the appliance, the owner's manual, or search the model number online. Appliances often show a range (e.g., 800–1200W) — use the average or measure with a smart plug for accuracy.
- Estimate daily usage hours. Think about how long you actually use each device per day. The refrigerator runs ~24 hours, but a washing machine might only run 1 hour every other day.
- Calculate daily kWh. Apply the formula: (Watts ÷ 1,000) × hours. A 150W TV watched 4 hours/day uses (150 ÷ 1000) × 4 = 0.6 kWh/day.
- Find your electricity rate. Your rate (price per kWh) is on your electricity bill, usually in the "rate" or "tariff" section. If you have time-of-use pricing, note your peak and off-peak rates.
- Multiply kWh by rate. 0.6 kWh × $0.15/kWh = $0.09/day. Multiply by 30 for monthly: $2.70/month for that TV.
- Sum all appliances. Repeat for every major device. Your total should roughly match your actual bill (within 10–15% is good, since billing includes standing charges and taxes).
Common Appliance Consumption
| Appliance | Typical Wattage | Avg. Daily Hours | Monthly kWh |
|---|---|---|---|
| Refrigerator | 150–400 W | 24 h | 108–288 kWh |
| Air conditioner (window) | 900–1,440 W | 8 h | 216–346 kWh |
| Electric water heater | 3,000–4,500 W | 3 h | 270–405 kWh |
| Clothes dryer | 4,000–6,000 W | 0.5 h | 60–90 kWh |
| Dishwasher | 1,200–2,400 W | 1 h | 36–72 kWh |
| Washing machine | 500–1,000 W | 1 h | 15–30 kWh |
| LED TV (55") | 60–120 W | 4 h | 7–14 kWh |
| Desktop computer | 150–300 W | 4 h | 18–36 kWh |
| Laptop | 20–50 W | 6 h | 4–9 kWh |
| LED bulb (9W) | 9 W | 5 h | 1.4 kWh |
| Microwave | 800–1,500 W | 0.25 h | 6–11 kWh |
| Electric oven | 2,000–5,000 W | 0.5 h | 30–75 kWh |
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Open Electricity Cost Calculator →Tips to Reduce Electricity Costs
- Switch to LED lighting. LEDs use 75% less energy than incandescent bulbs and last 25× longer. Replacing 10 bulbs can save $50–100/year.
- Lower your water heater temperature. Set it to 120°F (49°C) instead of 140°F. This alone can reduce water heating costs by 6–10%.
- Use a smart or programmable thermostat. Setting back the temperature by 7–10°F for 8 hours/day can save up to 10% on heating and cooling annually.
- Run full loads only. Washing machines and dishwashers use roughly the same energy whether half-full or full. Waiting for a full load halves the cost per use.
- Unplug standby electronics. TVs, game consoles, and chargers draw power even when "off." A power strip with a switch makes it easy to cut phantom loads — worth $50–100/year.
- Seal air leaks. Drafts around windows and doors force your HVAC to work harder. Weather stripping costs a few dollars and can reduce heating/cooling costs by 10–20%.
- Use off-peak tariffs. If your utility offers time-of-use pricing, run high-consumption appliances (dishwasher, dryer, EV charging) at night when rates are lower.
Frequently Asked Questions
How do I calculate the cost of running an appliance?
Use this formula: Cost = (Wattage ÷ 1000) × Hours used × Price per kWh. For example, a 100W light bulb running for 10 hours at $0.15/kWh costs (100 ÷ 1000) × 10 × $0.15 = $0.15. Scale this to monthly usage by multiplying daily cost × 30.
What is a kilowatt-hour (kWh)?
A kilowatt-hour is the standard unit of electricity billing. It equals 1,000 watts of power used for 1 hour. So a 1,000W microwave running for 1 hour uses exactly 1 kWh. Most households use 250–500 kWh per month.
How do I read my electricity meter?
Analog meters have a row of dials — read them left to right, noting the lower number when the pointer is between two digits. Digital meters show the reading directly. Subtract last month's reading from this month's to get your kWh consumption. Smart meters often have a display button to cycle through readings.
What uses the most electricity at home?
The biggest energy consumers in most homes are: electric water heater (3,000–4,500W), air conditioner or heat pump (1,500–5,000W), electric dryer (4,000–6,000W), refrigerator (150–400W running continuously), and dishwasher (1,200–2,400W per cycle). Heating and cooling typically account for 40–50% of an average electricity bill.
How can I lower my electricity bill?
The most effective strategies are: switch to LED lighting (saves up to 75% on lighting costs), set your water heater to 120°F/49°C, use a programmable thermostat, run dishwasher and washer only when full, unplug standby electronics (phantom load can add 5–10% to bills), and seal drafts around windows and doors.