LED lighting cost calculator
Work out how much it costs to run a set of LED bulbs — a room, a whole house, or an outdoor lighting run — from their wattage, count and daily use.
Result
Cost per year
Cost per week
How to use this tool
- Check the power rating of the LED bulbs you're using, in watts.
- Enter how many bulbs and how many hours a day they're switched on.
- Enter your electricity price per kWh.
- Read the estimated cost per week and per year.
Assumptions
- Assumes all bulbs run for the same number of hours per day — for a mixed set (some rooms used more than others), run this separately per group.
Technical details: what the fields mean
- Power per bulb
powerWattsPerBulb - Power rating of the specific bulb from its label; the prefilled wattage is illustrative.
- Number of bulbs
bulbCount - How many bulbs are covered by this calculation, e.g. all the bulbs in one room.
- Hours on per day
hoursPerDay - How many hours a day the bulbs are typically switched on.
- Electricity price
pricePerKwh - Your electricity price per kWh.
Methodology
Total power = power per bulb × bulb count. Energy per week = total power (kW) × hours per day × 7. Cost = energy × price per kWh, projected to a year.
Worked example
5 bulbs at 8W each, 5 hours/day, entered rate £0.27/kWh
Inputs: Power per bulb: 8 W, Number of bulbs: 5, Hours on per day: 5 hours, Electricity price: £0.27/kWh
Result: 40W total × 5 hours = 0.2 kWh/day, about £0.05/day; £0.38/week and £19.76/year if repeated every day for 52 weeks.
Practical guidance
- For a brightness comparison, compare the bulbs' lumen ratings as well as watts; this tool estimates cost from the wattage and hours entered.
- Run separate estimates for groups of lights with different wattages or daily schedules.
Common mistakes
- Comparing an LED bulb's wattage directly to an old incandescent or halogen bulb's wattage as if they gave the same brightness — check the lumens rating instead for a fair comparison.
FAQs
Can I compare bulbs by wattage alone?
No. Watts measure power use; compare lumens for light output, then use each bulb's rated watts here to calculate running cost.
Last reviewed: 2026-10-11
A straightforward power × time estimate for a uniform set of bulbs — mixed bulb types or usage patterns need separate calculations per group.
This tool provides an indicative estimate, based on the assumptions stated above.
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