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 calculator
- 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 a single LED bulb — typically 5–10W for a standard household bulb.
- 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, 5 hours/day, 27p/kWh
Inputs: powerWattsPerBulb=8, bulbCount=5, hoursPerDay=5, pricePerKwh=0.27
Result: £0.38/week, £19.76/year
Practical guidance
- LED bulbs typically use around 80–90% less energy than old incandescent bulbs for the same brightness, so switching over is one of the cheapest efficiency upgrades available.
- Smart plugs or timers on frequently-forgotten lights (outdoor, hallway) can meaningfully cut the 'hours per day' figure.
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
How much does it cost to run 5 LED bulbs?
At 8W each, 5 hours a day and 27p/kWh, about 38p a week — roughly £19.76 a year.
How much cheaper are LEDs than old bulbs?
LEDs typically use 80–90% less energy than incandescent bulbs for the same brightness.