Hydroponic PPM & EC NPK Nutrient Solution Dilution Calculator
Getting nutrient strength right is the difference between vigorous hydroponic growth and nutrient burn or deficiency. This calculator takes your reservoir's current PPM, a crop-specific or custom target, and your stock solution's strength to tell you exactly how much concentrate to dose, plus the equivalent EC reading.
Add about 130.0 g of concentrated nutrient to your 20.0 L reservoir to raise PPM from 50 to 700.
| Metric | Value |
|---|---|
| Reservoir volume (L) | 20.0 |
| Current PPM | 50 |
| Target PPM | 700 |
| Delta PPM | 650 |
| Target EC (500 scale) | 1.40 |
| Nutrient to add | 130.0 g / ml |
| Final PPM | 700 |
Formula & step-by-step maths
- Factor
- Grams (or ml) of concentrate per litre needed to raise PPM by 100
- Litres
- Reservoir volume converted to litres
PPM, EC and TDS explained
PPM (parts per million) and EC (electrical conductivity) measure the same thing from different angles: EC measures how well the solution conducts electricity, and most consumer meters convert that to a PPM estimate using either a 500 or 700 scale. This tool uses the common 500 scale, so EC = PPM / 500.
Why crop targets differ so much
Leafy greens like lettuce are light feeders and stay healthiest around 560-840 ppm, while fruiting crops like tomatoes need heavier feeding, often 1050-1400 ppm during fruiting. Cannabis and herbs sit in between and shift across vegetative and flowering stages, so treat the presets as a starting midpoint, not a fixed target.
Reading your stock concentration factor
Nutrient labels vary widely; the 'g per litre per 100 ppm' factor tells the calculator how strong your particular concentrate is. If your label states a dose like '2 ml per litre raises EC by 0.4', convert that to a per-100-ppm factor (0.4 EC ≈ 200 ppm, so 2 ml per 200 ppm = 1 ml per 100 ppm) and enter it here.
Practical dosing tips
Always add nutrients gradually and re-measure with a calibrated PPM/EC meter rather than trusting a single calculation, since water source PPM and nutrient product strength both vary. Recheck after 15-30 minutes of circulation, as solids can take time to fully dissolve in cooler reservoirs.
Typical target PPM ranges by crop stage
| Crop | Seedling | Vegetative | Flowering/Fruiting |
|---|---|---|---|
| Lettuce & leafy greens | 400-500 | 560-840 | n/a |
| Tomato | 500-800 | 1000-1200 | 1200-1400 |
| Cannabis | 300-400 | 700-900 | 900-1100 |
| Herbs (basil, mint) | 400-600 | 700-900 | n/a |
| Strawberry | 560-700 | 800-1000 | 1000-1200 |
| Peppers | 600-800 | 1000-1200 | 1200-1450 |
People also ask
What's the difference between the 500 and 700 PPM scales?
Both convert EC to PPM but with different multipliers; a 700-scale meter will read about 40% higher than a 500-scale meter for the same EC. This calculator assumes the 500 scale, common in North American hydroponic meters.
How do I find my stock solution's concentration factor?
Check the manufacturer's dosing chart for how many ml or grams per litre raises EC or PPM by a known amount, then rescale that ratio to grams per litre per 100 ppm as described in the sections above.
Can I use this for soil fertigation instead of hydroponics?
The dilution math works the same way, but soil buffers nutrient availability differently than an inert hydroponic medium, so soil growers should generally target the lower end of any crop's PPM range.
Why is my final PPM different from what I measured?
Tap or well water often carries dissolved minerals beyond what a cheap meter reports, and different nutrient salts affect conductivity unevenly, so lab-calibrated dosing charts remain more precise than any single-formula estimate.
Should I zero out my meter before adding nutrients?
Always measure your current water PPM first and enter it as the current PPM input, since this tool calculates the delta needed rather than assuming your source water is at zero.
How often should I top up nutrients in a recirculating system?
Check PPM daily in active recirculating systems, since plants uptake water faster than nutrients, causing PPM to drift upward over the week even without adding more concentrate.
What happens if I add too much nutrient at once?
Overshooting PPM risks root burn and nutrient lockout; dilute the reservoir with plain water rather than trying to precisely reverse a dosing error.
