Short answer: divide the label’s per-gallon rate by four for a quart jar and by eight for a pint jar. For accuracy, it is easier to mix a full gallon and fill several jars from it.
Jar sizes as fractions of a gallon
| Jar | Volume | Fraction of a US gallon |
|---|---|---|
| Half gallon | about 1.9 L | 1/2 |
| Quart | about 0.95 L | 1/4 |
| Pint | about 0.47 L | 1/8 |
One US gallon is 3.785 liters. Mason jars are usually filled a little below the brim, so the actual solution volume is slightly less than the jar’s rated size.
A worked example
Suppose a label says 2 teaspoons per gallon.
- Quart jar: 2 ÷ 4 = 1/2 teaspoon
- Pint jar: 2 ÷ 8 = 1/4 teaspoon
For a liquid at 10 mL per gallon, a quart jar needs 2.5 mL and a pint jar 1.25 mL. A 3 mL or 5 mL syringe from a pharmacy measures these amounts far better than kitchen spoons.
Useful conversions
- 1 teaspoon ≈ 4.9 mL
- 1 tablespoon = 3 teaspoons ≈ 14.8 mL
- 1 liter ≈ 0.26 US gallons
Why mixing a gallon is better
Tiny doses are easy to get wrong. A few drops too many in a pint jar is a large error in percentage terms. Mixing a full gallon at the label rate, checking its EC and pH, and then filling jars from it gives every jar the same, measured solution. Leftover solution can fill the next jar or be used within a few days.
Two-part nutrients in jars
Measure and add each part separately, stirring between them, even for a single jar. Never combine the two parts in one syringe.
Related guide: how to mix Kratky nutrient solution.
