The Quick Answer
To calculate how much it costs to run any electrical appliance:
Cost = (Watts ÷ 1,000) × Hours used × Rate per kWh
A 1,500W space heater running for 8 hours at $0.14/kWh costs:
(1,500 ÷ 1,000) × 8 × $0.14 = $1.68
That's the core formula. The rest of this article explains each piece, shows how to find the numbers you need, and covers the details that trip people up.
What Is a Kilowatt-Hour (kWh)?
A kilowatt-hour is a unit of energy. It represents using 1,000 watts of power for one hour.
- A 100W light bulb running for 10 hours uses 1 kWh (100 × 10 = 1,000 watt-hours = 1 kWh)
- A 2,000W hair dryer running for 15 minutes uses 0.5 kWh (2,000 × 0.25 hours = 500 Wh = 0.5 kWh)
- A 10W LED bulb running for 100 hours uses 1 kWh (10 × 100 = 1,000 Wh = 1 kWh)
Your utility company charges you per kWh consumed. That's the number on your bill.
Watts vs Kilowatt-Hours
These are frequently confused:
- Watts (W) measure the rate of energy use — how much power a device draws at any moment.
- Kilowatt-hours (kWh) measure the total energy consumed over time — how much power a device used over a period.
Think of it like speed vs distance. Watts are how fast you're using energy. Kilowatt-hours are how far you went.
The Electricity Cost Formula, Step by Step
Step 1: Find the Wattage
Check the appliance label, manual, or manufacturer's website. Wattage is usually printed on a sticker on the back or bottom of the device. Common notation: "120V ~ 1500W" or "1.5 kW."
If you can only find amps, multiply by voltage to get watts:
Watts = Volts × Amps
In the US, standard outlets are 120V. A device drawing 12.5 amps uses 120 × 12.5 = 1,500W.
For 240V appliances (dryers, ovens, AC units), use 240V in the calculation.
Step 2: Estimate Hours of Use
Be honest about how long the device actually runs — not how long it's plugged in. Many appliances cycle on and off:
- A refrigerator is plugged in 24/7 but its compressor runs roughly 8–12 hours per day
- An air conditioner may be "on" for 10 hours but the compressor cycles, running about 60–70% of the time
- A coffee maker takes about 10 minutes to brew, not an hour
For cycling appliances, estimate the active run time, not just the time the device is switched on.
Step 3: Find Your Electricity Rate
Your rate per kWh appears on your utility bill. In the US, average residential rates range from roughly $0.10 to $0.35 per kWh depending on state and utility:
| Region | Typical rate (2025) |
|---|---|
| Louisiana, Arkansas | $0.08–$0.10/kWh |
| Texas, Midwest | $0.11–$0.14/kWh |
| National average (US) | $0.13–$0.17/kWh |
| California | $0.22–$0.35/kWh |
| New England | $0.20–$0.30/kWh |
| Hawaii | $0.30–$0.45/kWh |
If your bill shows tiered or time-of-use rates, you'll have multiple rates — more on that below.
Step 4: Calculate
Cost per day = (Watts ÷ 1,000) × Hours per day × Rate
Multiply by 30 for monthly, 365 for annual.
Worked example — window AC unit:
- Wattage: 1,200W
- Usage: runs about 8 hours/day (compressor active time)
- Rate: $0.15/kWh
Daily cost: (1,200 ÷ 1,000) × 8 × $0.15 = $1.44/day Monthly cost: $1.44 × 30 = $43.20/month Summer cost (4 months): $43.20 × 4 = $172.80
What Common Appliances Actually Cost to Run
These estimates use a rate of $0.14/kWh. Your costs will be proportionally higher or lower based on your local rate.
High-cost appliances
| Appliance | Typical wattage | Daily use | Daily cost | Monthly cost |
|---|---|---|---|---|
| Central AC | 3,000–5,000W | 6–8 hrs | $2.52–$5.60 | $76–$168 |
| Space heater | 1,500W | 8 hrs | $1.68 | $50 |
| Electric water heater | 4,500W | 3 hrs | $1.89 | $57 |
| Clothes dryer | 5,000W | 1 hr | $0.70 | $21 (3×/wk) |
| Electric oven | 2,500W | 1 hr | $0.35 | $11 |
Medium-cost appliances
| Appliance | Typical wattage | Daily use | Daily cost | Monthly cost |
|---|---|---|---|---|
| Dishwasher | 1,800W | 1 hr | $0.25 | $8 |
| Washing machine | 500W | 1 hr | $0.07 | $2 (3×/wk) |
| Desktop computer | 200–400W | 6 hrs | $0.17–$0.34 | $5–$10 |
| Gaming console | 100–200W | 3 hrs | $0.04–$0.08 | $1–$3 |
| Refrigerator | 150W avg | 24 hrs* | $0.50 | $15 |
*Refrigerator compressor cycles — 150W is the average effective draw.