Does temperature affect PPM readings?
Yes, most meters apply automatic temperature compensation, but readings taken far from 25°C/77°C reference temperature can drift; let solution reach room temperature before dosing decisions.
Can I use this calculator for multi-part nutrient systems (A+B)?
Yes, run the calculation once per part using each part's individual concentration factor, then add both amounts to the reservoir, keeping parts separate until fully diluted in water.
Is a higher PPM always better for faster growth?
No, exceeding a crop's tolerance range causes nutrient burn and reduced uptake; matching the crop-stage target closely produces healthier growth than maximizing PPM.
Three worked examples
Same engine, three different starting points — useful if you want to see how sensitive the answer is before you type your own numbers in.
Example 1: reservoir volume 15.6 L, volume unit "Litres"
On the lower / more conservative end. Add about 101.4 g of concentrated nutrient to your 15.6 L reservoir to raise PPM from 50 to 700.
Example 2: reservoir volume 20 L, volume unit "Litres"
A typical middle-of-the-road setup. Add about 130.0 g of concentrated nutrient to your 20.0 L reservoir to raise PPM from 50 to 700.
Example 3: reservoir volume 26 L, volume unit "Gallons"
On the higher / more demanding end. Add about 639.7 g of concentrated nutrient to your 98.4 L reservoir to raise PPM from 50 to 700.
Quick answers about the Hydroponic PPM & EC
What exactly does the Hydroponic PPM & EC work out?
Getting nutrient strength right is the difference between vigorous hydroponic growth and nutrient burn or deficiency. You enter reservoir volume, volume unit, current water PPM and crop preset (plus 2 more optional details) and the result panel updates straight away, so you can compare two or three versions of the same question in a few seconds.
What do I need before I start?
Only 6 fields: reservoir volume, volume unit, current water PPM, crop preset, target PPM (used if custom) and stock concentration factor. Nothing else is needed and nothing is stored.
How is it calculated — pPM, EC and TDS explained?
PPM (parts per million) and EC (electrical conductivity) measure the same thing from different angles: EC measures how well the solution conducts electricity, and most consumer meters convert that to a PPM estimate using either a 500 or 700 scale. The same maths runs inside this page, so hand-checking the result on paper gives you the identical figure.
Why do two calculators give me different answers for hydroponic PPM & EC?
Leafy greens like lettuce are light feeders and stay healthiest around 560-840 ppm, while fruiting crops like tomatoes need heavier feeding, often 1050-1400 ppm during fruiting. Different sites pick different assumptions, so always check which method a calculator states before you trust the gap between two numbers.
What does the "Typical target PPM ranges by crop stage" table on this page tell me?
It is the reference range this tool works against — 6 rows from "Lettuce & leafy greens" (400-500) up to "Peppers" (600-800). Use it to sanity-check whether the number you just calculated sits where you expected it to.
Which volume unit should I pick?
The dropdown offers 2 choices — Litres and Gallons. Pick the one that matches your real situation rather than the one you would like to be true; volume unit usually moves the final figure more than any other single input, so it is worth running it twice with the option above and below your guess.
Does it work in both metric and imperial (or another currency)?
Yes. The "Volume unit" control converts every field and every result, so you never have to convert anything by hand before typing it in. Switch it after entering your numbers and the output re-renders instantly in the new system.
Do I have to press a button or reload the page to see the result?
No. Hydroponic PPM & EC runs completely inside your browser, so the moment you change a value the cards recalculate — there is no submit step, no page reload and no waiting for a server round trip. That also means it keeps working on a weak or intermittent mobile connection.
Is it free, and do you keep what I type?
It is free with no sign-up, no app install and no usage limit. Nothing you enter into Hydroponic PPM & EC leaves your device — the calculation is JavaScript running locally, so there is no upload of your figures to DrHint or anyone else.
Can I use it on a phone?
Yes — the layout stacks to a single column on small screens and the number fields open the numeric keypad on both Android and iOS. Many people bookmark this page or add it to their home screen and re-open it whenever the question comes up.
Anything to be careful about with the result?
Both convert EC to PPM but with different multipliers; a 700-scale meter will read about 40% higher than a 500-scale meter for the same EC. Treat the output as a well-grounded estimate for planning, not as a professional, legal or medical decision on its own.
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