How Many Christmas Lights Can I String Together?

So, you want to be the next Clark Griswold and light up the neighborhood (and the International Space Station) with your Christmas lights this holiday season. For starters, we applaud you. Second, if that’s the case, then you need to know a few things about how to do it safely. As much as you might want to connect 25,000 lights — the number Clark and Rusty used back in 1989 — there are, in fact, some clear ways to know exactly how many strings of lights are safe for you and your family (and your neighborhood) for Christmas. So, without further ado, let’s dive into the question itself: “How many Christmas lights can I string together at once?”

The Basics of Home Decoration Christmas Lights

There are some very simple ways to determine the number of lights that you can string together for your home. When you get right down to it, only two main things will affect this number: 1) The kind of lights you decided to use, and 2) How many other devices will be running off of the same circuit in your home.

For the kind of lights you use, homeowners basically have two primary options: LED lights or incandescent lights. Incandescent Christmas lights are cheaper at the store, but they cost a lot more to run at home because they use far more electricity.

On the flip side, LED lights require much less power than incandescent light bulbs do. Because of this, you can usually connect more strings of LED Christmas lights together than you would with incandescent Christmas lights.

As for the second point, we highly recommend that you use a dedicated circuit for your holiday lights. It will make doing any math a little easier and save you some potential headaches along the way. (AKA: Get the Griswold look without the Griswold method.)

To do this, just make sure that the outlets you use are only for Christmas lights. You can easily check this by taking a look at your breaker box. Breaker boxes are usually well labeled, so you should be able to determine a dedicated circuit pretty quickly and easily.

If you do happen to overload your outlets, thankfully not much will happen. In modern homes, when a circuit is overloaded with Christmas lights (or anything else, like a hairdryer), then the circuit breaker trips, causing the power to go out from anything on that circuit. All you need to do is move a few lights to a different breaker, then locate the breaker that tripped and reset it.

How to Calculate the Number of Lights for Your House

Once you’ve decided on LED or incandescent lights and picked out a circuit to use for your Christmas lights, you can calculate the number of lights you can string together for your house.

Thankfully, most of the big Christmas lights manufacturers — like Philips, for example — will tell you right on the box how many sets of their lights you can safely string together without any issues.

In other words, if you’re only using one type of light, then all the math is already done for you. Just look on the packaging!

Here’s one example: On a set of Philips 400ct heavy-duty, incandescent, mini-string Christmas lights (clear color) from Target, you can read right on the packaging how many sets you can string together. In this case, the answer is 9 sets of this particular type of light.

There’s literally no math or homework required. Just read the box, and you’re all set. The answer should be right on the front. They want you to be using their products safely as much as you do.

The Rytec Electric Christmas Lights Calculator

Now, if you’re really channeling your inner Christmas Vacation and not just using a single type (or even brand) of Christmas light set, then you may need to do a little more work.

So, once you have each of the necessary pieces of information, you can plug all your numbers into this Christmas Lights calculator and get the answer. No pencil and paper required!

Disclaimer: This calculator is intended for educational purposes only. Rytec is not responsible for any damage to property or persons that may result in the use of electrical equipment such as holiday lights. Please take extreme caution whenever using electricity.

Here’s the Formula for How Many Christmas Lights You Can String Together at Once

All of that being said, if you do want to know the steps and the formula, you can read it in depth below. Please keep in mind that this is not super easy math for most people, which is why we have the calculator above.

First, we will give you the steps by themselves, then a more detailed explanation below of how and why the steps work.

  1. Find out whether you have 15-amp or 20-amp circuits in your house.
  2. For safety, make sure you stay under 80% of any one circuit’s capacity.
  3. Multiply the wattage per strand by the number of strands you want to use to get the total amount of power/wattage required.
  4. Divide 210 by the wattage used per strand to figure out the total number of strands of Christmas lights that you can string together at once.
  5. Use the answers to #3 and #4 to determine how many lights you can use on your house in total and on any one outlet in particular.


