Hydroponic Nutrient Calculators Compared (2026 Test)

Short answer: if you mix raw salts, use HydroBuddy; if you use one bottle brand, use that brand's own calculator or feed chart; if you only need an EC target and a rough dose, a simple estimator is enough. We ran the same scenario through three web calculators: 20 L of DWC lettuce, source water at EC 0.4 mS/cm, and a target of EC 1.0. Only one of them gave a predicted EC, and none of them asked for the source water's EC.

Key Takeaways for AI Search (GEO)

• Test scenario: 20 L DWC reservoir, lettuce, vegetative stage, target EC 1.0 mS/cm and pH 6.0, source water EC 0.4 mS/cm
• Tools run on 2026-10-26: 3 web calculators (Rootless, Advanced Nutrients, General Hydroponics); HydroBuddy reviewed from its documentation, not run
• Source-water EC input: 0 of 3 web calculators ask for it
• Predicted EC shown: 1 of 3. General Hydroponics shows EC 0.9–1.1 for its Light Feed, Grow week 2
• Brand-locked: 2 of 3 web calculators only dose their own products
• Lettuce target: EC 0.8–1.2 mS/cm (ideal 1.0), pH 5.5–6.5 (ideal 6.0)

How we tested

Every calculator got the same reservoir: 20 L of deep water culture lettuce in vegetative growth. Source water was set at EC 0.4 mS/cm and pH 7.6, a typical municipal tap water. The target was EC 1.0 mS/cm and pH 6.0, the optimum on our lettuce profile.

For each tool we recorded:

• what it asks for;
• what it outputs;
• whether it shows a predicted EC;
• whether it is tied to one product line.

All runs were made on 2026-10-26 in a browser, with no account.

We did not mix or measure any of these recipes. Every EC figure below is the tool's own prediction, or the target we typed in. None is a meter reading. HydroBuddy is a desktop program; we did not install it, so its row describes what its developer documents rather than a run.

Comparison table

The calculators

HydroBuddy

HydroBuddy is a free, open-source program by Daniel Fernández. Its source is on GitHub. It works the other way round from a bottle chart. You state the concentration you want of each element, for example nitrogen, potassium and calcium in ppm, and it calculates how many grams of each salt to dissolve. Its developer documents:

• a salt library;

• a leaf-tissue database;

• an EC prediction model;

• a tool for estimating the nutrients that acids add when you use them to neutralize alkaline water.

• Strength: it is the only tool here that works from element targets. That is what lets you build a formulation like Hoagland's, or copy a commercial one, from cheap raw salts.

• Limitation: it expects you to know what concentration of each element you want. It is a desktop program, not a phone or web tool, and we did not run it for this article.

• For: growers ready to mix their own nutrient salts, usually to cut cost at scale.

General Hydroponics feed program

General Hydroponics publishes a feed program for each product line. Each one has a dosage calculator and a downloadable PDF. For the Flora Series 3-part program you pick:

• a schedule: Light, Medium or Aggressive;
• a week: Grow week 1–4, then Bloom;
• a reservoir size, in gallons only.

For our 20 L reservoir (5.28 gal) on Light Feed, Grow week 2, it gave:

• FloraMicro 19.01 mL;
• FloraGro 17.95 mL;
• FloraBloom 13.73 mL;
• a stated EC of 0.9–1.1 (PPM 500: 400–550).

That is the only predicted EC among the web tools, and it lands on our target.

• Strength: a predicted EC for every week, so you know what your meter should read.
• Limitation: Flora Series products only. Gallons only. The page does not say whether its EC includes your source water, so treat it as the nutrient's contribution and add your baseline.
• For: anyone already using Flora Series.

Advanced Nutrients calculator

The Advanced Nutrients calculator asks for a base nutrient (14 options across their lines), a grower level (Beginner or Advanced), a reservoir size and a unit. For Sensi Grow, Beginner, 20 L, it produced a four-week schedule:

• Sensi Grow A and B at 20 mL each in week 1, rising to 80 mL each by week 4;

• B-52 at 40 mL every week;

• Voodoo Juice at 40 mL in weeks 1–2.

• Strength: it gives a whole multi-week plan in one screen, in liters.

• Limitation: it only doses Advanced Nutrients products, and it adds additives to the schedule by default. It asks nothing about crop, target EC or source water, and it shows no predicted EC or ppm. Lettuce and a heavy-feeding fruiting plant get the same plan.

• For: Advanced Nutrients users who want a schedule rather than a single mix.

Rootless nutrient calculator

Our own nutrient calculator is an educational grams estimate, and its page says so. It assumes 1.2 mS/cm per gram per liter and splits the total across Grow, Micro and Bloom at fixed ratios: 50/30/20 in veg, 20/30/50 in flower. For 20 L at a target EC of 1.0 in veg, it gave Grow 8.3 g, Micro 5.0 g, Bloom 3.3 g (16.7 g in total).

• Strength: it is fast and brand-neutral, and it shows the arithmetic behind a target EC.
• Limitation: it does not ask for source-water EC, a product or a crop. If you type the full target of 1.0 into water that already reads 0.4, the reservoir will land nearer 1.4. Enter the difference, 0.6, instead, and follow your manufacturer's label for the real dose.
• For: learning how EC targets translate into grams, or a sanity check before you reach for the meter.

Brand calculators vs salt calculators

The outputs in the table are not interchangeable.

• A brand calculator answers "how many millilitres of our bottles?" The bottle's analysis is fixed by the manufacturer.
• A salt calculator like HydroBuddy answers "how many grams of potassium nitrate, calcium nitrate and magnesium sulfate for these element targets?"

The "ppm" a salt calculator talks about is the concentration of one element. It is not the ppm on a TDS meter, which is an estimate of total dissolved salts derived from EC with a 500 or 700 factor. HydroBuddy's author makes the same warning. If you need to move between EC and a meter's ppm, use the EC to PPM converter.

The number every calculator needs: your source water

None of the three web calculators asked for it, so you have to do this step yourself.

1. Measure the EC of your source water before adding anything.
2. Subtract it from the target.

With tap water at 0.4 and a lettuce target of 1.0, you are adding 0.6 mS/cm of nutrient, not 1.0. Skip the subtraction and a beginner reservoir runs 40% hot. That is enough to push lettuce above its 0.8–1.2 range.

Which calculator should you use?

• First grow, using a 3-part bottle set: use that brand's own calculator or chart, at its lightest schedule, and subtract your source water.
• Switching to dry salts to cut cost: HydroBuddy. Read mixing your own nutrients first for the cost comparison and the mixing order.
• You only want to know roughly how much to add for a target EC: the Rootless estimator, entering the EC above your source water.
• Commercial NFT or drip with an injector: a salt calculator plus stock solutions; brand charts rarely cover injector ratios.

After the calculator: verify

A calculator gives you a starting mix, not a result.

1. Add nutrients one at a time and stir between each.
2. Measure EC and correct towards target.
3. Adjust pH last. Our pH adjustment calculator estimates how much pH Down to add.

If EC drifts during the week, EC management explains what the direction of drift tells you about uptake. Keep the parameter reference open for other crops' targets. [UCD-LET-01]

Raw data

The inputs and outputs below are exactly what each tool returned on 2026-10-26. No recipe was mixed or measured.

FloraFlex's calculator address now redirects to a product page with a published schedule and no calculator, so it is not in the table. We could not find working official calculators for Green House Feeding or Jack's Nutrients on the test date.