Stock Solution to Target ppm
One millilitre of 20% stock holds 200 mg of solute. Ten litres at 800 ppm needs 8,000 mg, so 40 mL of stock. Fertiliser, sanitiser and nutrient mixes all work this way.
Your numbers
Stock needed
40mL
Dilution factor
250×
Per litre
4mL
Formula
Stock needed = Batch size (L) × Target ppm ÷ (Stock strength × 10000) × 1000
Dry fertiliser is labelled by nutrient ratio (20-20-20), not a single percentage. Pull out the percentage of the nutrient you are targeting first.
What to enter
| Input | Default | Accepted range |
|---|---|---|
| Batch size (L)How much finished liquid you want, in litres. | 10 | 0 and up |
| Stock strength (%)The concentration printed on the undiluted stock. | 20 | 0.01 ~ 100 |
| Target ppmThe concentration you are aiming for, in parts per million. | 800 | 0 and up |
Step by step
Quick reference table
Results when only Batch size (L) changes and everything else stays put.
| Batch size (L) | Stock needed (mL) | Dilution factor (×) | Per litre (mL) |
|---|---|---|---|
| 5 | 20 | 250 | 4 |
| 7.5 | 30 | 250 | 4 |
| 10 | 40 | 250 | 4 |
| 15 | 60 | 250 | 4 |
| 20 | 80 | 250 | 4 |
What each result means
| Result | At default values |
|---|---|
| Stock needed (mL)How much stock to draw off to hit that concentration. | 40 |
| Dilution factor (×)How many times the concentrate was expanded — 1 part to how many. | 250 |
| Per litre (mL)Concentrate to add for every litre of water. | 4 |
Common mistakes
Dry fertiliser is labelled by nutrient ratio (20-20-20), not a single percentage. Pull out the percentage of the nutrient you are targeting first.
Glossary
- Batch size (L)
- How much finished liquid you want, in litres.
- Stock strength
- The concentration printed on the undiluted stock.
- Target ppm
- The concentration you are aiming for, in parts per million.
- Stock needed
- How much stock to draw off to hit that concentration.
- Dilution factor
- How many times the concentrate was expanded — 1 part to how many.
- Per litre
- Concentrate to add for every litre of water.
Frequently asked questions
Q. How is Stock Solution to Target ppm calculated?
Stock needed = Batch size (L) × Target ppm ÷ (Stock strength × 10000) × 1000 — One millilitre of 20% stock holds 200 mg of solute. Ten litres at 800 ppm needs 8,000 mg, so 40 mL of stock. Fertiliser, sanitiser and nutrient mixes all work this way.
Q. Can you walk through an example?
With Batch size (L) 10, Stock strength 20%, Target ppm 800, the answer is Stock needed 40mL.
Q. What do I need to enter?
Enter Batch size (L), Stock strength, Target ppm. The result recalculates as you type, and an empty box counts as zero.
Q. How much does the answer move if I change a number?
Changing only Batch size (L) moves the answer to Batch size (L) 5 → Stock needed (mL) 20 and Batch size (L) 20 → Stock needed (mL) 80. The table below lays out five steps.
Q. How are the numbers rounded?
Money is shown to the nearest whole unit, percentages to one decimal place and everything else to two. What you see is rounded; the calculation itself carries the unrounded value forward.
Q. Anything to watch out for?
Dry fertiliser is labelled by nutrient ratio (20-20-20), not a single percentage. Pull out the percentage of the nutrient you are targeting first.
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