Christmas Lights Calculator
Estimate how many lights you need for a tree or garland based on its height/length and a lights-per-foot density. The default of 100 lights per foot is a commonly used decorating guideline — increase it for a denser look or decrease it for a sparser one.
How the light count is worked out
Two multiplications, each rounded up to a whole unit:
total lights = ceil(height or length in ft × lights per foot)
strands = ceil(total lights / lights per strand)The defaults describe a 7 ft tree at 100 lights per foot: 7 × 100 = 700 lights, and at 100 bulbs to a set that is 7 strands. Raise the density to 150 and the same tree wants 1,050 lights and 11 strands - the second rounding is why 1,050 / 100 becomes 11 rather than 10.5. Every field must be greater than zero or the tool refuses to calculate.
Choosing the density
For a tree the density is per foot of height, not per foot of wire wrapped round it; the rule of thumb already allows for the spiral. Common settings:
| Look | Lights per foot | On a 7 ft tree |
|---|---|---|
| Sparse | 50 | 350 |
| Standard | 100 | 700 |
| Dense, mantel-magazine | 150-200 | 1,050-1,400 |
Garland and roof lines are entered as their own run length, and they want a much lower density: 100 per foot over a 30 ft porch is 3,000 bulbs. Something near 10-35 per foot is closer to what a lit garland actually carries.
Frequently asked questions
How many lights do I need for a 7 foot Christmas tree?
About 700 at the standard 100 lights per foot. 350 reads as sparse and 1,050 as heavily lit, so the honest answer is a range: seven to eleven 100-bulb strands.
How many lights per foot of garland?
Far fewer than a tree. Leave the density at 100 and a 30 ft porch run asks for 3,000 bulbs; 10 to 35 per foot gives a garland that reads as lit without burying the greenery.
Why does the strand count round up?
You cannot buy two thirds of a light set. The tool rounds the total lights up to a whole bulb and then the strand count up to a whole box, so 640 lights at 100 per strand is 7 boxes with 60 spare.