Hydroponics Nutrient Solution Calculator
Calculate how much nutrient concentrate to add to reach your target EC.
Includes ppm conversion and EC guidance for different plant stages.
In hydroponics, plants receive all their nutrients dissolved in water. The electrical conductivity (EC) of the nutrient solution tells you how concentrated the nutrients are. Too little and plants starve; too much and they suffer from nutrient burn.
Formula:
Concentrate volume (mL) = (Target EC − Water EC) / Concentrate EC per mL/L × Reservoir volume (L)
EC (Electrical Conductivity): EC is measured in mS/cm (millisiemens per centimeter) or µS/cm. 1 mS/cm = 1000 µS/cm. Pure water has an EC near 0. Tap water typically reads 0.1–0.5 mS/cm. A strong nutrient solution reads 2.0–3.5 mS/cm.
PPM conversion: EC can also be expressed as ppm (parts per million) of dissolved solids. Two conversion standards exist:
- 500 scale (US): ppm = EC (mS/cm) × 500
- 700 scale (European/Hanna): ppm = EC (mS/cm) × 700
This calculator uses the 500 scale (most common in the US).
Typical EC targets by growth stage:
| Stage | EC (mS/cm) | ppm (500 scale) |
|---|---|---|
| Seedlings / clones | 0.8 – 1.2 | 400 – 600 |
| Vegetative growth | 1.2 – 2.0 | 600 – 1,000 |
| Early flowering | 1.8 – 2.5 | 900 – 1,250 |
| Peak flowering / fruiting | 2.0 – 3.5 | 1,000 – 1,750 |
| Late fruiting / flush | 0.5 – 1.0 | 250 – 500 |
Common concentrate strengths:
This is the number people get wrong, and getting it wrong by a factor of ten is easy because the units are awkward. The figure you want is how much EC one millilitre of concentrate per litre of water actually adds, and for ordinary two-part and three-part liquid concentrates that is around 0.3 mS/cm per mL/L, not 2 or 3.
| Product | mS/cm per mL/L | To reach EC 1.0 above your water |
|---|---|---|
| General Hydroponics Flora Series (3-part combined) | ~0.27 | ~3.7 mL/L |
| Canna Aqua Vega A+B (combined) | ~0.32 | ~3.1 mL/L |
| Typical 2-part concentrate | 0.25–0.35 | 3–4 mL/L |
Sanity-check any figure against the label. GH Flora at an aggressive vegetative dose is roughly 8 mL per litre in total across the three bottles, and that lands near EC 2.0. If a number tells you a single millilitre per litre gets you to EC 2.5, it is out by roughly ten times and will leave your plants starving on a solution barely stronger than tap water.
Dry salt fertilisers behave differently and are usually dosed by weight rather than volume, so this field does not apply to them.
pH reminder: EC tells you nutrient concentration, but pH controls whether the plant can take it up. Always adjust EC first, then check and adjust pH.
- Soil / coco: pH 6.0 – 6.5
- Deep Water Culture / NFT / Aeroponic: pH 5.5 – 6.0
Important: Always mix nutrients into water, never water into nutrients. Start with a clean reservoir, add your base water, then add nutrients while stirring.
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