Hydroponic Nutrients

Dosing Nutrient Concentrate and Converting EC to PPM

Nutrient dosing is a hydroponic nutrient concentrate’s own label rate scaled by your reservoir’s real water volume, and EC-to-PPM conversion is an EC reading multiplied by whichever of the two widely-used scale conventions your meter or guide assumes. Pick the mode that matches what you’re trying to figure out.

Nutrient dosing: every hydroponic nutrient concentrate’s label gives a dosage rate, such as “5 ml per gallon.” Enter that rate along with your reservoir’s actual water volume, and this calculator multiplies the two to tell you exactly how much concentrate to pour in.

EC ↔ PPM conversion: growers commonly measure a nutrient solution’s strength with an EC (electrical conductivity) meter, in mS/cm, but a lot of feeding-schedule guidance is written in PPM (parts per million) instead. Converting between the two isn’t as simple as it sounds, though — there are two different, both widely-used conversion conventions, and the same EC reading converts to a different PPM number depending on which one applies.

The Formula

Nutrient dosing:

$$\vA{\text{Concentrate Needed}} = \vB{\text{Dosage Rate}} \times \frac{\vC{\text{Reservoir Volume}}}{\text{Rate's Basis Volume}}$$

EC ↔ PPM conversion, using whichever scale your meter/guide assumes:

$$\text{PPM} = \text{EC (mS/cm)} \times \text{Scale (500 or 700)}$$

Two different conversion scales are both in widespread real-world use, so neither is “more correct” than the other — they’re simply different conventions:

An EC reading of 1.5 mS/cm therefore converts to 750 PPM on the 500 scale, but 1,050 PPM on the 700 scale — the same measurement, two genuinely different numbers depending on which scale you use.

Worked Example

Nutrient dosing: a 10-gallon reservoir, with a concentrate labeled 5 ml per gallon:

1. Concentrate needed: $\vA{5 \text{ ml/gal} \times 10 \text{ gal} = 50 \text{ ml}}$

EC to PPM conversion: an EC reading of 1.5 mS/cm, on the 500 scale:

1. PPM: $1.5 \times 500 = 750 \text{ PPM}$

If a feeding guide instead assumed the 700 scale for that same 1.5 mS/cm reading, it would read as 1,050 PPM instead — always check which convention a given source uses before comparing numbers.

For scaling how much fertilizer to apply to soil rather than a hydroponic reservoir, see the

Lawn Fertilizer Calculator Calculator instead.

Key Factors to Consider

• Target EC/PPM strength varies significantly by plant type and growth stage. Seedlings and young plants typically need a much weaker nutrient solution than mature, fruiting plants — always check your specific crop’s own feeding chart for the target strength at its current growth stage, rather than assuming one universal target.
• Water temperature and quality affect a reservoir beyond just nutrient concentration. Reservoir temperature, pH, and dissolved oxygen all interact with nutrient uptake — getting the nutrient dosage right is necessary but not sufficient on its own for healthy plant growth in a hydroponic system.
• EC meters need periodic calibration to stay accurate. Like any measurement instrument, an EC meter’s readings can drift over time — regular calibration against a known reference solution keeps your EC (and therefore PPM) readings trustworthy.
• Multi-part nutrient systems (Grow, Micro, Bloom, etc.) each have their own dosage rate, usually added in the same base ratio. Many hydroponic nutrient lines use multiple concentrate bottles mixed together at specified ratios — run this calculator once per bottle at its own label rate for a complete, correctly balanced mix.

Common Mistakes

• Assuming the 500 scale and 700 scale give the same PPM number. They don’t — the same EC reading converts to genuinely different PPM values depending on the scale, so a “target PPM” from one source can be wrong by 40% if applied against the other scale.
• Mixing up your reservoir’s volume units with the label’s dosage units. A rate given in “ml per gallon” needs a reservoir volume in gallons, not liters — convert first or let this calculator handle the conversion rather than multiplying mismatched units directly.
• Adding concentrate for the reservoir’s full capacity instead of its actual water level. A partially filled reservoir needs proportionally less concentrate — dose based on how much water is actually in the tank, not the tank’s maximum size.
• Ignoring calibration drift on an EC meter. A meter that hasn’t been calibrated in a while can read consistently off, making every dose calculated from it wrong by the same margin.

Useful to Know

• Scaling fertilizer for soil-based garden beds instead of a hydroponic reservoir? The Raised Garden Bed Soil Calculator calculator handles soil volume and amendment quantities.
• Want to know how far apart to space plants once your nutrient mix is dialed in? The Plant Spacing Calculator calculator estimates spacing for your specific crop.
• Composting instead of a bottled concentrate? The Compost C:N Ratio Calculator calculator balances carbon and nitrogen inputs for a healthy compost pile.