Best Free Hydroponic Calculators and References 2026

Disclosure: SciHub101 is owned by the same team that builds Rootless Farm. We've listed it first because it fits the criteria below, but we've tried to judge every option, including our own, by the same standard. Weaknesses of every pick are listed.

Hydroponic growing replaces soil with a nutrient solution, so a few numbers decide whether your lettuce thrives or stalls: electrical conductivity (EC), pH, light, and reservoir volume. You can get those numbers right with free tools. This guide compares six free or mostly free options for home growers, and it ranks them on a narrow question: where can a beginner find calculators and crop-specific reference data in the same place, with the sources visible?

How we picked

We used four criteria for home and small-scale growers.

1. Free to use. Can you do the core calculations without paying or creating an account?
2. Shows its work. Does it give a formula, a source, or a clear statement of what it assumes?
3. Breadth for beginners. Does it cover nutrient mixing, EC, pH, light, and sizing?
4. Crop-specific reference. Does it tell you target values for particular plants?

We read each provider's own pages on October 4, 2026, and we report only what they state. We did not run side-by-side accuracy tests of the math, so none of these tools is "verified correct" by us. No one should treat a calculator as a replacement for measuring your own water.

Comparison at a glance

Option	Type	Cost (per its page)	Crop profiles	Best for
Rootless Farm	Web calculators and reference	Free tools; paid Grower and Pro plans	53 plants	Calculators plus crop data in one place
Cornell CEA home guide	PDF and Excel tool	Free	Leafy greens	A university-written starting point
Cornell CEA handbooks	PDF handbooks	Free	Lettuce and spinach	Deeper crop-specific production detail
Penn State calculator	Spreadsheet	Free to download	Designed for DWC lettuce	Topping up a recirculating solution
HydroBuddy (Science in Hydroponics)	Desktop-style calculator	Free, open source (per author)	Custom formulations	Turning a ppm recipe into salt weights
UF/IFAS HS405	Fact sheet	Free to read	Florida commercial crops	Understanding system types and economics

Rootless Farm is the broadest in one place; the university sources carry the most institutional authority.

1. Rootless Farm: calculators and crop profiles together

Best for: Beginners and hobbyists who want nutrient, light, and sizing calculators next to per-crop reference data.

Rootless Farm describes itself as a hydroponics field manual. Its homepage lists 53 plant profiles, including lettuce, basil, cherry tomato, strawberry, arugula, and bell pepper, with pH, EC, daily light integral (DLI, the total light a plant receives in a day), and growth-cycle data. It also lists 18 calculators and AI tools covering nutrient mixing, EC to ppm conversion, vapor pressure deficit (VPD, a measure of how thirsty the air is), DLI, pH adjustment, LED hanging height, reservoir volume, system sizing, and a germination calendar. It also describes results that carry formulas or citations, a troubleshooting ledger with 25 documented diagnoses, and AI diagnosis from leaf photos with confidence scoring.

The homepage says all calculators and reference pages are free without an account. Paid plans are listed as Grower at $2.99 per month, for a workspace that tracks several systems, and Pro at $29.99 per year, which adds sensor integration. The site also mentions an iOS app.

Limitations:

• The tools page marks four items as Pro: the Commercial Hydroponic ROI Estimator, AI Equipment Kit Builder, Hydroponic Crop Planner, and AI Nutrient Deficiency ID. "All calculators free" on the homepage and four Pro tools on the tools page do not fully agree, so check which tool you need.
• The site says every claim is sourced. We have not audited each one.
• A photo-based AI diagnosis gives an estimate with a confidence score, not a lab result. Confirm with a water test.
• We have not seen independent validation of its calculators.

2. Cornell CEA home hydroponics guide and Excel tool

Best for: A trustworthy, university-written first read.

Cornell's Controlled Environment Agriculture program offers "A Guide to Home Hydroponics for Leafy Greens" as a free PDF, plus an Excel tool with calculations that accompany the guide.

Limitations: It is a guide, not an interactive calculator suite, and it focuses on leafy greens. Expect to work in a spreadsheet.

3. Cornell CEA lettuce and spinach handbooks

Best for: Growers who want crop-specific production detail.

Cornell also posts the Hydroponic Lettuce Handbook and Hydroponic Spinach Handbook as free PDFs. All of Cornell's listed materials appear to be free.

