Cal Mag Dose Calculator

Balance calcium and magnesium targets with clear dosing steps. Convert liters and gallons, then validate label strength. Export clean reports for repeatable feeding habits.

Calculator inputs

Enter your reservoir size, target ppm increases, and label strength.
Use clean measuring tools for accuracy
Used to convert ppm targets into mg required.
Conversions are automatic in the results.
Helpful when applying larger adjustments.
Calcium increase target in ppm (mg/L).
Magnesium increase target in ppm (mg/L).
Prevents unusually large single-step additions.
Product label method
Choose how your cal-mag label reports strength.
Elemental calcium percentage, not CaO.
Elemental magnesium percentage, not MgO.
Use label/SDS if available. Default 1.00.
Enter elemental calcium per mL.
Enter elemental magnesium per mL.
If your label lists mg/L per mL/L, multiply by 1.0 to get mg/mL.
If your product uses oxide forms, convert to elemental first: CaO → Ca × 0.714, MgO → Mg × 0.603.

Example data table

These examples assume a product labeled 3% Ca and 1% Mg with density 1.00 g/mL.
Water volume Target Ca increase Target Mg increase Estimated dose
10 L 30 ppm 10 ppm 100 mL
20 L 40 ppm 20 ppm 400 mL
5 gal 25 ppm 15 ppm ~284 mL
Your label strength may differ, so always calculate with your own numbers.

Formula used

1) Convert ppm target to required mass
In water, 1 ppm ≈ 1 mg/L.
Required mg = Target ppm × Volume (L)
2) Convert label strength to mg per mL
Using % w/w and density (g/mL):
mg/mL = (Percent ÷ 100) × Density × 1000
3) Dose calculation
Dose per element = Required mg ÷ (mg per mL). If you set both Ca and Mg targets, the calculator recommends the larger dose so neither target is missed.
Dose (mL) = max(DoseCa, DoseMg)

How to use this calculator

  1. Measure your water volume and select liters or gallons.
  2. Enter the ppm increases you want for calcium and magnesium.
  3. Choose how your product label reports strength.
  4. If using % values, keep density at 1.00 unless known.
  5. Press Calculate dose to view results above the form.
  6. Use the CSV or PDF buttons to save the result sheet.

Calcium and magnesium targets

Cal-mag dosing is most useful when irrigation water is soft, reverse-osmosis filtered, or consistently low in dissolved minerals. This calculator focuses on ppm increases, helping you plan controlled steps instead of guessing a “capful.” Typical garden programs aim for stable availability rather than frequent spikes.

For planning, many growers treat cal-mag as a ratio tool: if your program targets a Ca:Mg balance near 2:1 to 4:1, adjust the two ppm fields accordingly and let the fixed product ratio do the work. Use your recent water test as the baseline, then calculate only the difference you need to add.

What the dose number represents

The recommended total dose is the product volume (mL) needed to reach your selected calcium and/or magnesium increase in the chosen water volume. If both targets are entered, the calculator uses the larger of the two computed doses so one nutrient does not fall short. The result also shows the estimated ppm you will achieve.

Label strength inputs and reliability

Some labels show % calcium and % magnesium, while others list mg/mL or a derived “ppm per mL per liter” statement. The percent method uses density to convert mass percent into mg/mL. If density is unknown, 1.00 g/mL is a reasonable starting assumption, but verify via SDS or manufacturer data for tighter accuracy.

Practical limits and split scheduling

Large nutrient corrections can stress plants and shift pH. Use the optional dose cap to limit one-time additions, then split across multiple days using the scheduling field. For example, a 120 mL correction split over 3 days becomes 40 mL/day, improving stability. Always mix thoroughly and re-test after circulation time.

Data tracking and exports

Exported CSV and PDF outputs help you log reservoir adjustments, compare batches, and maintain consistency across beds or containers. Recording water volume, targets, and achieved ppm estimates supports repeatability and faster troubleshooting when growth slows or leaf symptoms appear. Pair exports with date, cultivar, and EC readings for better context.

FAQs

1) Does this work for soil, coco, and hydro?

Yes. It calculates nutrient addition to water. Apply the mixed solution in any system, then watch runoff or reservoir readings to confirm the change matches your goals.

2) What if my label lists CaO or MgO instead of Ca or Mg?

Convert oxides to elemental first. Use CaO × 0.714 for calcium and MgO × 0.603 for magnesium, then enter the converted percent values to avoid overestimating delivery.

3) Why does the calculator choose the larger of two doses?

Many cal-mag products deliver Ca and Mg in a fixed ratio. If you must satisfy both targets, the larger computed dose prevents one nutrient from being under-delivered at the selected volume.

4) My result looks huge. What should I do?

Confirm units, density, and whether your label is elemental or oxide-based. Then apply a dose cap and split dosing across days. Re-test after mixing before adding more.

5) Can I use this for ppm reductions?

No. This tool plans increases only. To reduce ppm, dilute with low-mineral water or replace part of the reservoir, then re-calculate the smaller increase needed afterward.

6) How accurate are the achieved ppm estimates?

They are as accurate as your label data and measuring tools. Real-world results vary with temperature, mixing, and test method. Use the estimate as a planning guide and verify with measurement.

Related Calculators

Greenhouse size calculatorGreenhouse floor area calculatorGreenhouse volume calculatorBench space calculatorGrowing area calculatorPlant density calculatorPot count calculatorTray count calculatorRack capacity calculatorLayout efficiency calculator

Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.