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Hydroponic nutrient calculator: EC, ppm and dose
Pick a crop to get its target EC, ppm and pH for each growth stage, convert between meter scales, and work out how many millilitres to add — or how much water to dilute with.
1. Feed plan and nutrient dose
Target EC by crop and stage, with your source water subtracted — the same targets the Anyponics app uses.
Use the dose rate from my nutrient bottle
2. EC to ppm converter
Type into any box. ppm (TDS) meters measure EC and multiply by a fixed scale, so the same solution reads differently on different pens.
1 mS/cm = 1 dS/m = 1,000 µS/cm. "CF" (used in some older UK and Australian guides) is EC × 10.
3. Top up or dilute a reservoir
Your reservoir has dropped or drifted. Enter what it reads now and the calculator tells you how much water and nutrient gets it back to target.
Reading in ppm? Convert it in box 2 first.
Calibrate to my nutrient (optional)
The default assumes a typical 3-part concentrate raises EC about 0.11 mS/cm per mL per US gallon. Next time you mix, note the numbers here and the mL figures below become specific to your bottle.
Volume for calibration = Full volume above.
pH: what the calculator won't pretend to know
Target pH 5.8–6.2 for hydroponics, 6.8–7.0 for aquaponics, and 6.0–6.5 for microgreens on plain water. Above roughly 6.5 in hydroponics, iron, manganese and phosphorus become less available first — you see deficiency symptoms in a reservoir full of food.
What this page deliberately does not do is tell you how many millilitres of pH Down to add. That depends on your water's alkalinity — the bicarbonate that buffers it — not on the pH reading. Two waters can both read pH 7.6 and need very different amounts of acid. Oklahoma State Extension notes that water above about 75 ppm alkalinity pushes nutrient-solution pH up and needs checking more often. Any tool that gives you a precise pH Down volume from a pH reading alone is guessing.
A method that works on any water:
- Mix nutrients to your target EC first — the concentrate itself shifts pH.
- Add a small amount of pH Down (a fraction of a millilitre for a small reservoir), stir or run the pump, and wait 15 minutes.
- Re-measure. Repeat with smaller additions as you approach the target. Never chase pH back and forth with Up and Down.
- Write down the total. Next time, start with about three-quarters of it — that number is now reliable for your water and your nutrient.
If you are adding a lot of acid every time, reverse-osmosis or rainwater (or a blend) removes most of the alkalinity and makes pH far more stable.
Hydroponic ppm chart by crop
The full-strength range for each crop — the same targets the calculator above and the Anyponics app use. Seedlings start at about half the low end; leafy crops stay at the vegetative figure until harvest; fruiting crops step up to the top of the range once fruit sets.
| Crop | EC (mS/cm) | ppm (500 scale) | ppm (700 scale) | pH |
|---|---|---|---|---|
| Lettuce & leafy greens | 0.8 – 1.4 | 400 – 700 | 560 – 980 | 5.8 – 6.2 |
| Basil & herbs | 1.0 – 1.6 | 500 – 800 | 700 – 1,120 | 5.8 – 6.2 |
| Strawberries | 1.2 – 2.0 | 600 – 1,000 | 840 – 1,400 | 5.8 – 6.2 |
| Cucumbers | 1.8 – 2.5 | 900 – 1,250 | 1,260 – 1,750 | 5.8 – 6.2 |
| Peppers | 1.8 – 2.8 | 900 – 1,400 | 1,260 – 1,960 | 5.8 – 6.2 |
| Tomatoes | 2.0 – 3.5 | 1,000 – 1,750 | 1,400 – 2,450 | 5.8 – 6.2 |
| Microgreens | 0 – 0.8 | 0 – 400 | 0 – 560 | 6.0 – 6.5 |
Multiply by 640 instead of 500 or 700 if your meter uses that scale.
