Kombucha Batch Calculator
Calculate tea, sugar, and starter liquid amounts for any kombucha batch size.
Includes first and second fermentation ratios.
How kombucha ratios work:
Kombucha is fermented sweet tea. A SCOBY (Symbiotic Culture of Bacteria and Yeast) plus acidic starter liquid from a previous batch convert the sugar into organic acids, carbonation, and trace alcohol. The ratios must stay within safe ranges to prevent mold and off-flavors.
Standard first fermentation (F1) ratios:
| Ingredient | Amount per gallon | Purpose |
|---|---|---|
| Water | ~14 cups | Base liquid |
| Tea | 4–6 bags or 2–3 tbsp loose | Provides nitrogen and tannins for the SCOBY |
| Sugar | 1 cup (200g) | Food for the SCOBY — most is consumed |
| Starter liquid | 1–2 cups | Lowers pH to prevent mold |
| SCOBY | 1 per vessel | The living culture |
The golden ratios:
- Sugar: 1 cup per gallon (about 50g per liter)
- Starter liquid: 10–15% of total batch volume
- Tea: 4–6 tea bags per gallon (black, green, or a blend)
Worked example — 1 gallon batch:
- Boil 4 cups water, steep 5 tea bags for 10 minutes
- Dissolve 1 cup (200g) sugar in the hot tea
- Add cold water to fill to 14 cups
- Let cool to below 85°F (30°C)
- Add 2 cups starter liquid + SCOBY
- Cover with cloth, ferment 7–14 days at 72–82°F
Second fermentation (F2) — carbonation:
After F1, bottle the kombucha with added flavor:
- Fruit juice or puree: 10–20% of bottle volume
- Ginger, herbs: 1–2 tbsp per 16 oz bottle
- Seal tightly and leave at room temp for 2–4 days
- Burp bottles daily: pressure can cause glass to explode
- Refrigerate to stop fermentation and hold carbonation
Sugar consumption: The SCOBY consumes 70–90% of the sugar during F1. A finished kombucha typically has 2–5g sugar per 8 oz serving — far less than the 25g+ you started with.
pH safety: Finished kombucha should be pH 2.5–3.5. If pH stays above 4.0 after 7 days, discard the batch — the acid level is too low to prevent harmful bacteria growth.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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