Free Grow Calculators for Growing Cannabis
VPD, pH, EC, light levels and more — real numbers instead of guesswork. Right in your browser, no sign-up.
Numbers, not gut feeling
Climate, water and light can all be measured — but readings alone don’t help much if you don’t know what they mean or what to do next. Our grow calculators turn your readings straight into a clear recommendation, each with a short explanation of why that value matters.
Each grow calculator covers one specific decision: the VPD (vapor pressure deficit) calculator tells you whether your climate is in the right range, the pH and EC calculators help you dose your nutrients, the PPFD (photosynthetic photon flux density) and DLI (daily light integral) calculators show whether your lighting is really enough, and the harvest time and watering calculators take the guesswork out of two of the most common beginner questions.
A reading on its own doesn’t tell you much if you don’t know whether it’s too high, too low or just right — and even less about what you should actually do. Our calculators close exactly that gap: you enter your measured values and instantly get a clear assessment plus a recommendation, instead of digging through charts yourself.
All grow calculators are completely free, run right in your browser and don’t require a sign-up. For deeper explanations of the individual values, it’s also worth checking out our Knowledge Base or going straight to the Climate hub.
These calculators don’t replace a feel for your plant, but they take the guesswork out of the numbers — we use them ourselves before touching any dials.
Which grow calculator do you need right now?
VPD Calculator
Calculate the ideal vapor pressure deficit (temperature + humidity) for the vegetative and flowering stages.
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pH Calculator
How much pH Down or pH Up you need to add to your water to hit your target.
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EC Calculator
Dilute or strengthen your nutrient solution to match the growth stage.
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DLI Calculator
Calculate your plant’s total daily light — from light intensity and hours of light.
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PPFD Calculator
Find the light intensity at the canopy — for the right light-to-plant distance.
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Harvest Time Calculator
Estimate the ideal harvest window from flowering start, the strain’s flowering time and trichome stage.
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Watering Calculator
The right amount of water per watering for your pot size — to prevent overwatering and underwatering.
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Grow Light Electricity Cost Calculator
What your grow costs in electricity – split into veg and flower, including exhaust and fans.
Calculate now →Frequently asked questions about the grow calculators
Which calculator matters most for growing cannabis?
The VPD calculator is especially valuable because it combines temperature and humidity into a single, meaningful climate value. The pH calculator is just as essential, since the wrong pH is the most common cause of nutrient problems.
Are the calculators really free to use?
Yes, all 8 calculators are completely free, run right in your browser and don’t require a sign-up or registration.
How accurate are the calculators?
The calculators are based on established formulas and guideline values from real-world cannabis growing (e.g. the Magnus formula for VPD). They give you reliable guidance, but they don’t replace watching your own plant closely.
What’s the difference between the PPFD and DLI calculators?
PPFD measures light intensity at a single moment (a snapshot), while DLI accounts for the total amount of light over the whole day. Together they give you a complete picture of your lighting.
Do I need any prior knowledge to use the calculators?
No, each calculator briefly explains what the result means and what you should do with it. All you need to enter are your measured values (e.g. temperature, humidity or light wattage).
Which calculators are currently available on PlantClue?
There are currently 8 calculators: VPD, pH, EC, DLI, PPFD, harvest time, watering and grow light electricity cost — each built for a specific decision when growing cannabis.
