Grow room electricity cost calculator
Estimate the electricity for a full growing cycle. Set your lighting schedule, add equipment and use the price from your electricity bill.
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How we calculate
kWh = W × h × days / 1000. Electricity cost = kWh × price per kWh.
We calculate lamp energy separately for each phase. Device energy uses watts multiplied by quantity, daily running hours and the total days in both phases. Totals exclude equipment purchases, standing charges and other growing costs.
For equal-light comparisons we divide the current lamp’s watts multiplied by its efficacy by the alternative lamp’s efficacy. These are typical photon efficacy assumptions:
- LED: 2.7 µmol/J
- HPS: 1.7 µmol/J
- CMH: 1.9 µmol/J
- CFL: 0.9 µmol/J
Default electricity price source: Eurostat (nrg_pc_204) and U.S. EIA (Electric Power Monthly 5.6.A). Period: Europe 2026 first half, United States August 2026.
Frequently asked questions
Should I enter the advertised lamp watts?
Use the actual power drawn at the wall, not an equivalent or replacement wattage. A plug-in energy meter or the fixture specification can help. If you dim the lamp, use its power at that setting.
Which electricity price should I use?
Use the per-kWh rate on your bill, including taxes and usage-based charges. The regional default is only a starting point. If your tariff changes by time of day, enter an average weighted by when your equipment runs. Fixed daily charges are excluded.
How do I include fans and equipment that switches on and off?
Add each device type with its watts, quantity and average running hours per day. A device running half the day uses 12 hours. All listed devices use that schedule during both growing phases. A passive carbon filter draws no power; add only its fan.
Does switching lamp type guarantee these savings?
No. The comparison estimates equivalent light using typical photon efficacy for each lamp type. Real fixtures, dimming, light distribution and changes in heating or cooling can alter the result. Equipment purchase costs are not included.
What does the cost per gram include?
It divides the estimated electricity cost for the full cycle by your expected dry yield. It does not predict yield or include equipment, water, nutrients or other costs. Leave yield empty if you only want energy and cycle costs.
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