Limitations: They cover two crops, and they read as production manuals, so you need patience. They do not calculate anything for you.

4. Penn State Extension fertilizer calculator

Best for: Growers who recirculate their solution and want to back-add single elements.

Penn State describes a free spreadsheet that helps hydroponic growers back-add single elements to a recirculating solution and save on fertilizer. It was designed in commercial deep water culture (DWC, roots floating in aerated solution) lettuce operations, and ranges can be adjusted for other crops.

Limitations: It needs a current water or nutrient solution test from an accredited lab. If you do not test, it cannot help. It is built for commercial lettuce, so home growers of other crops must adapt it.

5. HydroBuddy on Science in Hydroponics

Best for: Converting a target nutrient recipe into the weights of fertilizer salts.

The Science in Hydroponics author describes a calculator that translates a formulation in ppm into the weight of each salt, with options for stock solutions, water quality inputs, saved formulations, and pH and EC logging. The page includes a useful warning: the ppm in a recipe is not the same as the ppm shown on an EC meter. EC meters measure how well the solution conducts electricity, which works like a proxy for total dissolved salts, while recipe ppm counts specific nutrients.

The author describes HydroBuddy as free and open source, with features for 1:100 concentrated stock solutions, a "straight addition" mode for dosing directly into the reservoir, and a reverse calculation that works out ppm from salt weights you already use.

Limitations: The original feature post dates from August 2010, so check the author's blog for the current download and supported platforms. It also assumes you already understand recipes and salts, which can overwhelm a first-time grower.

6. UF/IFAS "Hydroponic Vegetable Production in Florida"

Best for: Understanding system types and the economics of greenhouse production.

This University of Florida extension publication, by Richard Tyson, Robert Hochmuth, and Daniel Cantliffe, covers Florida's hydroponic vegetable industry, marketing, growing systems including perlite, rockwool, NFT (nutrient film technique), and floating raft, fertilizer management, seasonal limits, and economics.

Limitations: It is a fact sheet for commercial greenhouse growers, not a home-gardening tool, and it contains no calculators.

A short history: why home hydroponics got easier

Growing in nutrient solution is not new, but the methods most home growers use today came out of university research aimed at making the process cheaper and simpler. Two threads matter for anyone choosing tools.

The first is the move away from pumps. Bernard Kratky, a horticulture professor at the University of Hawaii's College of Tropical Agriculture and Human Resources (CTAHR), began developing a non-circulating method in 1987. In a 2009 paper, "Three non-circulating hydroponic methods for growing lettuce," he described systems that need no electricity, pumps, or wicks. All of the nutrient solution goes in before planting. In the simplest version, lettuce is seeded in a tapered net pot of growing medium set into a darkened 4-liter plastic bottle, with only the lower 3 cm of the pot in the solution. As the plant drinks, the solution level drops and an air gap opens for the upper roots. CTAHR reports that the method was granted two U.S. patents and has been adopted by commercial growers, schools, and hobbyists.

The second thread is the shift in commercial systems. The UF/IFAS fact sheet notes that rockwool dominated Florida's greenhouse vegetable industry in the 1990s before growers moved toward perlite. It also records why many tomato growers abandoned recirculating systems: when solution is not recirculated, root infections stay localized instead of traveling through the whole system.

Both threads explain why the calculators in this list exist. A pumpless jar needs a correct starting mix because you rarely touch it again. A recirculating system needs ongoing correction because the solution changes as plants feed. Different tools fit those two jobs.

The numbers that matter, and what each tool does with them

Electrical conductivity (EC)

EC tells you how strongly the solution conducts electricity. More dissolved fertilizer salts mean higher conductivity, so EC works as a fast stand-in for "how strong is my mix." It does not tell you which nutrients are present, only the total.

Units cause much of the confusion. Research papers often use decisiemens per meter (dS/m). Many hobby meters show millisiemens per centimeter (mS/cm) or microsiemens per centimeter (µS/cm). The first two are the same number: 1.3 dS/m equals 1.3 mS/cm, which equals 1,300 µS/cm. If a guide and your meter disagree by a factor of 1,000, check the unit before you check the fertilizer.

