Nutrient Schedule Calculator
Feed concentration by growth stage and medium.
About this calculator
This calculator translates a cannabis plant's growth stage into a concrete feeding target: a PPM (parts per million of dissolved nutrient solids) or EC (electrical conductivity, in mS/cm) number to mix to, plus how much concentrated nutrient that requires. Each of the six stages from seedling through the pre-harvest flush carries its own baseline PPM midpoint (275 for seedlings up to 1400 at mid-flower, dropping back toward zero during flush to purge built-up salts) and its own relative nitrogen-phosphorus-potassium emphasis — heavy nitrogen early for foliage growth, shifting to phosphorus and potassium in flower to support bud development. Your chosen nutrient-strength percentage scales that stage baseline up or down (useful for sensitive strains or aggressive feeders), and the calculator subtracts your tap water's existing PPM baseline so you're not double-counting dissolved solids already in the water before nutrients go in. EC is derived from PPM using a standard 500-scale conversion (EC = PPM ÷ 500), matching how most consumer TDS/EC meters are calibrated.
Concentrate volume assumes a typical 3-part nutrient line dosed at 5 mL per gallon to hit 1000 PPM, scaled linearly to your actual target. Reservoir life is estimated from a per-plant daily water-use figure that varies by stage, letting you plan refill timing. Because real nutrient uptake varies by strain, root zone temperature, and pH, use these numbers as a starting recipe and adjust based on runoff PPM and plant response rather than following the schedule blindly.
Inputs
Results
Target PPM
1,000
How to Use This Calculator
- Select the current growth stage (seedling through flush).
- Enter reservoir size in gallons, nutrient strength (%), tap water PPM baseline, and plant count.
- Review Target PPM, Target EC (mS/cm), Concentrate (mL/gal), and Reservoir Life (days).
- Check N, P, and K ratio outputs to confirm they match stage-appropriate emphasis.
How the result changes with Nutrient strength (%)
| Nutrient strength (%) | Target PPM |
|---|---|
| 50 | 500 |
| 75 | 750 |
| 150 | 1,500 |
What each input means
- Growth stage
- Sets target PPM/EC and N-P-K emphasis for this stage.
- Reservoir size (gal)
- Reservoir or feed tank capacity in US gallons.
- Nutrient strength (%)
- Percentage of recommended nutrient concentration (reduce for sensitive strains).
- Tap water PPM
- Dissolved solids in your water before adding nutrients (TDS reading).
- Number of plants
- Plants feeding from this reservoir.
What each result means
- Target PPM
- Final target PPM for the nutrient solution.
- PPM to add
- PPM of nutrients to add above baseline water.
- Target EC (mS/cm)
- Equivalent electrical conductivity.
- Concentrate (mL/gal)
- Milliliters of concentrate per gallon of water.
- Total concentrate (mL)
- Total mL of concentrate for the full reservoir.
- Reservoir life (days)
- Days before the reservoir is depleted.
- Daily water use (gal)
- Estimated daily water consumption by plants.
- N ratio (%)
- Relative nitrogen emphasis for this stage.
- P ratio (%)
- Relative phosphorus emphasis for this stage.
- K ratio (%)
- Relative potassium emphasis for this stage.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersGrowth stage (0-5) = 2, Reservoir size (gal) = 20, Nutrient strength (%) = 100, Tap water PPM = 50 = 5 input(s) provided
- Calculate Target PPMTarget PPM = round(basePpmTarget * (nutrientStrengthPct / 100))1000 = 1000
- Calculate PPM to addPPM to add950 = 950
- Calculate Target ECTarget EC2 = 2
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 does the target PPM drop back down during the flush stage instead of continuing to climb?
Flush is stage 5 in the calculator, with a baseline PPM target of just 200 (versus 1400 at mid-flower), because the purpose of flushing is to purge built-up salts from the growing medium before harvest rather than feed the plant further. The N-P-K ratio for flush is also zeroed out entirely (0-0-0), reflecting that you're feeding plain, low-PPM water at this stage rather than a nutrient mix.
How exactly does the calculator convert my target PPM into an EC reading?
It divides the adjusted PPM target by 500 to get EC in mS/cm — a standard 500-scale conversion that matches how most consumer TDS/EC meters are calibrated. If your meter uses a different conversion scale (like the 700-scale used by some brands), the EC number this calculator reports won't line up with your meter's reading even though the underlying PPM target is the same.
Why does the calculator subtract my tap water PPM from the stage target instead of ignoring it?
The 'PPM to add' output is your stage's adjusted target minus your entered tap water baseline, because whatever dissolved solids are already in your source water count toward your total feed strength once nutrients are mixed in. Skipping this step would mean systematically over-feeding relative to your target, especially with hard tap water that already carries 200+ PPM before any nutrients are added.
Why do nitrogen, phosphorus, and potassium ratios flip between veg and flower stages?
Each stage carries its own relative N-P-K parts — seedling and early veg lean 3:1:2 favoring nitrogen for foliage growth, while mid-flower shifts to 1:3:4 favoring phosphorus and potassium to support bud development. The calculator converts these relative parts into percentages of the total, so the ratio output changes stage to stage even if you don't touch the reservoir size or nutrient strength inputs.
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