Fertilizer Solution Mix Calculator

Measurement system:

Metric uses L/m3; imperial uses gal/qt. Current cross-check: {{ reservoirSecondaryDisplay }}.

Target profile:

Start with Standard, Mild, High-K, or Heavy, then edit the ppm fields below for your recipe.

Blend objective:

Balanced treats N, P, and K evenly; nutrient-first options protect that ppm target.

Reservoir volume:

Enter the tank size to mix now; cross-check: {{ reservoirSecondaryDisplay }}.

Target nitrogen (N):

Use elemental N ppm (mg/L), such as 150 for a standard feed.

ppm

Target phosphorus (P):

Enter ppm P (mg/L), not P2O5; use 0 if phosphorus is not part of this mix.

ppm

Target potassium (K):

Enter ppm K (mg/L), such as 200; use 0 if potassium should not constrain the blend.

ppm

Target tolerance:

Slide 0-25%; 5% is a practical starting band for recipe screening.

{{ target_tolerance_percent }}%

Fertilizers:

Add soluble grades from the label; open each row to edit preset, name, and N-P2O5-K2O analysis.

Preset:

Choose a listed grade or Custom; always verify the bag label before mixing.

Fertilizer name:

Use the exact product or bag label, up to 80 characters.

Nitrogen (N):

Use the first N-P-K number, for example 15.5 for calcium nitrate 15.5-0-0.

Phosphate (P2O5):

Use the middle grade number, for example 52 for MKP 0-52-34.

Potash (K2O):

Use the final grade number, for example 46 for potassium nitrate 13-0-46.

Injector ratio:

Enter the dilution denominator only, such as 100 for a 1:100 injector.

1 :

Stock tank size:

Enter the stock container volume; units follow the measurement system selector.

Advisory stock-load guide:

Set a review limit in g/L, for example 250 for a conservative stock-density screen.

g/L

Fertilizer	Amount	Rate	Suggested stock group	N (ppm)	P (ppm)	K (ppm)	Copy
{{ row.name }}	{{ row.amountDisplay }}	{{ row.rateDisplay }}	{{ row.stockGroupDisplay }}	{{ row.n_ppm.toFixed(1) }}	{{ row.p_ppm.toFixed(1) }}	{{ row.k_ppm.toFixed(1) }}
No fertilizers in the recipe yet Enable at least one fertilizer with a usable N-P-K analysis to build the recipe sheet.

Nutrient	Target (ppm)	Achieved (ppm)	Difference	% of target	Status
{{ nutrient.label }}	{{ nutrient.targetDisplay }}	{{ nutrient.achievedDisplay }}	{{ nutrient.deltaDisplay }}	{{ nutrient.percentDisplay }}	{{ nutrient.status }}
No nutrient fit data available Enter a reservoir volume, target ppm values, and fertilizer analyses to calculate fit rows.
{{ item.title }}	Fit guidance	—	—	—	{{ item.title }}
Fit guidance	Pending	—	—	—	Fit notes will appear here when the recipe is calculated.

Fertilizer	Suggested stock group	Stock density	g for stock tank	Stock feed
{{ row.name }}	{{ row.stockGroupDisplay }}	{{ row.gramsPerStockLiterDisplay }}	{{ row.gramsForTankDisplay }}	{{ row.feedMlPerLiterDisplay }}
No stock readiness plan available A stock plan appears once the recipe has at least one fertilizer row and a valid injector setup.
{{ group.label }}	Suggested stock group total	{{ group.concentrationDisplay }}	{{ group.tankMassDisplay }}	{{ group.detail \|\| '—' }}
Concentrate compatibility	Reminder {{ index + 1 }}	—	—	{{ note }}
Concentrate compatibility	Reminder	—	—	Stock separation reminders will appear here when the recipe uses grades that deserve extra attention.

Section	Item	Detail
Guidance note	{{ item.title }}	{{ item.text }}
Guidance note	Pending	Recipe-specific guidance will appear here after calculation.
Mixing checklist	Step {{ idx + 1 }}	{{ item }}
Mixing checklist	Pending	Checklist items will appear here when the recipe is ready.

Enter reservoir size, targets, and fertilizer grades to build a recipe sheet and stock-readiness plan.

Embed:

Customize

Include current inputs

Size

Advanced

Width

Height

Aspect ratio

Max height

Collapsible embed

Allow fullscreen

Referrer policy

Sandbox tokens

Fertilizer solution mixing starts with a finished-water target, not with the numbers printed on a bag. A crop recipe may call for 150 ppm nitrogen, 50 ppm phosphorus, and 200 ppm potassium in the reservoir, while the available products are sold as fertilizer grades such as 15.5-0-0, 0-52-34, or 13-0-46. The mixing job is to translate those labels into elemental nutrient mass and then weigh a practical blend.