What the research says about EC for lettuce

Purdue University's extension bulletin HO-309-W, by Alexander Miller, Petrus Langenhoven, and Krishna Nemali (March 2020), is one of the clearest public tests of how strong a lettuce solution should be. The team grew 24 lettuce varieties, including leaf, romaine, butterhead, and oakleaf types, at four target EC levels: 1.3, 2.0, 2.9, and 3.9 dS/m. They used two systems, nutrient film technique (NFT) and constant flood table (CFT), and harvested after four weeks.

Three findings are useful for home growers:

• Growth was higher at the two lower levels (1.3 and 2.0 dS/m) and lower at 2.9 and 3.9 dS/m.
• The authors attribute the drop to osmotic stress. At high salt concentration, roots struggle to take up water and nutrients.
• The optimum did not change with system or variety. The authors recommend 1.3 dS/m for lettuce in both NFT and CFT.

The bulletin also raises a point many beginners miss. More fertilizer than a slow-growing variety needs can raise nutrient levels in the leaf tissue, and the authors note that high nitrate levels in leaf tissue are not desirable for human health. Stronger is not automatically better.

pH

pH controls whether nutrients that are present in the solution are available to roots. Extension guidance generally targets a slightly acidic solution for leafy greens and advises checking pH after the EC is in range, because adding concentrated fertilizer shifts pH. Look up the target for your crop in a source you trust, such as the crop handbooks above or a crop profile, rather than using one number for everything.

Where each tool fits

Job	Tool on this list that addresses it
Convert meter units and readings	Rootless Farm's EC to ppm converter
Turn a ppm recipe into grams of salts	HydroBuddy
Back-add single elements from a lab test	Penn State spreadsheet
Find a target range for a specific crop	Rootless Farm crop profiles, Cornell handbooks
Plan light	Rootless Farm DLI and LED height tools
Choose a system type	UF/IFAS HS405, Cornell home guide

A worked example: your first lettuce reservoir

This example shows the order of operations, not a recipe. Use the label on your own fertilizer and the targets from a source you trust.

1. Measure your tap water first. Fill a clean container, read EC and pH, and write both down. Hard water already carries dissolved minerals, so it starts with a non-zero EC. HydroBuddy's description lists water quality inputs for this reason, and the Penn State calculator goes further by asking for an accredited lab test.
2. Work out reservoir volume. A rectangular tub that is 40 cm long, 30 cm wide, and filled 20 cm deep holds 40 × 30 × 20 = 24,000 cm³, or 24 liters. A reservoir volume calculator does the same arithmetic, and it is worth doing, because every dose scales with volume.
3. Pick a target. For lettuce, the Purdue result points to about 1.3 dS/m. Write the target in the unit your meter displays.
4. Mix in steps. Add part of the fertilizer dose, stir, wait, and measure. Repeat until you approach the target. Adding the whole calculated dose at once leaves no room for the difference between your water and the calculator's assumptions.
5. Adjust pH last. Once EC is in range, measure pH and adjust in small amounts.
6. Log it. Record the date, volume, EC, pH, and what you added. HydroBuddy and Rootless Farm both describe logging features, and a paper notebook works equally well.
7. Watch the trend, not one reading. In a recirculating system, Purdue's extension material describes adding stock solution to the recycled solution to hold EC at the target, along with periodic draining. A record of readings over days tells you which direction things are moving.

Common mistakes the tools will not catch for you

• Mixing up recipe ppm and meter ppm. The HydroBuddy author warns that ppm values in a recipe have "NOTHING to do with" the ppm your EC meter shows. A meter's ppm is a conversion from conductivity, and different meters use different conversion standards. Record EC instead of ppm whenever you can.
• Assuming more fertilizer means more growth. Purdue's lettuce trial found lower growth at the two higher concentrations.
• Trusting a meter that has not been calibrated. A calculator is only as good as the reading you enter. Follow your meter's calibration instructions.
• Treating a recirculating system as disease-proof. The UF/IFAS fact sheet records that growers moved away from recirculating tomato systems over concerns that root pathogens spread through shared solution.
• Copying a commercial number to a jar. Penn State's spreadsheet was designed in commercial deep water culture lettuce operations. Its ranges are adjustable, but its defaults reflect that setting.
• Using one target for every crop. A crop profile or handbook exists because lettuce, basil, and tomatoes are not the same plant.

