Planning & Calculators
Christmas light wattage and amp calculator
Enter what you are running. The calculator totals the watts, converts to amps and checks it against the 80 percent continuous-load budget for your circuit.
Mike M. — The hands-on owner behind Iron Mako Media.
Published
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Every light set has its wattage printed on the plug tag or the box. This calculator adds them up, converts the total to amps at 120 volts, and compares it with the working budget of a standard household circuit.
Wattage and amp calculator
Enter the wattage printed on each set’s plug tag and how many of them you are running.
| What | Watts each | How many | Subtotal |
|---|---|---|---|
| — | |||
| — | |||
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Budget on a 15 A circuit is 1440 W — that is 80 percent of its 1800 W capacity, the standard allowance for a load running more than three hours.
Enter the wattage from your light sets’ plug tags to see a result.
This totals the load you enter. It does not know what else is already on that circuit, the condition of your wiring, or whether the outlet is correctly GFCI protected. It also does not check the separate end-to-end connection limit printed on each set’s tag. If a breaker trips repeatedly, stop and have it looked at.
What the budget number means
A 15-amp circuit at 120 volts carries 1,800 watts at its absolute limit. The long-standing continuous-load convention in electrical practice is to plan to 80 percent of a breaker's rating for anything running for three hours or more, which a Christmas display obviously is. Eighty percent of 15 amps is 12 amps, or 1,440 watts, and that is the number this tool checks against.
The 20 percent you are leaving unused is not wasted. It is the headroom that absorbs the cold-start surge, the other things already on that circuit, and the fact that breakers age.
Finding the wattage of your sets
- On the tag. Most sets have a small plastic tag near the plug with the wattage and the maximum end-to-end connection count.
- On the box. If you kept it, the specification panel has it.
- On the listing. Search the exact product name; the manufacturer's own listing will state it.
- If you genuinely cannot find it, do not guess wildly. LED C9 sets of 25 bulbs are typically in the low single-digit watts, and mini LED sets of 100 bulbs typically under 10 watts — but use the real figure if you can get it, because incandescent sets are a completely different order of magnitude.
The other limit, which this tool cannot check
Circuit capacity is one constraint. The second is the maximum number of sets you may connect end to end, printed on each set's own tag and usually between three and six for C9. That limit exists because the wire in the first set carries the current for everything downstream of it.
You can be comfortably inside your circuit budget and still be chaining too many sets. The answer to a run that is too long is a second feed from the outlet, not a longer chain. How many lights on one circuit works through both limits together.
What to do if you are over budget
- Switch incandescent runs to LED. This is almost always the whole answer — the saving is an order of magnitude, not a percentage.
- Split across two circuits. A second outdoor outlet on a different breaker, or a run from a garage outlet, doubles your budget.
- Drop the inflatables onto their own feed. Blower motors are a small but real load and they are easy to separate.
- Reduce the display. Fewer, better-placed runs usually look better than more.
Once the numbers work, move on to choosing the lights or straight to best outdoor extension cords for the cord that will carry it.
What to buy
The products that fit the advice above, chosen by the process on our methodology page. We have not hands-on tested them; specifications are the manufacturers’ own.
Quick picks
| # | Product | Best for | Score | Price |
|---|---|---|---|---|
| 1 |  Top pickDEWENWILS Outdoor Digital Timer, 3 outlets, 15A15 A, 3 grounded outlets, 7-day | A whole display on one schedule | 9.1 | Check price on Amazon |
| 2 |  Southwire 14/3 SJTW Outdoor Extension Cord, lighted end14/3 SJTW, 13 A rated | The standard run from house to display | 9.0 | Check price on Amazon |
| 3 |  Kasa Smart Outdoor Plug (KP400)2 independent outlets, sunset offset | Sunrise/sunset scheduling and phone control | 8.8 | Check price on Amazon |
#ad We may earn a commission · Prices are shown by Amazon, not by us
Scores are our own editorial judgment from published specifications and buyer feedback — not aggregated user ratings, and not from hands-on testing. See how we pick.
Jump to a full review below: planning
Common questions
How do I calculate the amps of my Christmas lights?
Add the wattage of every set, then divide the total by 120. A display totaling 600 watts draws 5 amps. Compare that against 12 amps, which is the 80 percent continuous-load budget for a 15-amp circuit.
Why use 80 percent of the circuit rating instead of 100?
It is the standard continuous-load convention for anything running three hours or more. The remaining headroom absorbs startup surge, whatever else is on that circuit, and normal breaker aging. Planning to the full rating is how a display trips on a cold evening.
How many watts does a string of LED Christmas lights use?
Far less than incandescent, but check your own tag rather than using a rule of thumb — draw varies with bulb type, bulb count and whether the set has a controller. The figure is printed on the plug tag or the box.
Sources
Every specification quoted on this page comes from the manufacturer’s own published information or a current retail listing, linked below. Where a figure is not published, we say so rather than estimating it.