How to Use This Calculator
Electricity costs are based on kilowatt-hours (kWh) consumed. To estimate your bill, multiply the power draw (in watts) by the hours of operation, then divide by 1,000 to convert to kWh. Multiply kWh by your local electricity rate (in dollars per kWh) to get the cost.
This calculator helps you understand how much power specific appliances consume and what they cost to run. Enter the power rating (in watts) from the appliance’s nameplate or specification, the hours per day or month it operates, and your local electricity rate. The calculator shows total kWh and estimated cost. Example: a 5-kW air conditioning unit running 8 hours per day at $0.12/kWh costs 5 × 8 × 30 ÷ 1,000 × $0.12 = $14.40 per month.
Use this for energy audits, cost estimates, and customer education. When a homeowner complains about high bills, you can show them exactly how much their heating system, hot water heater, or old refrigerator is costing. Many choose to upgrade when they see the numbers.
Formula
Energy Consumption (kWh): kWh = (watts × hours) / 1,000
Where:
- Watts is the device’s power rating (from the nameplate)
- Hours is the duration of operation (hourly, daily, monthly, or annual)
- 1,000 converts watt-hours to kilowatt-hours
Cost Estimation: Cost = kWh × rate per kWh
Where:
- Rate is your local electricity rate, typically $0.08–$0.18 per kWh (varies by region and utility)
Common appliance wattages:
- Incandescent light bulb (60W): ~60 watts
- LED light bulb (equivalent): ~9–12 watts
- Electric range: 3,000–5,500 watts
- Refrigerator: 150–800 watts (continuous, cycles on/off)
- Dishwasher: 1,800–2,400 watts
- Air conditioner (window): 3,500–5,500 watts
- Central AC (5-ton unit): 3,500–5,000 watts
- Electric water heater: 4,000–5,500 watts
- Space heater: 750–1,500 watts
- Dryer: 3,000–6,000 watts
When to Use This
Customer service calls. A homeowner’s electric bill jumped from $80 to $150 per month. You can help them identify the culprit by calculating power consumption for each major appliance. An old refrigerator running 24/7 at 600 watts costs about $52/month at $0.12/kWh. Upgrading to an ENERGY STAR model (400 watts) saves $10/month or $120/year.
Contractors use this for estimating loads on temporary power during construction, calculating backup generator runtime, and advising customers on the electrical impact of new HVAC systems, heat pumps, or charging equipment. You’re not giving financial advice; you’re showing facts that help customers make informed decisions.
Code References
- No direct NEC reference, but understanding power consumption is critical for NEC Article 220 (branch-circuit, feeder, and service calculations), which determines service size and load planning
- Energy Conservation Measures: While not code per se, ASHRAE and local energy codes increasingly encourage efficiency; understanding consumption helps clients comply with mandates
Frequently Asked Questions
What’s my local electricity rate?
Check your utility bill. It’s usually stated in cents per kWh (or $/kWh). Rates vary widely: rural areas in the West may be $0.08/kWh, while the Northeast and California average $0.14–$0.18/kWh. Some utilities charge tiered rates (cheaper for lower usage, more expensive at higher tiers). Use your average rate for a rough estimate.
Can I estimate the power rating if the nameplate is missing?
Not reliably. You can measure current with a clamp meter and multiply by voltage (watts = V × A), but that’s an active measurement, not a conservative estimate. For appliances, look up the model online. Never guess. Underestimating power draw leads to undersized circuits; overestimating wastes effort. Look it up.
Why does my refrigerator use less power than a space heater if it runs 24/7?
Refrigerators cycle. A compressor runs every few minutes to remove heat, then stops. Average continuous load is much less than peak wattage. A 600-watt refrigerator might run only 8 hours per day (the compressor cycles), so daily consumption is 600 × 8 ÷ 1,000 = 4.8 kWh. A 1,500-watt space heater running continuously for 4 hours uses 1,500 × 4 ÷ 1,000 = 6 kWh. Context matters.
How much does it cost to run a 100-watt light bulb for an hour?
100 watts × 1 hour ÷ 1,000 = 0.1 kWh. At $0.12/kWh, that’s $0.012 or 1.2 cents per hour. Running 24/7 for a month costs 0.1 × 24 × 30 × $0.12 = $8.64. LED bulbs at 12 watts cost less than $1.04/month—a huge savings.
Can I estimate my entire home’s monthly bill this way?
You can get a rough estimate by adding up all appliances’ estimated consumption, but it’s easier to look at your monthly utility bill and calculate average cost per kWh. Divide total bill by total kWh used that month. Then multiply by kWh to estimate future bills. This approach accounts for rate tiers, demand charges (for commercial accounts), and seasonal variations that simple appliance calculations miss.