Growing plants indoors means working with variables that are hard to judge by eye — light levels, nutrient concentrations, seasonal changes. These free calculators and quizzes are built on real growing science, calibrated for northern European conditions, so you can make decisions based on data rather than guesswork.
Do I Need a Grow Light? Room Quiz
Answer five questions about your room — window direction, distance from the glass, season, and any obstructions outside — and the quiz estimates the Daily Light Integral (DLI) your space can deliver. It then compares that against the known light requirements for your chosen plant category and tells you clearly whether natural light is enough, marginal, or insufficient. The logic is calibrated for 59°N latitude, where winter light levels are dramatically lower than most guides assume.
This tool answers:
- Does my south, east, west, or north window provide enough light for what I want to grow?
- How much does distance from the window actually affect my plants?
- Can I grow herbs or fruiting crops through a northern European winter without artificial light?
- If I do need a grow light, what kind should I be looking for?
DLI Calculator
DLI — Daily Light Integral — is the total amount of photosynthetically useful light a plant surface receives in a day, measured in mol/m²/day. It is the metric that actually drives plant growth, and it is what separates a setup that works from one that leaves plants stalling. This calculator lets you input your light source specifications and photoperiod to find the DLI your plants are receiving, then compare it against research-backed targets for different crop types.
This tool answers:
- What DLI does my grow light deliver at a given mounting height and run time?
- How many hours per day should I run my grow light for herbs, leafy greens, or fruiting crops?
- Is my current lighting setup actually meeting my plants’ needs, or just keeping them alive?
- How do I combine natural window light with supplemental lighting effectively?
EC & Nutrient Calculator
Electrical conductivity (EC) measures how much dissolved nutrient is in your water. Get it too low and plants underperform; too high and you risk nutrient burn or salt stress. This calculator helps you find the right EC target for your plant type and growth stage, then work out the correct nutrient dose for your reservoir volume. It accounts for your tap water’s baseline EC so you are dosing accurately rather than guessing.
This tool answers:
- What EC level should my nutrient solution be at for seedlings, vegetative growth, or fruiting?
- How much nutrient concentrate should I add to my specific reservoir size?
- My tap water already has some EC — how do I account for that in my dosing?
- Why are my plants showing slow growth or yellowing even though I am adding nutrients?
Not sure where to start?
If you are new to indoor gardening, the Room Quiz is the best first step — it tells you immediately whether your space needs a grow light before you invest in anything else.