Parts per million is used because it describes concentration in the final feed water. For dilute nutrient solutions, 1 ppm is treated as 1 milligram per liter, so a 100 L reservoir at 150 ppm nitrogen needs 15 g of elemental nitrogen. If the reservoir volume doubles, the grams double. The ppm target itself does not change because the concentration in each liter stays the same.

Elemental target: The intended amount of N, P, or K in the final feed solution, expressed as ppm or mg/L.
Fertilizer grade: The label basis for a fertilizer product. Nitrogen is listed as elemental N, while phosphorus and potassium are commonly listed as P₂O₅ and K₂O.
Blend fit: How closely the weighed products can meet all active nutrient targets without using a negative amount of any product.
Stock solution: A concentrated mix that an injector dilutes into the final irrigation water, often around 1:100 in fertigation systems.

The label basis is where many recipes go wrong. A 0-52-34 monopotassium phosphate label does not mean the material is 52% elemental phosphorus and 34% elemental potassium. The phosphate and potash values include oxygen mass, so they must be converted to smaller elemental P and K fractions before the ppm target can be checked.

Soluble fertilizer products often overlap. Calcium nitrate supplies nitrogen, potassium nitrate supplies nitrogen and potassium, and monopotassium phosphate supplies phosphorus and potassium. Increasing one product can correct one nutrient while moving another nutrient away from target. A practical recipe is the blend that gets close to the requested elemental targets without asking for impossible negative grams.

The N-P-K fit is still not a complete nutrient-management decision. Water-source nutrients, alkalinity, electrical conductivity, pH, secondary nutrients, micronutrients, crop stage, solubility, and concentrate compatibility all affect whether a mix should be used. Calcium-bearing salts and phosphate or sulfate salts need special attention when they are mixed as strong stock solutions rather than dissolved directly into the final reservoir.

How to Use This Tool:

Work backward from the final feed solution. That keeps the recipe tied to the reservoir you intend to mix instead of to a fertilizer label ratio alone.

Choose Measurement system, then enter Reservoir volume. The cross-check line should show the equivalent volume in the other unit family.
Pick a Target profile for a starting point, or use Custom and enter Target nitrogen (N), Target phosphorus (P), and Target potassium (K) as elemental ppm targets.
Review each fertilizer row. Use a preset when it matches the product label, or choose Custom and type the product name with its N, P₂O₅, and K₂O percentages.
Use the row switch to keep only real candidate products active. If the page reports that no enabled fertilizer supplies a requested nutrient, enable or add a product that contains that element before reading the recipe.
Choose Blend objective when the active products cannot hit all targets equally. Balanced fit weights N, P, and K evenly, while a nutrient-first objective gives one nutrient three times the weight of the others.
Set Target tolerance before judging Fit Check. A wider tolerance can mark a nutrient as On target, but it does not change the achieved ppm.
Open Advanced when you need concentrate planning. Injector ratio, Stock tank size, and Advisory stock-load guide shape Stock Readiness, not the finished-solution N-P-K math.
Read Recipe Sheet, Fit Check, N-P-K Fit Chart, Stock Readiness, and Mixing Notes together before weighing materials.

Interpreting Results:

Recipe Sheet is the weighing list. It shows each enabled fertilizer, amount to add, working-solution rate, suggested stock group, and N, P, and K ppm contribution. A row at zero amount means the closest non-negative solve did not need that enabled product for the current targets.

Fit Check compares target ppm with achieved ppm for each nutrient. On target means the nutrient is inside the selected tolerance band. Above target and Below target identify the nutrient driving the miss, and the percent-of-target value shows whether the gap is small enough to accept or large enough to change products.

The summary label is stricter than a single nutrient badge. Exact fit means every active target lands within 0.1 ppm. Within tolerance means the recipe is not exact, but every active relative gap is inside the tolerance you selected. Closest fit means a non-negative recipe was found, but at least one active nutrient is outside tolerance.

Stock Readiness is a concentrate warning, not proof that the N-P-K math is wrong. Inside advisory load is at or below the chosen stock-load guide. Dense concentrate is above the guide and up to 1.25 times the guide. Very dense concentrate is beyond that 1.25 multiplier and deserves a different injector ratio, a larger stock tank, a split stock plan, or product-specific solubility review.

Do not treat a clean N-P-K fit as a complete crop recommendation. Use the final recipe alongside label limits, water testing, EC and pH readings, secondary nutrients, micronutrients, and a small-batch dissolve test when the concentrate looks dense or an A/B split is suggested.

