Grow light running cost calculator
Enter your wattage, your hours and your state. See what the light actually costs to run per day, per month, per year and per harvest.
Total running cost
$0.00 per month
Show the maths
Default rates: May 2026 average residential prices from the US Energy Information Administration, Electric Power Monthly, Table 5.6.A. They are state averages, so your own bill is always the better number. Estimates exclude fixed monthly service charges, because those do not change when you switch a light on.
Electricity is the one running cost of indoor growing that never stops. The equipment is a one-off, the nutrients are a few dollars a year, but the light draws power every single day you run it. This tool tells you exactly how much, using average residential rates for your state.
What a grow light actually costs to run
Most beginners expect a frightening number and are relieved by the real one. At the US average residential rate of 18.44¢ per kWh, here is what four common setups cost.
| Setup | Actual draw | Hours/day | Per month | Per year |
|---|---|---|---|---|
| One jar of herbs on a windowsill with a desk LED | 30 W | 14 | $2.36 | $28 |
| A shelf of lettuce | 100 W | 14 | $7.86 | $94 |
| A 2×2 ft tent | 150 W | 16 | $13.47 | $162 |
| A 4×4 ft tent | 480 W | 16 | $43.11 | $517 |
Where you live matters more than what you grow
The same 2×2 tent, running 16 hours a day, uses 877 kWh a year wherever it is plugged in. What changes is the price of that electricity, and the spread across the US is enormous.
| State | Rate | Cost per year to run that tent |
|---|---|---|
| Idaho (cheapest) | 12.35¢ | $108 |
| Texas | 16.44¢ | $144 |
| US average | 18.44¢ | $162 |
| California | 33.25¢ | $291 |
| Hawaii (most expensive) | 52.00¢ | $456 |
If you are in a high-rate state, efficiency is worth paying for up front. If you are in a low-rate state, an extra 50 W matters far less than getting the light close enough to the canopy.
How the calculation works
No mystery here. The whole thing is one line of arithmetic:
(watts ÷ 1000) × hours per day × price per kWh = cost per day
- Divide by 1000 because electricity is billed in kilowatt-hours, and a watt is a thousandth of a kilowatt.
- Multiply by hours because a 100 W light on for 14 hours uses the same energy as a 1400 W appliance on for one hour.
- Multiply by your rate to turn energy into money. Our default is your state average, but the number on your own bill is always better.
- Month uses 30.44 days and year uses 365.25, which are the true averages. Multiplying a daily figure by 30 undercounts by about 1.5%.
Use the real wattage, not the number on the box
This is the single biggest source of wrong answers. Grow light listings routinely advertise things like “1000 W equivalent” for a panel that draws 100 W from the wall. The equivalent figure is a marketing comparison against old HPS lamps and has no agreed definition.
What you want is the actual power draw, sometimes listed as “power consumption” or “wall draw”. If a listing will not state one, that is informative in itself.
More on reading a spec sheet honestly in our grow light buying guide
The costs almost every calculator forgets
Most grow light calculators stop at the light. But a hydroponic system usually has other things plugged in, and several of them run around the clock rather than on a timer. Twenty-four-hour operation adds up faster than people expect.
| Equipment | Typical draw | Hours/day | Cost per year at 18.44¢ |
|---|---|---|---|
| Air pump (DWC) | 4 W | 24 | $6 |
| Water pump (NFT or drip) | 5 W | 24 | $8 |
| Seedling heat mat | 20 W | 24 | $32 |
| Small inline fan | 25 W | 24 | $40 |
None of these is alarming on its own, but a tent with a fan, a pump and a heat mat quietly adds around $80 a year on top of the light. The calculator above lets you add each one, which is why it starts with an air pump already in the list.
Nine ways to cut the cost, most of them free
Cut the photoperiod to what the crop needs
Lettuce and herbs do not benefit much beyond 14 hours. If you are running 18 out of habit, you are paying about 30% more than you need to for no extra growth.
Move the light closer instead of turning it up
Light intensity falls off sharply with distance. Lowering a panel from 24 inches to 12 delivers far more usable light to the canopy at exactly the same wattage.
Put reflective material around the grow
White card, a painted wall or cheap mylar bounces light that would otherwise miss the plants entirely. It is the closest thing to free extra wattage.
Fill the footprint
A 150 W panel lighting two plants costs the same as one lighting six. Cost per plant, not cost per system, is the number that matters.
Run lights overnight if you are on a time-of-use plan
Many utilities charge much less off-peak. Plants have no opinion about which hours are dark, so shifting the photoperiod is free money on the right tariff.
Use a timer, always
A $5 mechanical timer prevents the most expensive mistake there is: forgetting to switch the light off for a weekend.
Take the heat mat off once seeds germinate
It has done its job in a week or two, and it is often the second-largest draw in a small setup.
Clean the panel
Dust and hard-water spatter on a diffuser measurably cut output. Thirty seconds with a dry cloth every few weeks costs nothing.
Grow the crops that repay the light
Herbs and salad leaves are expensive to buy and quick to grow. Potatoes are neither. Match what you grow to what you actually pay for at the store.
Is an efficient light worth the extra money?
Usually yes, but the maths depends on your rate. Suppose you are choosing between a $40 panel drawing 200 W and a $75 panel drawing 150 W for the same coverage, running 16 hours a day.
The cheaper panel uses 292 kWh more per year. At the US average that is about $54 a year, so the $35 price difference pays for itself in roughly eight months. In Idaho it takes over a year. In California it takes about four months, and after that the efficient panel is simply cheaper to own.
Frequently asked questions
How much does it cost to run a grow light per month?
At the US average of 18.44 cents per kWh, a 150 W light running 16 hours a day costs about $13.47 a month. A small 30 W herb light costs about $2.36 a month, and a 480 W tent light about $43. Your own rate matters more than any of these figures, so use the calculator with the number from your bill.
Do grow lights use a lot of electricity?
Less than most people assume. A typical home setup uses somewhere between 10 and 250 kWh a month, which is comparable to a second refrigerator at the top end and a few LED bulbs at the bottom. The cost only becomes significant with multiple large tents.
Should I use the wattage printed on the box?
Only if it is the actual power draw. Many listings advertise an “equivalent” wattage, which compares the panel to an old HPS lamp and is not a measurement of anything. Look for “power consumption” or “wall draw”, or measure it with a plug-in energy meter.
Does the calculator include my fixed monthly charge?
No, deliberately. That charge applies whether or not you grow anything, so including it would overstate what growing actually costs you. The figures here show only the amount your bill goes up.
How many hours a day should I run a grow light?
Ten to fourteen hours for lettuce and leafy greens, twelve to sixteen for herbs, and fourteen to eighteen for tomatoes and peppers. Plants need a dark period, so running a light around the clock wastes money and stresses the plant.
Where do the state electricity rates come from?
They are average residential prices published by the US Energy Information Administration in its Electric Power Monthly report, using May 2026 data. They are state-wide averages, so your utility and tariff may differ noticeably. Enter your own rate for an exact answer.
Is it cheaper to run one big light or several small ones?
What matters is total watts and how well the light lands on your plants, not the number of fixtures. One panel that covers the whole footprint usually beats several small ones that overlap and waste light on the walls.
Now build something to put under it
Every plan on this site is free, and the cheapest one costs about $10 and takes fifteen minutes.