  • A house with 15-amp circuits. Each one can take 1800 watts.
    80% of 1800 watts is 1440 watts (the safe limit).
  • The homeowners want to use LED lights requiring 10 watts per strand.
    1440 watts divided by 10 watts is 144 strands (the total that could be plugged into one outlet safely).
  • But, the connected strands should never exceed 210 watts when combined.
    210 watts divided by 10 watts per strand is 21 strands (the total number of strings of these Christmas lights that could be plugged together safely).
  • So, while these homeowners could safely plug 144 strands into one 15-amp outlet in terms of total wattage, the connected lights should never go higher than 210 watts, meaning that only 21 total strands can actually be plugged into each other. Every set of 21 strands would need its own outlet, but not its own circuit.

The Detailed Steps for the Christmas Lights Formula

Here are the detailed explanations for each one of the above steps.

You should never exceed 80% of a particular circuit’s capacity. So, you need to know whether your breakers are 15-amp or 20-amp circuits. This is an important part of figuring out the safe number of Christmas lights you can string together on your home.

An important note: Power strips will not let you plug more strings of Christmas lights together if the power strip itself is connected to a single outlet, because the circuit will be receiving the same number of watts either way.

Now, your home’s 15-amp circuits will be able to safely withstand 1800 watts in total (15 amps x 120 volts). 80% capacity of this is 1440 watts maximum. Your 20-amp circuits can safely take up to 2400 watts in total (20 amps x 120 volts). 80% capacity of this is 1920 watts maximum.

(The type of circuits you have should be indicated on your breaker box, so you shouldn’t have to do too much searching. In turn, this tells you how many Christmas lights per outlet is safe for your home.)

Summary: Never use more than 1440 watts on a single 15-amp home circuit or 1920 watts on a 20-amp home circuit. To find your total Christmas lights wattage, simply multiply the total wattage per strand by the total number of strands. This is the total number of Christmas lights that you can use for any one circuit in your home.


Example: 10 watts per strand x 5 strands = 50 watts.

Next, you should never exceed 210 watts with any set of connected strands of Christmas lights. This is a result of the UL Standards that electrical products follow, whether indoor or outdoor.

You might wonder, “Is there a difference between indoor vs. outdoor lights?” The answer is yes. While some lights can be used in both indoor and outdoor settings, you will want to make sure the tag indicates the right environment for your use.

  • Indoor Christmas lights should have a green UL tag or a silver tag with UL written in green.
  • Outdoor Christmas lights, by contrast, should have a red UL tag or a silver tag with UL written in red.

Another, related question is whether indoor or outdoor lights use more power. As a rule, outdoor lights aren’t any more powerful or brighter necessarily. They just have extra protection on them to keep them safe from the elements and inclement weather like rain or snow.

Naturally, the best bet for homeowners looking to play it safe is to just look for Christmas lights that are tagged for both indoor/outdoor use and get those instead. That way, you don’t have to worry about where you use them.

So, you divide 210 by the total number of watts that each string of Christmas lights uses to get your answer. The answer is the number of strings that you can safely daisy-chain together per home outlet.

Example: 210 (watts) ÷ 10 (watts per strand) = 21 strands of Christmas lights safety strung together.

NOTE: If you’re using different types and brands of lights, then you’ll need to figure out the full combination of wattages used to find the number of strands you can safely string together. The same goes for using an outlet with other home appliances on it, which is why we always recommend using a dedicated “Christmas Lights Only” outlet.


Well, Mr. and Mrs. Griswold, you are now prepared to take on the challenge of lighting up your home with the most beautiful and epic Christmas display the world has ever seen — or at least your neighborhood’s holiday competition.

When you get ready to start connecting all your decorations and plugging them in, just remember that there is a specific answer to the question, “How many Christmas lights can I string together?” And now, you know exactly how to find it and keep you and your family safe from harm (although you still might blind those annoying neighbors).

To quote Aunt Bethany, “Is your house on fire?” We certainly hope not! But for any help you may need with your home electrical work, give the folks at Rytec Electric a call today, where professional quality meets Southern hospitality every time.

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