Grow Calculator
Nutrient & Feed Calculator
Stop guessing at feed strength. Get the target PPM and EC for your stage, how much of that is actually fertilizer, and exactly how much solution to mix.
800–1100 ppm
target for late veg (week 5-6)
1.60–2.20 EC
same target in mS/cm
+740–1040 ppm
actual fertilizer to add over your source water
4.4 gal (16.7 L)
total to mix — 1.1 gal per plant
Mix to roughly 950 ppm on the 500 (Hanna / TDS 0.5) scale, then pH to 6.2-6.5 in soil or 5.8-6.2 in coco and hydro. That reading equals 1330 ppm on a 700-scale meter — the most common source of feeding confusion.
Feed strength is a range, not a number
Every strain and every environment tolerates a different feed. Start at the low end of the range for your stage and climb only if the plant asks for it — pale, light-green new growth and slow development mean it wants more. Crispy brown leaf tips mean you already went too far.
Always subtract your source water
Reverse osmosis water starts near 0 ppm, so your whole reading is fertilizer. City water often starts at 150-400 ppm and well water can be much higher. Those dissolved solids count toward your total EC even though a lot of them are not usable nutrition.
Water to runoff
Feeding to 10-20% runoff flushes accumulated salts out of the root zone and keeps EC from climbing in the medium. If you never see runoff, salts build up until the plant locks out and shows what looks like a deficiency but is really an excess.
Common questions
- How much nutrient solution should I give per watering?
- Water to 10-20% runoff. In practice that means roughly 20-25% of your container volume per feed for soil and coco. A 5-gallon fabric pot typically takes about 1 to 1.25 gallons.
- What PPM should cannabis be fed at?
- Roughly 200-400 ppm for seedlings, 500-800 in early veg, 800-1100 in late veg, 1000-1400 in flower, and plain pH'd water for the final one to two weeks. These are on the 500 scale and always include your source water's starting PPM.
- Why do EC and PPM readings disagree between meters?
- There is no single PPM standard. Meters convert from EC using a 500, 640, or 700 multiplier depending on brand. A 1.4 EC solution reads 700 ppm on a Hanna and 980 ppm on a Bluelab. Always state which scale you mean, or just talk in EC.
- Should I subtract my tap water PPM?
- Track both. If your tap starts at 250 ppm, a 1000 ppm target means you are only adding 750 ppm of actual fertilizer, and the rest is calcium and magnesium carbonates that may or may not be plant-available. Growers on hard water usually skip Cal-Mag entirely.