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Energy Cost Calculator

Calculate electricity cost from wattage, daily usage hours, and your local utility rate per kWh — with daily, monthly, and annual breakdowns.

Appliance Tracker

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Daily Cost
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Monthly Estimate (30 Days)

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Annual Extrapolation
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Requires exactly 0 total kWh generated.
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What is Kilowatt-Hour Energy Consumption & Cost?

How electricity meters measure energy as kilowatt-hours (kWh), and the formula utilities use to translate your appliance's wattage and operating hours into a monthly dollar charge.

Mathematical Foundation

kWh Electricity Cost Formula
Costdaily=W×H1000×RCost_{daily} = \frac{W \times H}{1000} \times R
WW= Appliance rated power draw in Watts
HH= Daily operating hours
10001000= Unit conversion factor: 1 kilowatt = 1,000 watts
RR= Utility rate in dollars per kilowatt-hour (kWh)

Laws & Principles

  • Watts vs. Watt-Hours: A Watt (W) is a unit of instantaneous power (rate of energy flow), not energy itself. A Watt-Hour (Wh) is a unit of energy consumed over time. A 100W light bulb running for 10 hours consumes 1,000 Wh = 1 kWh. Utility bills charge per kWh of energy consumed, never per Watt.
  • Standby Power (Phantom Load): Most consumer electronics continue drawing power even when 'off'. A TV on standby consumes roughly 1-5 watts continuously. Across an entire house, phantom loads can account for 5-10% of total electricity bills. Devices with clocks, charging circuits, or remote sensors are the primary culprits.

Step-by-Step Example Walkthrough

" Estimating the annual cost of running a 1,500W space heater for 8 hours per day at $0.16/kWh. "

  1. Daily kWh: (1500W × 8h) ÷ 1000 = 12 kWh per day.
  2. Daily cost: 12 kWh × $0.16 = $1.92 per day.
  3. Monthly estimate (30 days): $1.92 × 30 = $57.60/month.
  4. Annual cost: $1.92 × 365 = $700.80/year.
Final Result: A space heater used 8 hours/day costs ~$57.60/month or ~$700/year at average US rates.

Quick Answer: How Do You Calculate Electricity Cost?

Multiply watts × hours used per day ÷ 1000 × rate per kWh. A 1,500W space heater running 8 hours/day at $0.13/kWh costs $1.56 per day or $46.80 per month. The ÷ 1000 converts watts to kilowatts because your utility bills in kilowatt-hours (kWh), not watt-hours.

Common Appliance Running Costs (@ $0.13/kWh)

Appliance Watts Hrs/Day $/Day $/Month
LED Bulb10W8$0.01$0.31
Laptop65W8$0.07$2.03
Window AC1,200W10$1.56$46.80
Space Heater1,500W8$1.56$46.80
EV Charger (L2)7,200W4$3.74$112.32
Mining Rig3,000W24$9.36$280.80

US average residential rate: $0.13/kWh. Rates vary from $0.08 (Louisiana) to $0.32 (Hawaii). Check your utility bill for your exact rate — it's usually on the first page under "rate" or "price per kWh."

Energy Cost Tips

Do This

  • ✓Use actual wattage, not rated wattage. A "1,500W" space heater draws 1,500W at max setting. On medium, it might draw 750W. Use a plug-in power meter ($15-25) to measure actual draw for accurate cost estimates.
  • ✓Check for tiered pricing. Many utilities charge more per kWh as you use more. The first 500 kWh might cost $0.10, but usage above 1,000 kWh could cost $0.18. Use your highest tier rate for new appliances.

Avoid This

  • ✗Don't ignore phantom loads. TVs, game consoles, and chargers draw 5-25W even when "off." A home with 20 phantom loads at 10W each wastes 200W × 24 hours = 4.8 kWh/day = $18.72/month. Use smart power strips to cut power completely.
  • ✗Don't confuse watts and watt-hours. Watts measure rate of energy use (like speed). Watt-hours measure total energy consumed (like distance). A 100W bulb running for 10 hours uses 1,000 Wh = 1 kWh. Your bill charges for kWh, not watts.

Frequently Asked Questions

What is a kilowatt-hour (kWh)?

A kilowatt-hour is 1,000 watts used for one hour. It's the standard billing unit for electricity worldwide. A 100-watt bulb running for 10 hours uses 1 kWh. A 2,000-watt dryer running for 30 minutes also uses 1 kWh. The average US household uses about 900 kWh per month.

Where do I find my electricity rate?

Check your monthly utility bill — the rate per kWh is usually on the first page. If you see a total charge and total kWh used, divide the charge by kWh to get your effective rate. Many utilities also publish rate schedules on their website. The US national average is roughly $0.13/kWh, but ranges from $0.08 in states like Louisiana to over $0.30 in Hawaii and parts of California.

How do I find the wattage of an appliance?

Check the label on the appliance (usually on the back or bottom). It lists watts (W) or amps (A) and volts (V). If only amps and volts are listed, multiply them: Watts = Amps × Volts. For example, a label reading "5A, 120V" means 600 watts. For the most accurate measurement, use a plug-in power meter like a Kill-A-Watt — it measures actual real-time power draw including cycling appliances like refrigerators that don't run continuously.

Does this calculator account for time-of-use rates?

This calculator uses a single flat rate. If your utility charges time-of-use (TOU) rates with peak/off-peak pricing, run the calculator twice — once with your peak rate for daytime hours and once with your off-peak rate for nighttime hours, then add the results. For example, a dishwasher running 1 hour on-peak at $0.22/kWh and an EV charging 6 hours off-peak at $0.08/kWh should be calculated separately.

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