Technical Details:

A fertilizer solution recipe is a mass-balance calculation. Ppm targets are converted into grams of elemental nutrient using the finished reservoir volume, then each fertilizer is represented by the elemental fraction it can supply per gram. The final check compares achieved ppm against target ppm after all product contributions are summed.

Fertilizer labels and hydroponic targets often use different chemical bases. Nitrogen percentages are already elemental. Phosphorus and potassium label values are oxide-equivalent values, so P₂O₅ is multiplied by 0.4364 and K₂O is multiplied by 0.8301 before the product can be compared with elemental P and K targets.

Formula Core:

\begin{array}{lcl} m_{E} & = & \frac{c_{E} \times V}{1000} \\ f_{j, P} & = & \frac{p_{j, 2 O 5} \times 0.4364}{100} \\ f_{j, K} & = & \frac{k_{j, 2 O} \times 0.8301}{100} \\ c_{E, achieved} & = & \frac{1000 \times \sum_{j}^{n} x_{j} f_{j, E}}{V} \end{array}

Fertilizer solution formula symbols and units
Symbol	Meaning	Unit or basis
`V`	Finished reservoir volume after unit conversion	L
`cE`	Target concentration for N, P, or K	ppm, treated as mg/L
`mE`	Elemental mass required in the finished reservoir	g
`xj`	Mass of fertilizer product j in the recipe	g
`fj,E`	Elemental fraction of nutrient E supplied by product j	g nutrient per g fertilizer
`cE, achieved`	Resulting concentration after all fertilizer contributions are summed	ppm

The blend solve checks non-negative combinations of active fertilizer rows, using up to three products at a time because there are three N-P-K constraints. Candidate recipes are ranked by exact fit, tolerance fit, weighted nutrient miss, largest relative gap, number of products used, and total mass. That ranking avoids recipes that only look neat because they would require a negative amount of one fertilizer.

Blend objective weights and result status boundaries
Rule area	Boundary or weighting	Practical meaning
Balanced fit	N, P, and K each use weight 1.	The overall relative miss is minimized evenly across active targets.
Nutrient-first fit	The selected nutrient uses weight 3; the other two use weight 1.	The solve protects one nutrient more strongly when all targets cannot be met together.
Exact fit	Every active target has an absolute gap no greater than 0.1 ppm.	The summary can call the recipe exact for display purposes.
Within tolerance	Every active relative gap is inside the selected tolerance band.	The recipe may be acceptable for screening even when it is not exact.
Closest fit	At least one active relative gap is outside tolerance.	The active products cannot satisfy every target within the selected band.

Stock concentration is calculated after the working recipe is solved. At a 1:100 injector ratio, a 100 L reservoir needs 1 L of stock to deliver one reservoir fill. If the recipe weighs 124.6 g total, the combined stock load is 124.6 g/L. Changing the injector ratio changes the concentrate load and coverage, but it does not change the grams required for the finished reservoir.

Fertilizer solution validation and stock boundaries
Input or output	Boundary	Effect
Nutrient targets	At least one of N, P, or K must be above zero.	Defines which nutrient constraints are solved.
Fertilizer analysis	Each N, P₂O₅, and K₂O percent must be from 0 to 100.	Controls the elemental fractions used in the mass balance.
Target tolerance	Must be from 0% to 50%.	Sets the relative band for On target and Within tolerance status.
Injector ratio	Must be from 1 to 5000.	Controls stock liters needed and concentrate load.
Advisory stock load	Must be greater than 0 and no more than 5000 g/L.	Defines the line between inside advisory load, dense concentrate, and very dense concentrate.

Suggested stock groups are advisory. Preset materials and name cues classify calcium-bearing products as Tank A, phosphate or sulfate products as Tank B, and simpler products as single or either. Actual compatibility still depends on product chemistry, water quality, concentration, temperature, mixing order, and label instructions.

Accuracy and Privacy Notes:

The calculation covers elemental N-P-K fitting, recipe weights, target-gap charts, and advisory stock-density checks. It does not verify every secondary nutrient, micronutrient, chloride or sodium contribution, product purity, hydration state, water-source nutrient contribution, pH shift, EC limit, crop-specific safety range, or exact solubility limit.

Use actual label grades and a scale with enough resolution, especially when a small batch asks for less than 1 g of any product.
Check dense concentrates and suggested A/B splits against product labels and solubility references before making a full stock tank.
The calculation runs in the browser after the page loads. If you share a URL that contains recipe settings or product names, treat that URL as part of the recipe record.

