Grow Room Electricity Calculator
Estimate daily and monthly electricity costs for your indoor grow room lights, fans, and pumps.
About this calculator
Daily Usage sums three separate power draws, each converted from watts to kilowatt- hours by multiplying by the hours it actually runs and dividing by 1,000. Lights only draw power for Light Hours per Day (so a plant on an 18-hour vegetative schedule burns far more light-hours than one on a 12-hour flowering schedule at the same wattage), while fans and pumps are both modeled as running continuously, 24 hours a day, since ventilation and hydroponic circulation typically don't stop just because the lights are off. Because Light Wattage is both the largest single number among the three power draws in a typical setup AND the only one whose runtime is itself adjustable (Light Hours per Day), it is normally the single biggest driver of Daily Usage — a big fan or pump adds a smaller, flatter 24-hour load on top.
Monthly Usage is simply Daily Usage x 30 (a flat 30-day approximation, not the exact days in your specific month), Monthly Cost multiplies Monthly Usage by your entered Electricity Rate, and Annual Cost is Monthly Cost x 12. This is a straightforward wattage-and- runtime model with no allowance for equipment efficiency losses, seasonal rate changes, or tiered utility pricing — treat the outputs as a reasonable planning estimate for comparing setups, not a guaranteed utility bill.
Inputs
Results
Monthly Cost
$34.16
Annual Cost
$409.92
How to Use This Calculator
- Enter the total wattage of all your grow lights (e.g., 400W HPS or 240W LED) and the hours they run per day.
- Enter fan wattage (total of all inline and oscillating fans, typically run 24/7) and pump wattage for hydro systems.
- Enter your electricity rate in $/kWh — find this on your utility bill.
- Review Monthly Cost and Annual Cost to understand the total operating expense of your grow room.
- Use the Daily kWh figure to compare different lighting setups or identify energy-saving opportunities.
How the result changes with Electricity Rate
| Electricity Rate | Monthly Cost | Annual Cost |
|---|---|---|
| 0.07 | $17.08 | $204.96 |
| 0.1 | $25.62 | $307.44 |
| 0.2 | $51.25 | $615.00 |
| 0.33 | $85.41 | $1,024.92 |
What each input means
- Light Wattage
- Total wattage of all grow lights (e.g., 400W HPS or 240W LED).
- Light Hours per Day
- Hours lights are on per day (veg: 18, flower: 12).
- Fan Wattage
- Total wattage of inline and oscillating fans (run 24/7).
- Pump Wattage
- Water/air pump wattage if using hydroponics (0 for soil grows).
- Electricity Rate
- Your cost per kilowatt-hour from your utility bill.
How this is calculated
Worked example, using the default values
- Identify Input Parameters5 parametersLight Wattage = 400, Light Hours per Day = 18, Fan Wattage = 50, Pump Wattage = 15, Electricity Rate = 0.13 = 5 input(s) provided
- Calculate Monthly CostMonthly Cost34.16 = $34.16
- Calculate Daily UsageDaily Usage8.76 = 8.76
- Calculate Monthly UsageMonthly Usage262.8 = 262.8
Engine last updated . Checked against 1 independently-derived test — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why do fans and pumps cost more relative to their wattage than the lights do?
Fans and pumps are modeled as running the full 24 hours a day, while lights only run for the Light Hours per Day you enter (commonly 12-18 hours). A 50W fan running 24 hours draws 1.2 kWh/day, while a 50W light running only 12 hours draws just 0.6 kWh/day — the same wattage but double the energy use, because the fan's assumed runtime is longer.
How much does switching from an 18-hour to a 12-hour light schedule save?
At the default 400W light wattage, cutting Light Hours per Day from 18 to 12 lowers the light's own daily draw from 7.2 kWh to 4.8 kWh — a 2.4 kWh/day reduction that carries straight through Monthly Usage (x30) and Monthly Cost (x your electricity rate), since fan and pump draw are unaffected by the light schedule and stay exactly the same.
Does raising the electricity rate change how much energy the grow room uses?
No — Electricity Rate only affects Monthly Cost and Annual Cost, which are Monthly Usage multiplied by the rate. Daily Usage and Monthly Usage (measured in kWh) depend only on Light Wattage, Light Hours per Day, Fan Wattage, and Pump Wattage; the electricity rate never changes how much power the equipment actually draws, only what that power costs.
Is Monthly Usage based on the exact number of days in a given month?
No — Monthly Usage is calculated as Daily Usage times a flat 30 days, regardless of whether the actual month has 28, 30, or 31 days. This keeps the estimate simple and consistent for comparison purposes, but means the true kWh for a 31-day month will run slightly higher than what's shown here, and a 28-day month slightly lower.
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