Ideas & guides · Lighting

How Many Christmas Lights Do I Actually Need?

You have a roofline and a shelf of boxes all shouting different numbers of feet. How many sets is that, actually?

6 minute read. Checked 29 September 2026.

The box is measured end to end, including the bit that does nothing

A string light set has lead wire at one or both ends: the cable that gets from the outlet to the first bulb. It is part of the length printed on the front of the box and it is not part of the length that lights up. The difference has a name — lit length — and it is the only figure worth dividing by.

On some sets the lead is a few inches and nobody cares. On others it is a 16 ft lead on each end of two 33 ft lit runs, sold as "98 ft", where a third of what you carried to the car decorates nothing at all.

Every light set on this site records the lit figure rather than the headline, which is why the numbers below are smaller than the ones on the packaging. They come straight out of the catalogue, along with everything else the listings bury — you can download the lot if you would rather check than take our word for it.

What a set actually covers

Every figure here is read from the product record when this page loads, so it cannot drift away from what the plans are buying.

Three of these cost within a few dollars of each other and cover between 16 and 70 feet. Per foot is the only comparison that means anything, and it is never the comparison the shelf invites you to make.

Big bulbs are for outlines, small bulbs are for filling

The price gap above is not a trap, it is a job difference. C9 bulbs are large, individually visible points of light, and they read cleanly along a roofline from the street. Mini lights disappear into a shape and light it as a mass, which is what you want in a shrub, a railing or a wrapped trunk.

So the sum is usually two sums. The roofline in C9 at $1.69 a foot, because that is the line people actually see, and everything else in mini lights at $0.37 a foot, because in a bush nobody can tell. Doing the whole house in C9 is how a lighting budget disappears before the lawn has anything on it at all.

One decision comes before either sum, and it is not a matter of taste so much as a matter of not mixing: pick warm or cool and buy the whole run in it. Which one suits your house depends mostly on what the walls are made of.

Measuring the roofline

Stand at the sidewalk and count the horizontal edges you want lit. The main front gutter is one. A porch roof is a second, and it is the one people forget, because from the front door it does not look like a separate run.

Add them, divide by the lit length, round up. Never round down and never buy exactly enough: the run has to get around a corner, past a downpipe and back to a socket, and the last set is always the one that turns out to be short.

On a 54 ft front with an 11 ft porch edge, that is 65 ft, which is five 16 ft C9 sets and not four. If you have not measured the front of the house yet, that is two numbers and ten minutes and it settles this question and several others.

A corner lot is the case that catches people out, because it has two street-facing rooflines rather than one and the second is not optional — an unlit side elevation reads as the half you did not finish. Budget for close to double.

Three sets, three jobs

Lit lengths, not box lengths. Divide your roofline by these.

Prices are what the retailer listed when it was last checked. They move, especially in the last three weeks before a holiday.

Two limits that decide how many you can actually run

Counting sets tells you what to buy. Two separate numbers decide whether you can plug them all in, and both are easier to check now than in the dark in December.

The first is how many sets the manufacturer allows end to end. It is printed on the tag near the plug and it is usually three to five for LED and as few as two or three for incandescent. Past that you are not running a longer string, you are running an overloaded one, and the failure is at the plug rather than at the bulb.

The second is the circuit. Lights are a rounding error next to anything with a motor — a C9 set draws about 0.2 A and an inflatable blower runs all night — so the lights rarely fill a circuit on their own, but they are what tips one over once the inflatables are on it. The arithmetic is worth doing once.

And the cable that gets power out to the run matters more than people expect over distance: too thin and the far end of the roofline is visibly dimmer than the near end. Size the cord by the length of the run, not by what is cheapest on the shelf.

Where this usually goes wrong

Dividing by the number on the front of the box

It includes lead wire. Find the lit length in the specification block, sometimes called illuminated or lighted length, and divide by that. This is the single most common reason a run finishes short.

Forgetting the porch edge

The porch roof is a second horizontal run and it is the one nobody counts, because from inside the house it reads as part of the same roof. From the street it is a separate line and an unlit one is very obvious.

Lighting the whole house in C9

At $1.69 a lit foot it is more than four times the price of mini lights at $0.37. C9 earns that on the roofline, where the individual bulbs are the point. In a hedge it is money spent on bulbs nobody can resolve.

Buying exactly enough

The measured length is never the installed length. Corners, downpipes and the run back to the socket all eat cable, and the shortfall always appears at the last set, in the cold, with the ladder already up.