Misconceptions worth clearing up

"Hydroponics needs pumps and electricity." The Kratky method needs neither, per CTAHR's own description. Pumps help larger and recirculating systems, but a jar on a windowsill can grow lettuce.

"An AI photo diagnosis replaces a water test." A photo shows symptoms. Several different causes, from pH problems to light stress, can produce similar-looking leaves. Rootless Farm presents its diagnosis with a confidence score, which is an honest way to signal uncertainty. Measure EC and pH before changing your mix.

"University material is only for farms." Cornell's home guide is written for home growers of leafy greens. The commercial focus applies to the handbooks, the Penn State spreadsheet, and the UF/IFAS fact sheet.

Privacy and data notes

Most of these tools ask for very little. Rootless Farm's homepage says every calculator and reference page is free with no account. Its paid tiers add a workspace for several systems and, on Pro, sensor data ingestion, which means your readings are stored by the service. The Cornell, Penn State, and UF/IFAS materials are documents and spreadsheets that run on your own computer once downloaded. HydroBuddy is described by its author as free and open source.

If you upload leaf photos to any AI diagnosis service, assume the image is processed off your device unless the service states otherwise, and read its privacy policy first. Rootless Farm links to editorial standards and an AI transparency page from its homepage.

Which one should you start with?

• Complete beginner: Read the Cornell home guide, then try a free calculator on Rootless Farm to see how the numbers move.
• Recirculating system with lab results: Use the Penn State spreadsheet.
• Want the cheapest possible start: Try a single Kratky jar of lettuce, as described in the CTAHR paper, and use a calculator only for the starting mix.
• You already know your recipe: Use HydroBuddy to get salt weights.
• Thinking about scaling up: Read the UF/IFAS fact sheet and the Cornell handbooks.

Hydroponics is also a sustainability topic, since it changes how a crop uses water and land. For background, see how soil works, photosynthesis, how the water cycle works, water scarcity, and AI in precision agriculture.

Frequently asked questions

Q: Do I need an app to grow hydroponically?
A: No. A notebook and a spreadsheet work. Calculators save time and cut arithmetic errors, but they do not replace measuring your own EC, pH, and water.

Q: Is ppm on a calculator the same as ppm on my EC meter?
A: No. The HydroBuddy author warns that recipe ppm values have nothing to do with the ppm an EC meter shows, because meters estimate total dissolved salts from conductivity.

Q: Are Rootless Farm's calculators really free?
A: Its homepage says calculators and reference pages are free without an account, and its tools page marks four tools as Pro. Check the tool you need on the site.

Q: Which source is most authoritative?
A: University programs such as Cornell CEA, Penn State Extension, and UF/IFAS carry institutional authority. We still suggest comparing at least two sources before changing a nutrient recipe.

Q: What EC should I use for hydroponic lettuce?
A: Purdue University's 2020 trial of 24 lettuce varieties found the best growth at 1.3 and 2.0 dS/m and recommends 1.3 dS/m for both NFT and constant flood systems. Growth was lower at 2.9 and 3.9 dS/m, which the authors attribute to osmotic stress.

Q: Can I grow hydroponically without a pump?
A: Yes. The Kratky method, developed by Bernard Kratky at the University of Hawaii, uses no electricity, pumps, or wicks. All the solution is added at the start, and the plant draws the level down as it grows.

Q: Are dS/m and mS/cm the same?
A: Yes, they are numerically equal, so 1.3 dS/m is 1.3 mS/cm, or 1,300 µS/cm. Check which unit your meter shows before comparing it with a guide.

Q: Should I adjust pH or EC first?
A: Get EC into range first, then check and adjust pH, because adding concentrated fertilizer changes pH.

The takeaway

Rootless Farm earns the top slot on a specific, stated measure: it puts crop profiles and a full set of calculators in one place that is largely free to use. University sources beat it on authority, and the spreadsheet tools beat it on narrow jobs. Use two sources, measure your own water, and let your plants, not a ranking, tell you what works.

Sources checked on October 4, 2026: rootlessfarm.com and its tools page, Cornell CEA, Penn State Extension, Science in Hydroponics, UF/IFAS HS405, Purdue Extension HO-309-W, and University of Hawaii CTAHR.

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Read next:

• How Photosynthesis Works
• How the Water Cycle Works
• AI Sustainable Agriculture: Precision Farming