Low-cost appliances
| Appliance | Typical wattage | Daily use | Daily cost | Monthly cost |
|---|---|---|---|---|
| LED bulb | 10W | 8 hrs | $0.01 | $0.34 |
| Phone charger | 5–20W | 2 hrs | <$0.01 | $0.08 |
| Wi-Fi router | 10–20W | 24 hrs | $0.03–$0.07 | $1–$2 |
| Ceiling fan | 30–75W | 8 hrs | $0.03–$0.08 | $1–$3 |
| Laptop | 50–65W | 6 hrs | $0.04–$0.05 | $1.30–$1.60 |
The pattern is clear: heating and cooling dominate electricity bills. Devices that generate heat — space heaters, water heaters, dryers, ovens — draw the most power. Devices that process information or move air use comparatively little.
How to Read Your Electricity Bill
Utility bills can be confusing. Here are the key numbers to look for:
Total kWh used
This is your actual energy consumption for the billing period. A typical US household uses 800–1,000 kWh/month, but this varies widely by climate, home size, and habits.
Rate per kWh
The price you pay per kilowatt-hour. Look for "energy charge" or "supply charge." This is the number to plug into the electricity cost formula.
Delivery charges
Many utilities split bills into two parts: supply (the cost of generating electricity) and delivery (the cost of transmitting it to your home). Both are per-kWh charges. For an accurate rate calculation, add them together:
Effective rate = Supply rate + Delivery rate
If your supply charge is $0.08/kWh and delivery is $0.06/kWh, your effective rate is $0.14/kWh.
Fixed charges
Most bills include a flat monthly service fee ($5–$15 typically) regardless of usage. This covers infrastructure maintenance and metering. It's not affected by how much electricity you use.
Tiered pricing
Some utilities charge more per kWh as you use more:
- First 500 kWh: $0.12/kWh
- 501–1,000 kWh: $0.16/kWh
- Over 1,000 kWh: $0.22/kWh
With tiered pricing, reducing usage at the top tier saves the most money per kWh eliminated.
Time-of-use (TOU) pricing
TOU plans charge different rates at different times:
- Off-peak (typically 9 PM – 7 AM): lowest rate
- Mid-peak (morning and evening shoulders): moderate rate
- On-peak (afternoon, typically 2 PM – 7 PM): highest rate
The difference can be significant — on-peak rates might be 2–3× the off-peak rate. If you're on a TOU plan, shifting heavy loads (EV charging, laundry, dishwasher) to off-peak hours can cut costs meaningfully.
Standby Power: The Hidden Cost
Many devices draw power even when "off." This phantom load — also called standby power or vampire draw — happens with anything that has a standby light, remote control, clock, or network connection.
Typical standby draws:
| Device | Standby wattage |
|---|---|
| Cable box / DVR | 15–40W |
| Game console (standby) | 5–15W |
| Smart TV (off) | 1–5W |
| Microwave (clock display) | 2–4W |
| Charger (no device attached) | 0.1–0.5W |
The US Department of Energy estimates standby power accounts for 5–10% of residential electricity use. A cable box drawing 25W continuously costs about $31/year at $0.14/kWh — and it's doing nothing useful most of that time.
Practical fix: Use a smart power strip or simply unplug devices you don't use daily.
Electricity for Electric Vehicles
EV charging is a growing part of household electricity bills. The math is straightforward:
Charging cost = Battery capacity (kWh) × Rate per kWh
A typical EV with a 60 kWh battery charged from 20% to 80% (48 kWh used):
48 × $0.14 = $6.72 for roughly 180 miles of range.
That works out to about $0.037 per mile — significantly less than gasoline for most vehicles. At off-peak TOU rates ($0.08/kWh), the same charge costs $3.84, or about $0.021 per mile.
Level 2 home chargers (240V) draw 7–11 kW and typically charge overnight. Level 1 chargers (120V standard outlet) draw about 1.4 kW — slow, but workable for short daily commutes.
How to Reduce Electricity Costs
These are ordered by typical impact, highest first:
1. Address heating and cooling efficiency
HVAC is 40–50% of most electricity bills. Each degree you adjust your thermostat toward the outdoor temperature saves roughly 3% on heating/cooling costs.
2. Switch to LED lighting
LED bulbs use 75% less energy than incandescent bulbs and last 15–25 times longer. Replacing ten 60W incandescent bulbs with 10W LEDs saves about 500W of demand, or roughly $20/month if they run 8 hours daily.
3. Use timers and smart controls
Automating when devices run — lights, water heaters, pool pumps — can cut usage without changing behavior. A water heater timer that shuts off heating during overnight hours when no hot water is needed can save 5–10% of water heating costs.
4. Shift loads to off-peak hours
If your utility offers time-of-use rates, running the dishwasher, laundry, and EV charger during off-peak hours can reduce costs by 20–40% on those loads.
5. Eliminate standby loads
Use smart power strips for entertainment centers and home offices. $50 in smart strips can save $50–$100/year in standby power.
6. Maintain your refrigerator
Clean condenser coils annually. Make sure door seals are tight (the dollar-bill test: close the door on a bill — if it slides out easily, the seal needs replacing). A well-maintained fridge uses 15–20% less energy than a neglected one.
