First Rays TDS Calculator

Calculator Inputs

Enter fertilizer label data, dose details, source water TDS, and target limits.

Fertilizer name

Calculation mode

Target mode ignores fixed dose for the main calculation.

Batch volume

L

Fixed dose amount

Dose unit

Target nitrogen

ppm

Nitrogen on label

%

Phosphate on label

% P2O5

Potash on label

% K2O

Calcium

%

Magnesium

%

Sulfur

%

Trace or other nutrients

%

Soluble fraction

%

Use 100 for fully soluble fertilizer.

Powder density estimate

g/tsp

Liquid density

g/mL

Source water TDS

ppm

Target final TDS

ppm

TDS factor

Typical meters use an approximate conversion factor.

Measured final TDS

ppm

Optional. Enter 0 to skip comparison.

Notes

Reset

Formula Used

Dose and Nutrient PPM

g/L from tsp/gal = teaspoons × grams per teaspoon ÷ 3.78541

P actual = P2O5 × 0.4364

K actual = K2O × 0.8301

Nutrient ppm = g/L × 1000 × nutrient percent ÷ 100

TDS, EC, and Dilution

Fertilizer TDS = g/L × 1000 × soluble fraction

Final TDS = source water TDS + fertilizer TDS

EC mS/cm = TDS ÷ conversion factor ÷ 1000

Water to add = volume × (current TDS − target TDS) ÷ (target TDS − source TDS)

How to Use This Calculator

Enter the fertilizer name and label analysis.
Choose fixed dose or target nitrogen mode.
Add source water TDS and target final TDS.
Enter powder density or liquid density when needed.
Press calculate and review the result section above the form.
Use the chart to compare nutrient and TDS shares.
Download the CSV file for spreadsheet records.
Download the PDF file for a printable report.

Example Data Table

Example Mix	Label	Dose	Source TDS	Target TDS	Use Case
Balanced grow feed	20-20-20	1 tsp/gal	60 ppm	450 ppm	General orchid feeding
Low strength feed	13-3-15	0.5 tsp/gal	35 ppm	300 ppm	Sensitive roots
Target nitrogen plan	MSU style 13-3-15	100 ppm N	25 ppm	500 ppm	Consistent feeding records
Flush check	0-0-0	0 tsp/gal	40 ppm	100 ppm	Compare water only

Why TDS Matters

Total dissolved solids help growers compare fertilizer mixes with one number. The reading does not show every nutrient separately. It still gives a useful strength check. A low reading may mean the mix is weak. A high reading may warn about salt stress. This calculator turns label values into practical estimates.

Better Feeding Decisions

First Rays style fertilizer math starts with the label. Nitrogen is listed as elemental nitrogen. Phosphorus and potassium use oxide forms. The tool converts P2O5 to actual phosphorus. It also converts K2O to actual potassium. Then it estimates ppm from dose, volume, and concentration. You can use a fixed dose. You can also choose a target nitrogen level. That helps when different products have different analysis numbers.

TDS, EC, and Water

A meter usually reads electrical conductivity. Many meters display TDS by applying a factor. This factor changes with the minerals in the water. The default factor in this page is adjustable. Source water is also included. That matters because fertilizer is not the only source of dissolved solids. Hard tap water can push the final reading much higher than expected.

Using the Results

Review the nitrogen ppm first. It is often the main feeding control. Next, check phosphorus and potassium. Then review the estimated fertilizer TDS and final solution TDS. If the target is exceeded, the page estimates clean water needed for dilution. The chart helps compare nutrient shares. The table can be saved for records. Use the CSV file for spreadsheets. Use the PDF button for quick reports.

Practical Notes

These results are estimates. Labels are rounded. Powders vary by scoop density. Liquids vary by specific gravity. TDS meters react differently to each ion. Temperature and calibration also change readings. For sensitive plants, start lower. Watch leaf tips, roots, and growth. Increase strength slowly when plants respond well. Keep notes for each season. A steady method is more useful than one perfect number. This tool gives a repeatable starting point for feeding, flushing, and comparing fertilizer choices.

Recheck meters monthly with calibration solution. Rinse probes after use. Store results with plant notes, water source, and weather changes for better comparisons later.

FAQs

1. What does this calculator estimate?

It estimates fertilizer dose, nutrient ppm, final TDS, EC, dilution needs, and batch product quantity. It uses label percentages, dose settings, source water TDS, and a chosen TDS factor.

2. Is TDS the same as nutrient strength?

No. TDS is a broad dissolved solids estimate. It does not identify each nutrient. Nitrogen ppm is often a clearer feeding strength guide for fertilizer planning.

3. Why are P2O5 and K2O converted?

Fertilizer labels usually list phosphorus as P2O5 and potassium as K2O. The calculator converts those oxide values into elemental phosphorus and potassium for ppm estimates.

4. What TDS factor should I use?

Many meters use a factor near 0.5, 0.64, or 0.7. Use your meter manual when possible. The default is only an adjustable estimate.

5. Why include source water TDS?

Source water already contains dissolved solids. Tap water can add calcium, magnesium, salts, or carbonates. Final TDS should include both water and fertilizer contributions.

6. Can I use liquid fertilizer?

Yes. Choose a milliliter dose unit and enter liquid density. The calculator converts volume into an estimated gram dose before nutrient and TDS calculations.

7. Why does measured TDS differ?

Meter calibration, temperature, ion type, label rounding, scoop density, and water chemistry can change readings. Use the comparison field to track the difference.

8. Is this safe for every plant?

No calculator can guarantee plant safety. Start with weaker mixes for sensitive plants. Watch roots and leaf tips. Adjust slowly based on growth and response.