What published sources say
Extension figures differ from each other more than most charts admit — they come from different cultivars, water, light levels and growing systems. Use them as a sanity check, not a rule.
| Crop | Oklahoma State HLA-6722 (EC · pH) | This calculator |
|---|---|---|
| Lettuce | 1.2–1.8 · 6.0–7.0 | 0.8–1.4 · 5.8–6.2 |
| Spinach | 1.8–2.3 · 6.0–7.0 | 0.8–1.4 · 5.8–6.2 |
| Basil | 1.0–1.6 · 5.5–6.0 | 1.0–1.6 · 5.8–6.2 |
| Strawberry | 1.8–2.2 · 6.0 | 1.2–2.0 · 5.8–6.2 |
| Cucumber | 1.7–2.0 · 5.0–5.5 | 1.8–2.5 · 5.8–6.2 |
| Peppers | 0.8–1.8 · 5.5–6.0 | 1.8–2.8 · 5.8–6.2 |
| Tomato | 2.0–4.0 · 6.0–6.5 | 2.0–3.5 · 5.8–6.2 |
For lettuce specifically, long-running research by A.J. Both (Rutgers) held hydroponic lettuce at EC 1.15–1.25 mS/cm and pH 5.6–6.0 on reverse-osmosis water — inside the range above. The biggest disagreements are peppers (Oklahoma State is lower) and spinach (Oklahoma State is higher). If leaves show tip burn, come down; if growth is pale and slow with pH in range, go up a step.
How the numbers are worked out
- Stage targets. Seedling = the larger of half the crop's low EC or source water + 0.2. Vegetative = 60% of the way from the low to the high end. Flower and fruit = the high end (fruiting crops only).
- Subtract your water. EC to add = target − source-water EC. If you target 1.4 on tap water reading 0.3, you add 1.1, not 1.4.
- Starting dose. mL per gallon = EC to add ÷ 0.11, rounded — a typical 3-part concentrate. Brands vary by ±10% or more, so mix to the meter, not the number.
- ppm. ppm = EC × scale (500, 640 or 700). EC = ppm ÷ scale.
- Dilution. Water to add = volume × (EC now − target) ÷ (target − water EC). If that overflows the tank, drain first: drain = volume − full × (target − water EC) ÷ (EC now − water EC), then refill.
- Top-up. EC after filling with water = (EC now × volume + water EC × added water) ÷ full volume; nutrient then makes up the gap.
Mixing is treated as linear by volume, which is close enough for top-ups but not exact. Always finish with a meter reading. For a full walk-through of feeding by stage, see the hydroponic nutrient schedule.
Questions
How do I convert EC to ppm?
Multiply EC in mS/cm by your meter's scale: 500, 640 or 700. An EC of 1.4 reads 700 ppm on a 500-scale pen and 980 ppm on a 700-scale pen. To go from ppm back to EC, divide by the same number. A ppm figure is only meaningful if you know which scale produced it.
Which ppm scale does my meter use?
Check the manual or the packaging. Most inexpensive pens sold in North America use the 500 scale; the 700 scale is common in the UK and Australia; some meters use 640. If you can't find it, measure a 1.41 mS/cm calibration solution: about 705 ppm means 500 scale, about 990 ppm means 700 scale.
How much nutrient should I add to my reservoir?
Mix to a target EC, not to a millilitre figure. Subtract the EC of your source water from the target, then add concentrate a little at a time until the meter reads the target. As a starting point, a typical three-part concentrate raises EC by roughly 0.11 mS/cm per mL per US gallon, so raising 10 gallons by 1.0 mS/cm takes about 90 mL. Brands differ, so always measure.
What EC and pH should lettuce be grown at?
This calculator targets 0.8 to 1.4 mS/cm for lettuce (about 400 to 700 ppm on the 500 scale) and pH 5.8 to 6.2. Published figures vary: Rutgers research held lettuce at 1.15 to 1.25 mS/cm and pH 5.6 to 6.0 on RO water, and Oklahoma State lists 1.2 to 1.8 mS/cm. Start in the middle and watch for tipburn if you push higher.
How much pH down do I need?
No calculator can tell you honestly, because it depends on your water's alkalinity (its bicarbonate content), not on the pH reading. Hard water with high alkalinity can take many times more acid than soft or RO water to move the same distance. Add a small amount, stir, wait 15 minutes, re-measure, and note what it took. That figure is reliable for your water from then on.
Should I add hydroponic nutrient to an aquaponic system?
No. In aquaponics the fish feed is the nutrient source, and a hydroponic base pushes dissolved salts past what the fish tolerate. Run pH 6.8 to 7.0 and supplement only what fish waste is short of: chelated iron, potassium and calcium.