7. Use a kill-a-watt meter
If you're serious about finding waste, plug a watt meter (about $25) between devices and the wall. Measure actual consumption for 24 hours — you'll likely find surprises.
Solar and Net Metering: A Brief Note
If you have solar panels, your electricity math changes. With net metering, excess solar energy is credited against your bill — sometimes at the retail rate, sometimes at a lower wholesale rate, depending on your utility and jurisdiction.
The cost formula still applies: you're simply reducing the kWh you buy from the grid, or getting credited for kWh you send back. The economics depend heavily on local policies, solar exposure, and system size.
FAQ
How do I calculate the electricity cost of an appliance?
Use the formula: (Watts ÷ 1,000) × Hours used × Rate per kWh. For example, a 1,000W microwave running 15 minutes daily at $0.14/kWh costs (1,000 ÷ 1,000) × 0.25 × $0.14 = $0.035/day or about $1.05/month.
What is a kWh?
A kilowatt-hour (kWh) is a unit of energy equal to using 1,000 watts for one hour. It's the standard unit on electricity bills. One kWh can power a 100W bulb for 10 hours, a 2,000W heater for 30 minutes, or a 10W LED for 100 hours.
How much does electricity cost per kWh?
The US national average is approximately $0.13–$0.17/kWh for residential customers. Rates vary by state — from around $0.08/kWh in some Southern states to over $0.30/kWh in Hawaii and parts of New England and California. Check your utility bill for your exact rate.
How much does it cost to run a space heater?
A standard 1,500W space heater at $0.14/kWh costs about $0.21/hour, $1.68 for 8 hours, or approximately $50/month if used 8 hours daily. Space heaters are among the most expensive appliances to operate due to their high wattage and long run times.
How much electricity does a TV use?
A modern LED TV (55-inch) uses about 60–80W while on. At $0.14/kWh, running it 5 hours daily costs about $0.04–$0.06/day or $1.30–$1.70/month. Older plasma TVs used 200–400W and cost 3–5× more.
Does turning lights off save money?
Yes, but the amount depends on the bulb type. Turning off a 60W incandescent bulb for one hour saves $0.0084 at $0.14/kWh. Turning off a 10W LED saves $0.0014. Over a year, the habit matters more for rooms with multiple lights left on for hours.
Is it cheaper to run a dishwasher or wash by hand?
A modern dishwasher typically uses less water and roughly the same energy as hand-washing for a full load. Energy Star-rated dishwashers use about 1.5 kWh per cycle, costing about $0.21. Hand-washing uses more hot water, which costs more to heat. Run the dishwasher with full loads for best efficiency.
How much does it cost to charge a phone?
Very little. A phone battery holds about 15–20 Wh. Charging once daily at $0.14/kWh costs about $0.003/day — roughly $1 per year. Phone charging is one of the least significant electricity costs.
What uses the most electricity in a home?
In most homes: (1) Air conditioning and heating — 40–50% of the bill, (2) Water heating — 14–18%, (3) Refrigerator — 4–8%, (4) Clothes dryer — 4–6%, (5) Lighting — 4–6%. The split varies by climate, household size, and equipment age.
How do I find the wattage of an appliance?
Check the label on the back or bottom of the device, the owner's manual, or the manufacturer's website. If only amps are listed, multiply by voltage (120V for standard US outlets, 240V for large appliances) to get watts.
What is standby power and how much does it cost?
Standby power (vampire load) is electricity drawn by devices that are "off" but still plugged in. The US average is 5–10% of residential electricity, costing $100–$200/year per household. Cable boxes, game consoles, and smart TVs are common offenders.
Is it cheaper to run appliances at night?
Only if your utility offers time-of-use (TOU) pricing. With TOU plans, off-peak rates (typically overnight) can be 30–50% lower than peak rates. If you're on a flat rate, it makes no difference when you run appliances.
How much does it cost to run a pool pump?
A typical pool pump draws 1,500–2,500W and runs 6–8 hours daily. At $0.14/kWh, that's $1.26–$2.80/day or $38–$84/month. Variable-speed pumps running at lower speeds can cut this cost by 50–70%.
How do I calculate my total electricity rate from my bill?
Divide total electricity charges (supply + delivery, excluding fixed fees) by total kWh used. Example: if your charges are $140 for 1,000 kWh, your effective rate is $0.14/kWh. Include both supply and delivery components for accuracy.
Does a bigger fridge use more electricity?
Generally yes, but efficiency matters more than size. A new 25-cubic-foot Energy Star fridge may use 500 kWh/year, while an old 18-cubic-foot model from the 1990s might use 800 kWh/year. Age and efficiency rating have a larger impact than physical size.
Try It Yourself
Use the electricity cost calculator to estimate costs for any appliance — enter the wattage, daily usage hours, and your electricity rate to see daily, monthly, and annual costs instantly. You can also use the energy unit converter to convert between joules, kWh, and other energy units.