How many Christmas lights does a tree need?

Every guide answers this in bulbs — 400 for a six-foot tree, 100 per foot, pick a number. It is the wrong unit. Two strings with the same bulb count can differ in length by three times over, and length is what has to reach round the tree.

Written by the people who manufacture festive light strings and the controllers inside them. Last reviewed July 2026.

Why bulb counts mislead

A light string has two numbers that matter: how many bulbs, and how far apart they sit. Multiply them and you get the only figure that helps you, which is the lit length of the string.

Across the strings we build, bulb spacing runs from roughly 5 cm on dense decorative strings up to 15 cm or more on long garden strings. So a 200-bulb string is anywhere from 10 m to 30 m long. If you buy on bulb count alone, you are buying blind — and it is why so many people end up either short by a third or with 8 m of string left in the box.

The arithmetic that actually works

How much string a tree takes depends far more on how you wrap it than on how tall it is. There are two methods, and they differ by roughly three times. Almost all the confusion about tree light quantities comes from guides quoting one number without saying which method it assumes.

Method A — spiral wrap around the outside

You spiral the string around the outside of the tree, following its silhouette. Fast, and the effect is a lit outline.

Measure the tree height h and its widest diameter d, both in metres. A tree is roughly a cone, so its average diameter is about half its widest, and one turn around it is about π × d ÷ 2. Pick a vertical gap between turns — 20 cm gives a full look, 30 cm is sparser:

A 1.8 m tree, 1.1 m across, wrapped at a 20 cm gap: 9 turns × 1.73 m ≈ 16 m of string.

Method B — branch by branch

You run the string out along each branch and back toward the trunk, so the light sits inside the foliage as well as on the surface. This is what makes a tree look lit from within rather than wrapped in a band, and it is what most people actually want when they say a tree looks "professionally done".

It also consumes far more string. Take your Method A figure and multiply by 2.5 to 3. The same 1.8 m tree needs 40 to 48 m.

These assume a normally proportioned tree at a 20 cm wrap gap. A slim or pencil tree needs less; a wide farm-grown tree needs more. Measure your own diameter rather than trusting the row.

The part nobody tells you: how many strings, not how much string

Length gets you to the shop. What decides whether the install works is how you split that length across separate strings — and this is where our own returns and support questions concentrate.

Take the 1.8 m tree needing 45 m branch-wrapped. You could buy one 45 m string or three 15 m strings. The three shorter strings are almost always the better buy:

• One dead string is not one dead tree. On a single long run, any fault takes the whole tree out. Split across three, you lose a third and the tree is still usable while you sort it out.
• You can wrap in sections. Bottom third, middle, top. Far easier alone, and much easier to fix a patch that looks thin without unwinding everything.
• Packing away is survivable. A 45 m string tangles into a single knot that takes an evening. Three 15 m strings do not.
• Long runs dim toward the far end. The further from the supply, the more voltage the conductors have already dropped. On a short string it is invisible; near the maximum length for that design, the tail is measurably duller than the head.

Warm white, cool white, or colour?

A practical note rather than a taste one. Warm white sits around 2700K and reads as candlelight against green foliage. Cool white above 5000K reads blue-ish and, on an artificial tree, tends to reveal the plastic. If you are mixing colour and white on the same tree, put the white string on first and the colour over it — reverse it and the colour disappears into the interior.

If your string is a colour-changing type, check which app runs it before you start wrapping, because on some models pairing is easier with the string still in the box: see which app controls your light.

Half the string went dark — what that tells you

This is the single most common festive-season question we get, and the answer depends on how the string is built. The pattern of the failure identifies the type.

Everything after one point is dark, everything before it is fine

A clean split like this means the string is a chain and the chain is broken at that point. On an addressable string, each bulb passes the data signal to the next; if one stops passing it, every bulb downstream has power but no instruction, so it stays off. The last lit bulb is your marker — the fault is at it or in the joint immediately after.

Scattered bulbs out, no pattern

Individual bulbs failing independently means they are wired in parallel, which is what we use on most modern LED strings precisely so that one failure does not cascade. Annoying to look at, harmless electrically, and it does not spread.

A whole section flickers together

Sections flickering as a group point at the connection feeding that section rather than at any bulb. Most often it is a plug that is seated but not fully home, or a joint that has taken water in an outdoor install.

The string works until you move it

Intermittent-when-flexed is a conductor problem inside the sleeve, usually within 30 cm of a plug where the wire has been bent repeatedly across seasons. It will get worse. Note where it is when you pack up, so you are not diagnosing it again next December.

Packing them away so they work next year

Most strings that fail in December failed in January. Three things account for nearly all of it:

1. Wind onto something, never into a ball. A length of stiff card or a reel. Balled string gets untangled by pulling, and pulling is what breaks conductors at the plugs.
2. Store the controller box padded and dry. The controller and battery box are the parts that do not tolerate a damp loft or a cold garage across a whole year. Inside the house is better, even if the tree lives in the garage.
3. Take the batteries out. On battery-powered strings this is the one that ruins hardware outright. A cell left in for eleven months can leak and corrode the contacts beyond recovery.

The other option: a light shaped like a tree

Everything above assumes you are wrapping a tree you already own. The alternative is a light that is the tree: strands drop from a single point at the top to a hoop at the base and hold the cone by themselves, so the spacing is set by the frame rather than by how evenly you wrapped.

The trade is straightforward. The arithmetic above disappears: there is nothing to measure and no way to under-buy. In exchange you need somewhere to hang it from, floor space for the hoop, and an acceptance that it reads as a tree across a room and as a cone of strands from a metre away. Where the tree is looked at rather than decorated — a shop window, a stairwell, an entrance — it is usually the easier answer.

Still deciding what to buy?

Work out your length with Method A or B, divide it into runs of 10–20 m, check the per-chain limit on the packaging, and confirm the spacing is stated at all. That is the whole job. If you want the tree to also run effects rather than sit on one colour, check the control app first — the app has to match the controller, and a festive string is the product line where people most often download the wrong one.

Questions about a specific string of ours? Contact us.