How to Calculate Appliance Running Cost
Quick formula
- Daily cost:
(watts × hours/day ÷ 1000) × $/kWh - Monthly cost: multiply daily cost by 30
- Annual cost: multiply daily cost by 365
- Example: 1500 W heater, 4 h/day, $0.16/kWh → (1500 × 4 ÷ 1000) × 0.16 = $0.96/day → $28.80/month
Use the Electricity Cost Calculator to run this math instantly.
The three numbers you need
To calculate running cost you need: (1) wattage, (2) hours of use, and (3) your electricity rate.
Wattage: Found on the appliance nameplate, in the manual, or by measuring with a plug-in energy monitor. If the nameplate shows amps and volts rather than watts, multiply them: W = A × V. See How to Find Appliance Wattage for more.
Hours of use: How long does the device actually run each day? Be realistic, a space heater set to "auto" may only heat for 2 of the 8 hours you have it on. A refrigerator runs its compressor intermittently, not constantly.
Electricity rate: Found on your electric bill, usually listed as cents per kWh. Divide the "energy charge" line item by the total kWh used for your effective rate. See How to Read Your Electric Bill.
The formula in full
Cost = (W × h ÷ 1000) × rate
Step by step:
- Multiply watts by daily hours to get watt-hours:
W × h - Divide by 1000 to convert to kWh:
÷ 1000 - Multiply by your rate in $/kWh to get the daily cost.
- Multiply by 30 for monthly, or 365 for annual.
Worked examples
Example 1: Space heater
A 1500 W space heater runs 4 hours per day. Rate: $0.16/kWh.
kWh/day = (1500 × 4) ÷ 1000 = 6 kWh
Cost/day = 6 × $0.16 = $0.96
Cost/month = $0.96 × 30 = $28.80
Running a space heater 4 hours a day all month adds nearly $29 to your bill, which is why they show up so clearly in winter electric bills.
Example 2: Refrigerator
A refrigerator draws 150 W on average (compressor cycles on and off). Rate: $0.16/kWh.
kWh/day = (150 × 24) ÷ 1000 = 3.6 kWh
Cost/month = 3.6 × 30 × $0.16 = $17.28
The refrigerator never turns off, it runs 24/7. Even at low wattage, that adds up to a meaningful baseline on your bill.
Example 3: Electric dryer
A 5500 W electric dryer runs 1 hour per cycle, 5 cycles per week. Rate: $0.16/kWh.
kWh/cycle = (5500 × 1) ÷ 1000 = 5.5 kWh
Cost/week = 5.5 × 5 × $0.16 = $4.40
Cost/month = $4.40 × 4.3 ≈ $18.92
Reference table: estimated monthly cost at $0.16/kWh
| Appliance | Wattage | Daily use assumed | Monthly cost (est.) |
|---|---|---|---|
| LED bulb (10 W) | 10 W | 6 h | ~$0.29 |
| Phone charger | 20 W | 2 h | ~$0.19 |
| Laptop | 65 W | 8 h | ~$2.50 |
| TV (50") | 100 W | 5 h | ~$2.40 |
| Refrigerator | 150 W avg | 24 h | ~$17.28 |
| Dishwasher | 1200 W | 1 h | ~$5.76 |
| Space heater | 1500 W | 4 h | ~$28.80 |
| Electric dryer | 5500 W | ~1 h (5×/wk) | ~$18.92 |
Adjust hours and rate for your actual usage. These are illustrative estimates, real cost depends on actual runtime and your local rate.
The difference between nameplate wattage and actual draw
Many appliances do not run at full nameplate wattage the whole time they are "on." A refrigerator compressor cycles; a space heater with a thermostat cuts out when the room reaches temperature; a dishwasher heats and then holds. To get an accurate monthly cost estimate, you need the actual average draw, not the nameplate peak.
The best tool for this is a plug-in energy monitor: it measures cumulative kWh over hours or days, giving you the real number. For planning purposes, nameplate wattage gives a conservative (slightly high) estimate, which is fine for budgeting.
Related tools and guides
- Electricity Cost Calculator, calculate running cost instantly
- kWh Calculator, just energy use without the cost
- How to Find Appliance Wattage
- How to Read Your Electric Bill
- Standby Power: Vampire Loads Explained
- Electricity Basics: Voltage, Current, and Resistance
FAQ
What electricity rate should I use?
Find your rate on your electric bill; look for a line that says "energy charge" and a per-kWh dollar amount. Divide the energy charge by kWh used to get your effective blended rate. The US average in 2025 is around $0.16/kWh, but rates range from $0.09 to over $0.30 depending on location.
How do I account for appliances that cycle on and off?
Use the average wattage, not the peak. A refrigerator that draws 300 W when the compressor is running but cycles 50% of the time has an average draw of 150 W. A plug-in energy monitor will give you the actual average automatically. Alternatively, use the annual kWh from the EnergyGuide label (divide by 8760 to get average watts).
Can I use this formula for my whole home?
You can, but it gets complicated because you would need to account for every device and its actual duty cycle. An easier approach: compare your utility bill's kWh to the formula results for your major appliances. If the major appliances account for most of the bill, your math is roughly right. If there is a big gap, you have loads you haven't accounted for.
My bill is much higher than the formula predicts. Why?
Common reasons: you underestimated hours of use, a device draws more than its nameplate (especially microwaves and devices with reactive loads), your rate is higher than you assumed, or there are standby loads you have not measured. Try a plug-in monitor on your highest-draw appliances to verify actual draw versus nameplate.
Is it worth calculating cost for small devices?
For very low-wattage devices (under 20 W), the monthly cost is usually under $0.50. This is worth knowing for completeness, but the time you spend calculating is worth more than the savings from turning them off. Focus your energy-saving efforts on the high-wattage devices that run for hours daily, space heaters, water heaters, HVAC, and refrigerators, where even small improvements mean real dollars.
Disclaimer: Results are informational estimates for learning and planning only. Always follow the applicable electrical code and consult a qualified licensed electrician for safety-critical work.