Worked Examples:

Standard 100 L reservoir

With metric units, a 100 L reservoir, and the standard 150 ppm N, 50 ppm P, and 200 ppm K target, the default fertilizer set lands on an exact displayed fit. Recipe Sheet gives about 66.5 g calcium nitrate 15.5-0-0, 22.0 g monopotassium phosphate 0-52-34, and 36.1 g potassium nitrate 13-0-46. Fit Check shows 150.0 ppm N, 50.0 ppm P, and 200.0 ppm K as On target.

Why monopotassium phosphate is sized first

For that 100 L example, the phosphorus target is 5 g elemental P. Monopotassium phosphate 0-52-34 has an elemental P fraction of 0.52 x 0.4364 = 0.226928, so the phosphorus target alone requires about 5 / 0.226928 = 22.0 g of product. Its potassium contribution is counted before potassium nitrate is sized.

Same feed, stronger concentrate

Keeping the same 100 L recipe but changing Injector ratio from 1:100 to 1:500 does not change the fertilizer weights for the finished solution. It raises the combined stock load from about 124.6 g/L to about 623.1 g/L, so Stock Readiness can move to Very dense concentrate while Fit Check still shows an exact nutrient fit.

Missing phosphorus source

If phosphorus remains above zero but every enabled fertilizer row has Phosphate (P2O5) set to zero, the page reports that no enabled fertilizer supplies phosphorus. Enable a phosphorus source such as monopotassium phosphate or monoammonium phosphate, or set the phosphorus target to zero if the recipe intentionally excludes P.

FAQ:

Should phosphorus and potassium targets be entered as P and K?

Yes. The target fields use elemental phosphorus and elemental potassium in ppm. Fertilizer row labels use P₂O₅ and K₂O percentages because many products report fertilizer grade on that basis.

Why did my target profile switch to Custom?

Editing the N, P, or K ppm fields away from a preset changes Target profile to Custom. The calculation still uses the visible ppm values.

Why can Fit Check say On target when the summary is not Exact fit?

On target follows the selected Target tolerance. Exact fit is stricter and requires every active nutrient to land within 0.1 ppm of its target.

What should I do with a Closest fit result?

Check the largest gap in Fit Check, then change the active fertilizer set, use a nutrient-first Blend objective, or adjust the target values. Raising tolerance only changes the acceptance band; it does not change the achieved ppm.

Do suggested stock groups guarantee compatibility?

No. The stock group hint is based on the entered grade and common calcium, phosphate, and sulfate separation patterns. Actual compatibility still depends on product chemistry, water quality, concentration, and mixing order.

Glossary:

ppm: Parts per million. For dilute fertilizer solutions, it is treated as milligrams of nutrient per liter of finished solution.
Elemental nutrient: The actual N, P, or K mass used for a target calculation, not the oxide-equivalent label basis.
P₂O₅: Phosphate label basis used for fertilizer grade; it is converted to elemental phosphorus before solving.
K₂O: Potash label basis used for fertilizer grade; it is converted to elemental potassium before solving.
Injector ratio: The dilution relationship between stock solution and final feed, such as 1:100.
Non-negative blend: A recipe where every fertilizer amount is zero or greater, so the math can be weighed in the real world.

References:

Hydroponics Systems: Calculating Nutrient Solution Concentrations Using the Two Basic Equations, Penn State Extension, updated January 12, 2026.
Hydroponics Systems: Using the Two Basic Equations to Calculate a Nutrient Solution Recipe, Penn State Extension, updated January 5, 2026.
Delaware Gardener's Guide to Lawn and Landscape Fertilizers, University of Delaware Cooperative Extension.
Understanding Your Fertilizer Types and Composition, Mississippi State University Extension, 2020.
Why should I use stock tanks?, Priva Help Center, November 18, 2025.

Fertilizer Solution Mix Calculator

{{ fitSummary.headline || 'Recipe Sheet Ready' }}

Current result

Fertilizers:

How to Use This Tool:

Interpreting Results:

Technical Details:

Formula Core:

Accuracy and Privacy Notes:

Worked Examples:

Standard 100 L reservoir

Why monopotassium phosphate is sized first

Same feed, stronger concentrate

Missing phosphorus source

FAQ:

Glossary:

References:

Fertilizer Solution Mix Calculator

{{ fitSummary.headline || 'Recipe Sheet Ready' }}

Current result

Fertilizers:

Introduction

How to Use This Tool:

Interpreting Results:

Technical Details:

Formula Core:

Accuracy and Privacy Notes:

Worked Examples:

Standard 100 L reservoir

Why monopotassium phosphate is sized first

Same feed, stronger concentrate

Missing phosphorus source

FAQ:

Glossary:

References: