Indoor Herb Garden Calculator
Plan a kitchen herb garden with container counts, supplemental lighting, and watering schedules.
About this calculator
Containers Needed depends on exactly one input: Herb Varieties. Each variety gets its own pot, so the count is simply your variety count rounded up — Window Light Hours and Container Diameter have no effect on this figure at all. Supplemental Light Wattage instead sizes a grow light to physically cover the total footprint of all your pots, using Container Diameter and Herb Varieties to compute that footprint; it does not scale down based on how much natural window light you already receive, since the calculator sizes the fixture for the full tray rather than calculating a marginal top-up wattage. Window Light Hours works differently: it flows entirely into Est. Monthly Cost and Needs Supplement rather than into the wattage figure. Because the model treats 8 hours of daily window light as "fully lit," Est.
Monthly Cost stops falling once Window Light Hours reaches 8 — pushing it higher than 8 saves nothing further in this model, since the light-deficit term the cost calculation uses is floored at zero. Below that threshold, more window light steadily lowers the estimated electricity cost — but only when Supplement Light is set to Yes. If Supplement Light is set to No, Supplemental Light Wattage is always 0, so there is no electricity cost to lower and Est. Monthly Cost stays flat at the $3/month fertilizer baseline no matter how many Window Light Hours you enter. This tool assumes one fixed grow-light wattage rate and a flat $3/month fertilizer estimate; it does not account for herb species with very different light or water needs (basil and rosemary, for example, have quite different care requirements) grouped together in the same count.
Inputs
Results
Containers Needed
5
Est. Monthly Cost
$3.39
How to Use This Calculator
- Enter the number of herb varieties you want to grow (basil, parsley, cilantro, mint, thyme, etc.).
- Enter the daily hours of direct sunlight your window receives and whether you plan to use a supplemental grow light.
- Enter the container diameter in inches — most herbs thrive in 6–8 inch pots.
- Review Containers Needed and Supplemental Light Wattage to plan your setup.
- Note Water Every (days) and Est. Monthly Cost to establish a care routine and budget.
How the result changes with Herb Varieties
| Herb Varieties | Containers Needed | Est. Monthly Cost |
|---|---|---|
| 2.5 | 3 | $3.23 |
| 3.75 | 4 | $3.31 |
| 7.5 | 8 | $3.62 |
| 13 | 13 | $4.00 |
What each input means
- Herb Varieties
- Number of different herbs (basil, parsley, cilantro, etc.).
- Window Light Hours
- Hours of direct sunlight your window receives daily.
- Supplement Light
- Whether you will use a grow light to supplement natural light.
- Container Diameter
- Pot diameter in inches — most herbs do well in 6-8" pots.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersHerb Varieties = 5, Window Light Hours = 4, Supplement Light = 1, Container Diameter = 6 = 4 input(s) provided
- Calculate Containers NeededContainers Needed5 = 5
- Calculate Supplemental Light WattageSupplemental Light Wattage25 = 25
- Calculate Water EveryWater Every3 = 3
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why doesn't Container Diameter change Containers Needed?
Containers Needed counts one pot per herb variety, driven entirely by Herb Varieties. Container Diameter instead affects Supplemental Light Wattage (a bigger pot footprint needs more light to cover) and Water Every (days), but it never changes how many containers the calculator recommends.
Why doesn't more Window Light Hours reduce my Supplemental Light Wattage?
Supplemental Light Wattage is sized to cover the full footprint of your pots, computed from Container Diameter and Herb Varieties — it represents the fixture size needed to light the tray on its own, not a marginal top-up on top of existing window light. Window Light Hours instead affects Est. Monthly Cost and Needs Supplement, since those track how many hours the light actually needs to run.
Does getting more than 8 hours of window light keep lowering my Est. Monthly Cost?
No. The calculator treats 8 hours of daily window light as fully meeting most herbs' light needs, so the cost calculation's light-deficit term bottoms out at zero once Window Light Hours reaches 8. Increasing it further leaves Est. Monthly Cost unchanged, settling at the flat baseline fertilizer cost with no electricity cost added.
If I set Supplement Light to No, does Window Light Hours still change my Est. Monthly Cost?
No. Est. Monthly Cost only includes electricity when Supplement Light is set to Yes, because Supplemental Light Wattage is always 0 when Supplement Light is No — there is no light running, so there is no electricity cost for Window Light Hours to affect. In that case Est. Monthly Cost stays flat at the $3/month fertilizer baseline regardless of how many Window Light Hours you enter.
Does this calculator account for different herbs needing different amounts of light or water?
No. It treats every herb variety identically for lighting and watering purposes, using one container size, one grow-light wattage rate, and one watering-frequency formula across the whole garden. In reality, herbs like basil and rosemary have quite different light and water preferences, so treat container size and watering frequency as starting points to adjust per plant rather than a precise per-species schedule.
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