# How much electricity does a home grow use?

> A home grow uses about 300 kWh per photoperiod run in a 2 x 2 ft tent (150 W LED plus fans) and about 850 kWh in a 4 x 4 ft tent (500 W LED plus fans), with 4 weeks of veg at 18/6 and 10 weeks of flower at 12/12. At 0.15 per kWh that is roughly 45 and 130 in local currency. Dehumidifiers and heaters add more.

- Canonical: https://genetixbay.com/knowledge/answers/electricity-cost-of-growing.html
- Topic: Basics · Type: Numbers
- Evidence: Established · Status: Draft: awaiting expert review
- Full article: [Your first grow: a plan from seed to jar](https://genetixbay.com/knowledge/basics/first-grow-guide.md)
- Also asked as: Electric bill for growing weed | Cost to run a grow light | How much does it cost to grow at home? | How many kWh does a grow tent use?
- Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)"

## Short answer

A small [home grow](https://genetixbay.com/knowledge/glossary/home-grow.md) uses about 300 kWh per [photoperiod](https://genetixbay.com/knowledge/glossary/photoperiod.md) run in a 2 x 2 ft tent and about 850 kWh in a 4 x 4 ft tent, with 4 weeks of veg at [18/6](https://genetixbay.com/knowledge/glossary/18-6.md) and 10 weeks of flower at [12/12](https://genetixbay.com/knowledge/glossary/12-12.md). The light is most of it. *Established*: it's arithmetic, kWh = watts × hours ÷ 1,000.

## Why

Indoor growing is energy-hungry at scale. One estimate put indoor cannabis at about 1% of US electricity use [1]. At home the same physics applies, just smaller.

The light dominates, and [efficacy](https://genetixbay.com/knowledge/glossary/photon-efficacy.md) sets its cost. Good [LEDs](https://genetixbay.com/knowledge/glossary/led.md) exceed 2.5–3 µmol/J [3]. In one trial, the best LED fixture gave about 27% more flower per dollar of electricity than a [double-ended HPS](https://genetixbay.com/knowledge/glossary/hps.md), at about 1.1–1.3 cents per mole of light against 1.6 cents at 0.10 per kWh [2].

Hours matter as much as watts. 18/6 veg uses 50% more lighting energy per day than 12/12 flower, and [24/0](https://genetixbay.com/knowledge/glossary/24-0.md) uses double.

Climate gear is the hidden bill: a [dehumidifier](https://genetixbay.com/knowledge/glossary/dehumidifier.md) or heater can rival the light.

## The numbers

| Setup | Daily use | Run total | At 0.15/kWh |
|---|---|---|---|
| 2 x 2 ft: 150 W LED + 40 W [fans](https://genetixbay.com/knowledge/glossary/fan-leaf.md), veg 18/6 | 3.7 kWh | 28 days ≈ 100 kWh | |
| Same, flower 12/12 | 2.8 kWh | 70 days ≈ 195 kWh | |
| **2 x 2 ft photo run** | | **≈ 300 kWh** | **≈ 45** |
| 4 x 4 ft: 500 W LED + 80 W fans, veg 18/6 | 10.9 kWh | 28 days ≈ 305 kWh | |
| Same, flower 12/12 | 7.9 kWh | 70 days ≈ 555 kWh | |
| **4 x 4 ft photo run** | | **≈ 860 kWh** | **≈ 130** |
| 2 x 2 ft [auto](https://genetixbay.com/knowledge/glossary/autoflower.md), 20/4 for 11 weeks | 4.0 kWh | ≈ 305 kWh | ≈ 46 |
| Add: 300 W dehumidifier, half the time | 3.6 kWh | +350 kWh per 14 weeks | +53 |

Use your own tariff.

## What to do

1. Use the light's real wall wattage, ideally read from a plug-in energy meter.
2. Add every device and its daily hours.
3. Buy fixture efficacy (µmol/J); it pays back every day.
4. Keep the tent in a room that is already near target temperature and [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md).
5. Keep continuous load under 80% of the circuit rating [4].

## Common mistakes

- Using a fixture's "equivalent" wattage.
- Forgetting fans run 24 hours.
- Ignoring the dehumidifier or heater.

## Related

- Full article: [Your first grow](https://genetixbay.com/knowledge/basics/first-grow-guide.md)
- Guide: [Electrical and water safety](https://genetixbay.com/knowledge/guides/electrical-and-water-safety.md)
- Answers: [fire risk](https://genetixbay.com/knowledge/answers/grow-room-electrical-safety.md) · [what wattage for my tent](https://genetixbay.com/knowledge/answers/what-wattage-light-for-my-tent.md) · [LED vs HPS](https://genetixbay.com/knowledge/answers/led-vs-hps.md)
- Terms: [photon efficacy](https://genetixbay.com/knowledge/glossary/photon-efficacy.md) · [LED](https://genetixbay.com/knowledge/glossary/led.md)

## Follow-up questions

**How do I calculate my grow's electricity use?** To calculate a grow's electricity use, multiply each device's real wattage by the hours it runs per day and divide by 1,000 to get kWh per day. Add up the light, fans, dehumidifier and heater, multiply by the days in each stage, then by your price per kWh. A plug-in energy meter gives the real numbers instead of label figures.

**Do autoflowers use more electricity?** Autoflowers use more lighting power per day than flowering photoperiods, because they run 18–20 hours of light rather than 12, but they finish in about 9–14 weeks with no separate veg. A 150 W auto run at 20/4 for 11 weeks uses about 300 kWh with fans, close to a photoperiod run with 4 weeks of veg in the same tent.

**Are LEDs cheaper to run than HPS?** Efficient LEDs are cheaper to run than HPS for the same light at the plants. In one trial, the best LED fixture made about 2.5 µmol of light per joule against 1.7 for a double-ended HPS, and produced about 27% more flower per dollar of electricity. Whether LED or HPS grows better buds is a separate, open question GenetixBay is testing in a Bay Trial.

## Sources

1. Mills E, 2012. The carbon footprint of indoor Cannabis production. Energy Policy 46:58-67. https://doi.org/10.1016/j.enpol.2012.03.023
2. Westmoreland FM, Kusuma P, Bugbee B, 2021. Cannabis lighting: Decreasing blue photon fraction increases yield but efficacy is more important for cost effective production of cannabinoids. PLoS ONE 16(3): e0248988. https://doi.org/10.1371/journal.pone.0248988
3. Kusuma P, Pattison PM, Bugbee B, 2020. From physics to fixtures to food: current and potential LED efficacy. Horticulture Research 7:56. https://doi.org/10.1038/s41438-020-0283-7
4. National Fire Protection Association. NFPA 70, National Electrical Code (continuous loads at 80 % of branch-circuit rating; GFCI requirements). https://www.nfpa.org/codes-and-standards/nfpa-70-standard-development/70