Grow Light Cost Calculator
Grow lights run for 12 to 18 hours a day, so a fixture that looks cheap to buy can quietly become one of the biggest lines on your electric bill. Enter the actual wattage of each light, how many you run, your daily hours and your electricity rate, and this calculator breaks the running cost into per-hour, per-day, per-month and per-year figures, plus the energy used each day in kilowatt-hours.
Use the actual wattage from the label or driver, not the model name. A “600W” LED often draws far less.
Cost per month
$0.00
Estimate only. Real draw varies with dimmer settings, and your rate may include time-of-use pricing or taxes.
Quick Answer
One 600W grow light running 12 hours a day for 30 days at $0.15/kWh uses 7.20 kWh per day and costs $0.09 per hour, $1.08 per day, $32.40 per month and $388.80 per year. The calculator above is pre-filled with this exact setup, so the figures you see on Calculate match this box line for line.
Key takeaways
- The bill follows the actual draw at the wall, not the wattage in the model name. A “600W” LED that really draws 250W costs less than half the estimate its name suggests.
- Hours matter as much as watts. Cutting the photoperiod from 18 to 12 hours cuts the lighting bill by a third, with no new equipment.
- The yearly figure is the month you entered, twelve times over. Enter a typical 30-day month for a realistic year.
- Lights are usually the largest single load in a grow, but fans, pumps and cooling sit on top of the lighting figure.
- Quick Answer
- How to use the grow light cost calculator
- The grow light cost formula
- Worked example: one 600W light on a 12-hour day
- What common wattages cost per month
- Why your real bill runs higher than the estimate
- Three honest ways to cut the lighting bill
- What competing calculators miss
- Frequently asked questions
- Add This Calculator to Your Website
How to use the grow light cost calculator
Enter the draw of one light, how many you run, the daily hours, your rate and the days in the month. Results stay hidden until you click Calculate.
- Wattage per light: read it off the fixture label or the driver, not the box headline. If the label gives amps and volts instead, multiply them for watts, or run the numbers through the amp to watt calculator first.
- Number of lights: count every fixture on the same timer. Leave it blank and the tool assumes one light.
- Hours per day: the photoperiod your timer is set to. Vegetative rooms often run 16 to 18 hours, flowering rooms 12.
- Electricity rate: the $/kWh figure from your bill. If the bill only shows a total charge and total usage, the cost per kWh calculator splits it into the per-kWh rate this tool needs.
- Days per month: 30 for a typical month. The tool accepts up to 31 and refuses more, because no month has 32 days.
Cost is only one half of setting up a light. Once you know what a fixture costs to run, the grow light distance calculator works out how high above the canopy it should hang at each growth stage, which is a separate question with its own math.
The grow light cost formula
The whole calculation is one line: convert watts to kilowatts, multiply by hours and days to get kilowatt-hours, then multiply by your rate.
Cost per day = Energy per day × Rate per kWh
Cost per month = Energy per day × Days per month × Rate per kWh
Cost per year = Cost per month × 12
This is the standard appliance method: the U.S. Energy Information Administration’s data on energy use in homes prices any device the same way, from its wattage and hours of use. Two honest details about how this tool applies it. First, the year is the month you described multiplied by 12, not a 365-day rebuild, so a 31-day month produces a slightly generous year. Second, the rate is treated as flat: if your plan charges more at peak times, the true figure sits between the off-peak and peak runs, and running the tool twice, once per rate, brackets it.
Worked example: one 600W light on a 12-hour day
The pre-filled run is a single 600W light, 12 hours a day, 30 days a month, at $0.15/kWh. These are the exact lines the calculator returns.
| Result line | 600W × 1 light, 12h, $0.15 | 250W × 4 lights, 18h, $0.17 |
|---|---|---|
| Total wattage | 600 W | 1,000 W |
| Energy per day | 7.20 kWh | 18.00 kWh |
| Cost per hour | $0.09 | $0.17 |
| Cost per day | $1.08 | $3.06 |
| Cost per month | $32.40 | $91.80 |
| Cost per year | $388.80 | $1,101.60 |
The second column is the useful comparison: four smaller lights on an 18-hour vegetative schedule draw more total power and run longer, so they cost nearly three times as much as the single bigger light on a 12-hour flowering schedule. Fixture count and hours usually move the bill more than the headline wattage does.
What common wattages cost per month
At the same 12 hours a day, 30 days and $0.15/kWh, monthly cost scales in a straight line with wattage. Every figure below is a run of the tool above with one light.
| Light wattage (actual draw) | Cost per month | Cost per year |
|---|---|---|
| 100 W | $5.40 | $64.80 |
| 200 W | $10.80 | $129.60 |
| 400 W | $21.60 | $259.20 |
| 600 W | $32.40 | $388.80 |
| 1,000 W | $54.00 | $648.00 |
Rates change the picture as much as wattage does. The U.S. Energy Information Administration’s Electric Power Monthly, Table 5.6.A publishes average residential prices by state, and the spread is wide: the same 600W setup that costs $32.40 a month at $0.15/kWh costs about $69 in a $0.32/kWh state. Run the tool with your own rate before trusting any table, including this one.
