Grow Tent Power Usage: Grow Light Electricity Cost Calculator
What your grow really costs in electricity — split into vegetative stage and flowering, including exhaust fans and other gear.
Calculated with PlantClue
Why it pays to calculate veg and flower separately
Why?
In most indoor grows, lighting is the biggest power draw, but not the only one: exhaust fans, circulation fans, carbon filter fans, dehumidifiers and heaters often run around the clock and add up to noticeable amounts over the weeks.
Why does it matter?
The vegetative stage (usually 18 hours of light) and flowering (usually 12 hours of light) use very different light cycles. If you calculate the whole grow with a single hours value, your estimate can easily be off by 20–30% from the actual cost.
What to do if costs are high?
The biggest levers: a more efficient LED instead of HPS, a correctly set timer, running the exhaust only as hard as needed, and comparing electricity rates — if you run several grows a year, even switching your electricity plan can save you a noticeable amount.
Example calculations: light wattage & monthly electricity cost
This table shows lighting costs only, per month (30 days, 18 h/day in veg or 12 h/day in flower, $0.17/kWh) — without exhaust, circulation fans or heating. Use it as a quick guide, and the calculator above for your exact setup.
| Light wattage | kWh/day (veg, 18 h) | Cost/month (veg) | kWh/day (flower, 12 h) | Cost/month (flower) |
|---|---|---|---|---|
| 150 W | 2.70 | $13.77 | 1.80 | $9.18 |
| 200 W | 3.60 | $18.36 | 2.40 | $12.24 |
| 300 W | 5.40 | $27.54 | 3.60 | $18.36 |
| 450 W | 8.10 | $41.31 | 5.40 | $27.54 |
| 600 W | 10.80 | $55.08 | 7.20 | $36.72 |
Formula: watts × hours of operation ÷ 1000 = kWh/day; kWh/day × 30 days × electricity price = cost/month. If your electricity price is different or you run extra devices (exhaust, dehumidifier, heater), use the calculator above.
What often gets overlooked when calculating electricity costs
- Only counting the light — exhaust fans, circulation fans, carbon filter fans and dehumidifiers often run 24 hours a day and quickly add up to 50–150 extra watts of constant load
- Assuming the same hours for veg and flower — 18 hours in veg vs. 12 hours in flower makes a clear difference over several weeks
- Not checking your current electricity price — rates can vary a lot by region and over time, and an outdated price skews every estimate
- Only counting the lit stages and ignoring germination (usually a few watts for a short time) — for a very precise calculation, this stage counts too
Cannabis grow electricity costs — FAQ
How do you calculate the electricity cost of a grow?
The light’s wattage times its hours of operation per day gives you watt-hours per day; divided by 1000, that’s kWh per day. Multiply by the number of days and your electricity price per kWh to get the total. Because the vegetative stage and flowering usually have different light cycles, it pays to calculate each stage separately — which is exactly what the calculator above does automatically.
How much does a 300-watt LED cost to run per month?
At 18 hours a day and $0.17/kWh, a 300-watt light uses about 5.4 kWh per day — that’s roughly $0.92 a day, or about $28 a month — for lighting only, without exhaust, circulation fans or heating.
Which devices besides the light drive up electricity costs?
Exhaust fans, circulation fans, carbon filter fans, dehumidifiers and, if used, a heat mat often run around the clock and quickly add up to 50–150 extra watts of constant load. The calculator above counts them as a separate item, “Other devices”.
Is switching from HPS to LED worth it for the electricity savings?
LED lights usually produce more usable light per watt than HPS lamps and give off less waste heat, which also lowers cooling and exhaust costs. Over several grow cycles, the higher purchase price often pays for itself through lower running costs.
Why does the calculator separate the vegetative stage and flowering?
In the vegetative stage, the lights usually run 18–24 hours a day, while in flowering they run only 12 hours (the short-day trigger). If you calculate both stages with the same hours value, you can significantly overestimate or underestimate the actual cost.
