Fertilizer Solution Mix Calculator

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Target profile:

Use a profile as a starting point, then confirm the targets against your crop plan and water analysis.

Finished reservoir volume:

Current equivalent: {{ reservoirEquivalent }}.

Target nitrogen (N):

For dilute working solutions, 1 ppm is treated as 1 mg/L.

ppm N

Target phosphorus (P):

Product P2O5 percentages are converted to elemental P inside the model.

ppm P

Target potassium (K):

Product K2O percentages are converted to elemental K inside the model.

ppm K

Blend objective:

Balanced is the normal starting point; nutrient-first modes only change how imperfect fits are ranked.

Fit tolerance:

{{ formatNumber(target_tolerance_percent, 1) }}%

Use the acceptance band defined by your recipe process; 5% is only a screening default.

Exact%

Fertilizer products:

Enable up to eight products. Enter the grade exactly as N-P2O5-K2O on the label.

Product preset:

Product name:

Nitrogen:

% N

Phosphate:

% P2O5

Potash:

% K2O

Injector ratio:

Use the setting from the calibrated injector or dosing system.

Stock tank size:

This planning value does not change the recipe for one finished reservoir.

Advisory stock load:

Use a product- and temperature-specific limit when known; 250 g/L is only a conservative review flag.

g/L

Fertilizer	Grade	Amount	N	P	K	Stock	Copy
{{ row.name }}	{{ row.grade }}	{{ row.amount }}	{{ row.n }}	{{ row.p }}	{{ row.k }}	{{ row.stock }}

A nutrient recipe describes what must be present in the finished irrigation water, while a fertilizer label describes the material available to supply it. Connecting the two requires more than matching three numbers. Nitrogen is normally stated as elemental N, but the phosphorus and potassium positions in an N-P-K grade are stated as P₂O₅ and K₂O, so those label percentages must be converted before they can be compared with elemental ppm targets.

For dilute working solutions, 1 ppm is treated as 1 milligram per liter. A target of 150 ppm N in 100 L therefore requires 15 g of elemental nitrogen. Doubling the reservoir volume doubles the nutrient mass and fertilizer weight, but it does not change the target concentration.

Finished solution: The water delivered to the crop, expressed here with elemental N, P, and K targets in ppm.
Fertilizer grade: The label percentages for N-P₂O₅-K₂O, not three elemental percentages.
Blend fit: The difference between the requested and achievable nutrient concentrations using non-negative amounts of the selected products.
Stock solution: A concentrate diluted by an injector into the finished irrigation stream.

Several fertilizers can supply more than one nutrient, so an exact match is not always possible. A product chosen to meet phosphorus may also add potassium or nitrogen. The useful result is therefore a mass-balanced recipe plus an honest statement of any remaining gap. Solubility, source-water nutrients, pH, electrical conductivity, crop stage, and chemical compatibility remain separate checks.

How to Use This Tool:

Start with the finished-water recipe and the grades printed on the products you will actually use.

Choose a Target profile or enter elemental nitrogen, phosphorus, and potassium targets. Confirm those ppm values against the crop plan and water analysis before treating them as a recipe.
Enter the Finished reservoir volume and unit. Changing units preserves the physical volume; changing the amount scales every fertilizer weight.
Enable the available products and enter each grade exactly as N-P₂O₅-K₂O. At least one enabled product must supply every nutrient with a positive target.
Use Balanced fit unless one nutrient must receive priority when no exact blend exists, then set the acceptance tolerance used by your own recipe process.
Enter the calibrated Injector ratio, stock-tank volume, and advisory load. Review the nutrient deltas and stock-density warning before weighing or mixing anything.

Interpreting Results:

Exact means every positive nutrient target is within 0.1 ppm. Within tolerance means the largest relative nutrient gap is no greater than the selected tolerance. Closest fit means the available grades cannot meet that band; inspect each nutrient delta instead of treating the recipe as acceptable.

The stock-density status compares calculated grams per liter with the advisory value you entered. It is not a solubility or compatibility guarantee. Verify product labels, manufacturer solubility limits, source-water contribution, and whether calcium products need separation from concentrated phosphate or sulfate products.

Technical Details:

The calculation first converts each target concentration into elemental nutrient mass. It then converts every enabled product grade to elemental mass fractions and searches for non-negative product weights that best reproduce the active targets.

Formula Core:

For nutrient i, the target mass and achieved concentration are:

\begin{array}{rcl} T_{i} & = & \frac{c_{i} V}{1000} \\ a_{i} & = & \frac{1000 \sum g_{j} f_{j i}}{V} \\ e_{i} & = & \frac{| a_{i} - c_{i} |}{c_{i}} \times 100 \end{array}

c_i is the target in ppm, V is finished volume in liters, T_i is elemental target mass in grams, g_j is grams of product j, f_ji is its elemental nutrient fraction, a_i is achieved ppm, and e_i is the absolute relative gap in percent.

Fertilizer label conversion to elemental nutrient fractions
Label entry	Elemental fraction used	Conversion
N	N	label % ÷ 100
P₂O₅	P	label % × 0.4364 ÷ 100
K₂O	K	label % × 0.8301 ÷ 100

The fit minimizes the weighted sum of squared relative gaps. Balanced fit uses equal N, P, and K weights; a nutrient-first objective gives the selected nutrient three times the weight. Candidate subsets contain at most three enabled products, negative weights are rejected, and ties favor the smaller maximum gap, fewer used products, then lower total mass.

Stock Concentration Rules:

\begin{array}{rcl} D & = & \frac{G R}{V} \\ G_{s} & = & D V_{s} \\ V_{c} & = & V_{s} R \end{array}

G is fertilizer mass for one finished reservoir, R is the injector ratio, D is stock density in g/L, V_s is stock-tank volume, G_s is fertilizer mass for that tank, and V_c is the finished-water volume it covers. Density at or below the advisory limit is inside the entered load; up to 125% of the limit is marked dense, and anything higher is marked very dense.

Accuracy and Safety Notes:

Targets are elemental N, P, and K only. Secondary nutrients, micronutrients, alkalinity, pH, and electrical conductivity are outside the calculation.
The product-name grouping is a mixing reminder, not a chemical compatibility test. Follow each manufacturer's order-of-addition and stock-tank guidance.
The advisory stock load is user supplied. Check actual solubility at the water temperature and concentration in use.
Measure the final solution and adjust for nutrients already present in source water before feeding a crop.

Worked Example:

For 100 L at 150 ppm N, 50 ppm P, and 200 ppm K, the default calcium nitrate, monopotassium phosphate, and potassium nitrate grades produce an exact fit at about 66.50 g, 22.03 g, and 36.09 g. Total product mass is about 124.63 g. With a 100:1 injector, stock density is about 124.63 g/L; a 20 L stock tank therefore needs about 2.493 kg and covers 2,000 L of finished solution.

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.