Home & DIY
How many Christmas lights do you need?
Bulbs from tree height or metres of run, the metres to buy from your own string, and what the season costs to run.
Quick answer
Count bulbs, not metres. Metres are a property of the string, not of the tree: two 20 m strings can hold 200 or 400 bulbs, so the length on the box only tells you how far it reaches. For a 180 cm tree a normal look is about 430 bulbs; sparse is 270 and dense is 590, which is the old rule of 100 bulbs per foot of tree. Divide your bulb count by the bulbs-per-metre printed on the box and you get the metres you actually need to buy.
Bulbs you need
430
- Metres of string to buy
- 43 m
- Power
- 26 W
- Cost for the whole season
- 1.55 (6 kWh)
Metres are a property of the string, not of the tree: two 20 m strings can hold 200 or 400 bulbs. Read the bulbs-per-metre off the box and the length follows.
Bulb counts are a band, not a rule — sparse to dense is taste, and the dense end is the old guideline of 100 bulbs per foot of tree. Power assumes about 0.06 W per LED and 0.4 W per old incandescent bulb, which is roughly seven times more; your box may differ, and if it prints watts use that. ⛔ Nothing here is a safety rating: check the string is rated for outdoors before it goes outdoors.
How it works
| Tree height | Sparse | Normal | Dense |
|---|---|---|---|
| 120 cm | 180 | 290 | 390 |
| 150 cm | 230 | 360 | 490 |
| 180 cm | 270 | 430 | 590 |
| 210 cm | 320 | 500 | 690 |
| 240 cm | 360 | 580 | 790 |
| 270 cm | 410 | 650 | 890 |
The consumption question has two opposite answers, and that is the useful part. On a tree, with LEDs, the whole season costs about 1.55 — six hours a day for forty days. Stop worrying and leave them on. On a shop window with old bulbs left burning overnight it is about 288, and there the lever is not the LED swap: it is the timer. Cutting from 24 hours to 10 saves more than changing every bulb — the same window drops to about 120, and a timer costs less than one string.
| Case | Power | Season | At 0.25 per kWh |
|---|---|---|---|
| Tree 180 cm, LED | 26 W | 6 kWh | 1.55 |
| Tree 180 cm, old bulbs | 172 W | 41 kWh | 10.32 |
| House front, 10 LED strings | 60 W | 14 kWh | 3.60 |
| Shop window, 20 LED strings, 14 h | 120 W | 101 kWh | 25.20 |
| Shop window, 20 old strings, 14 h | 800 W | 672 kWh | 168.00 |
| Shop window, old bulbs, 24 h | 800 W | 1152 kWh | 288.00 |
Two things the bulb count will not tell you. A string is rated for a number of strings you may join end to end — usually printed next to the plug, often three or four — and going past it is the one genuinely dangerous mistake on this page; use a second socket instead. And outdoor rating is not a detail: an indoor string on a gutter survives until the first wet night. Neither of those is a number you can calculate, which is why they are written here rather than in the result.
Frequently asked questions
How many lights for a 180 cm Christmas tree?+
About 430 bulbs for a normal look — 270 if you want the tree itself to show through, 590 for the dense, shop-window effect. Those come from roughly 150, 240 and 330 bulbs per metre of tree, and the dense figure is the old guideline of 100 bulbs per foot. Then turn bulbs into metres using your own string: at 10 bulbs per metre, 430 bulbs is 43 m.
How much do Christmas lights cost to run?+
On a tree with LEDs, almost nothing: about 1.55 for the whole season at six hours a day for forty days. The number only becomes real in two cases. Old incandescent bulbs draw about seven times more, so the same tree costs around 10 instead. And a shop window with twenty old strings left on overnight reaches about 288 for the season — which is the case worth doing something about.
How many metres of lights do I need?+
That question has no answer until you pick the string. Metres belong to the product, not to the tree: a 20 m string can carry 200 bulbs or 400, and the same tree needs the same bulbs either way. Work out the bulbs first, read the bulbs-per-metre off the box, and divide. If the box only prints a length and a bulb count, divide those two and you have it.
Is it cheaper to replace old lights with LED, or to use a timer?+
On a tree, neither is worth doing for the electricity — you are arguing over a few euros a season. On a shop window the timer wins, and it is not close: going from 24 hours to 10 takes the same window from about 288 to about 120, which is more than the LED swap saves and costs the price of one plug. Do the timer first, then replace the strings when they break.
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