Discover how to accurately calculate the energy consumption and cost of your lighting, using only your monthly power bill and a simple calculator.

Things Needed

• Monthly electric bill
• Calculator or spreadsheet

Most utilities charge a higher rate for electricity used during peak periods. By breaking down your lighting usage, you can identify where savings are possible.

Step 1 – Determine the price per kilowatt‑hour

Divide your total monthly bill by the total kilowatt‑hours (kWh) shown on the bill. For example:

• Total bill = $150.00 • Total kWh = 1,060 • Cost per kWh = $150.00 / 1,060 = $0.1415 per kWh

Step 2 – Calculate a single bulb’s kWh usage

Take a 60 W bulb that runs 9 hours a day for a 30‑day month:

9 hrs × 30 days = 270 hrs 270 hrs × 60 W = 16,200 Wh 16,200 Wh / 1,000 = 16.2 kWh per month

Step 3 – Compute the cost for that bulb

16.2 kWh × $0.1415 = $2.29 (rounded) – the monthly cost of that single bulb.

Step 4 – Scale up to fixtures or entire rooms

If a fixture contains multiple bulbs, multiply the wattage by the number of bulbs, then repeat Steps 2 and 3. For example, a fixture with five 60 W bulbs totals 300 W:

300 W × 270 hrs = 81,000 Wh / 1,000 = 81 kWh 81 kWh × $0.1415 = $11.46 per month.

Repeat this process for every lighting installation to get a comprehensive picture of your lighting expenses.