Why your real bill runs higher than the estimate
The calculator prices the lights exactly as entered. Bills come in higher when the inputs understate the room, and four causes account for nearly every gap.
- Advertised wattage instead of actual draw cuts both ways. Costing a “600W” LED at 600 when it draws 250 overstates the bill; costing an HID bulb at its lamp wattage understates it, because the ballast adds roughly 10 to 15 percent on top.
- A rate that leaves out delivery and taxes. The generation price on a bill is often only half the all-in per-kWh cost. Use the all-in figure.
- Everything else in the room. Fans, pumps, dehumidifiers and cooling all draw power on the same meter. The grow room cost calculator takes the next step out and adds setup and maintenance to the electricity for a whole-cycle room budget, while this page stays on the lights alone.
- The grow inside the household bill. To judge what the grow does to the total at the meter, the cost of energy calculator prices your other appliances on the same rate so the lighting figure has something to be compared against.
Three honest ways to cut the lighting bill
Only three levers exist: fewer watts, fewer hours, or a cheaper rate. Anything else is packaging.
- Right-size the wattage. An efficient modern LED delivers the same plant-usable light as an older fixture at a lower draw. The saving shows up in the wattage input, and the tool prices it exactly.
- Trim the photoperiod to what the stage needs. Seedlings do not need 18 hours at full power, and every hour removed is an hour you stop paying for across every light in the room.
- Use off-peak hours if your plan offers them. On a time-of-use plan, shifting the light cycle so the dark period covers the expensive afternoon window can cut the effective rate without changing the plants’ schedule length at all.
What competing calculators miss
Most tools ranking for this keyword answer a narrower question than growers actually ask:
- Home Kitchen Magazine’s grow light electricity calculator: the closest rival, with the same five inputs and a currency selector. It reports daily and monthly energy and an annualized cost, but never the per-hour figure that makes timer decisions easy.
- Hydrobuilder’s grow room electricity calculator: thorough, and it will happily cost your fans, AC and pumps too. For the narrower question “what do the lights cost” it is more machine than most readers need, and it still assumes you know your true draw.
- Royal Queen Seeds and the guide sites: the formula is right and the true-watts warning is well explained, but the math is left as worked examples in prose. There is no tool to run with your own rate.
- Generic electricity cost calculators: correct appliance math with no grow context at all: no multi-light input, no photoperiod framing, no actual-draw warning where it matters.
- The gap this page fills: per-hour, per-day, per-month and per-year figures in one run, any number of lights, the actual-wattage check printed at the inputs, a published cost table you can verify against the tool, and an open note that the year is the entered month times twelve.
Frequently asked questions
Multiply watts divided by 1,000 by hours per day, days per month and your rate per kWh. One 600W light at 12 hours a day, 30 days a month and $0.15/kWh costs $0.09 per hour, $1.08 per day, $32.40 per month and $388.80 per year.
Less than HID lights for the same plant-usable output, but the long daily hours still add up. Always cost the actual draw from the label: a light sold as 600W may draw only 250W, which cuts the monthly estimate by more than half.
Look for the per-kWh price on your electric bill. Use the all-in rate including delivery charges and taxes if you want the figure your bill actually follows, and check whether your plan charges different prices at different times of day.
Seedlings and vegetative plants commonly get 16 to 18 hours, and flowering plants usually get 12. The hours input moves the bill in direct proportion, so dropping from 18 to 16 hours cuts the lighting cost by about 11 percent.
At 12 hours a day, 30 days a month and $0.15/kWh, a true 1000W draw costs $54.00 per month and $648.00 per year. Run it 18 hours a day instead and the same math gives $81.00 per month.
Because the tool costs the month you describe and repeats it twelve times. If your days per month is 31, the year figure assumes twelve 31-day months, so for a budget year enter a typical month, usually 30 days.
An HID ballast typically adds about 10 to 15 percent on top of the bulb wattage, so raise the wattage input by that amount for an HID rig. Fans and pumps draw far less than the lights, but on a large setup they are worth adding into the wattage or costing separately.
Only if your plan has time-of-use pricing with cheaper off-peak hours. On a flat rate the clock changes nothing, because the tool and your meter both charge the same per kWh whenever the lights are on.
Yes, and the energy per day figure is the number you size the system with. The worked example uses 7.20 kWh per day, which needs a substantial panel array and battery bank, so most growers stay grid-tied or offset only part of the load.
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References
- U.S. Energy Information Administration. Use of Energy in Homes. Accessed October 21, 2026.
- ENERGY STAR. Light Bulbs At A Glance. Accessed October 21, 2026.
- U.S. Energy Information Administration. Electric Power Monthly, Table 5.6.A: Average Price of Electricity to Ultimate Customers by End-Use Sector. Accessed October 21, 2026.
- U.S. Energy Information Administration. Frequently Asked Questions: How Much Electricity Does an American Home Use? Accessed October 21, 2026.
- U.S. Energy Information Administration. Electric Sales, Revenue, and Average Price. Accessed October 21, 2026.
- ENERGY STAR. Light Bulbs At A Glance. Accessed October 21, 2026.