Scale a kombucha recipe to any batch
Kombucha is sweet tea fermented by a culture of yeast and bacteria, often called a SCOBY. A reliable batch depends on proportions: enough sugar to feed the culture, enough tea for flavour and nutrients, and enough already-sour kombucha (starter liquid) to bring the acidity down quickly. This kombucha recipe calculator turns a batch size into grams of tea and sugar, millilitres of starter, hot water and cold water, and then works out the juice or sugar for a second ferment in the bottle.
Defaults follow common home ratios: about 8 g of tea and 60 g of sugar per litre with 10% starter liquid. You can change any of them. The page also warns when a value is outside the usual range. Everything runs in your browser and nothing is uploaded.
How to use the Kombucha Recipe Calculator
- Enter the batch size in litres, US gallons or US quarts.
- Check the tea, sugar and starter figures; change them if your recipe differs.
- Choose a second ferment of fruit juice or plain sugar, or none.
- Read the quantities, brew the sweet tea, cool it, add the starter and culture, and test the acidity before bottling.
Kombucha Recipe Calculator features
Any unit
Litres, US gallons or US quarts, converted to litres for the maths.
Hot and cold water
A quarter of the volume steeps the tea and dissolves the sugar; the rest cools it down.
Starter kept back
The starter liquid for the next batch is taken from this one before bottling.
Second ferment
Juice as ml per 100 ml of kombucha, or sugar as grams per litre.
Range warnings
Notes appear for very low starter or sugar outside the usual 50–70 g per litre.
The first and second ferment
In the first ferment the culture converts the sugar in the tea to acids, a little alcohol and a trace of carbon dioxide in an open vessel covered with cloth. It usually takes 7 to 14 days at 20–27 °C (68–80 °F); warmer is quicker. Taste it from day 7 and stop when it is as sour as you like. In the second ferment you pour the finished kombucha into sealed bottles with juice or a little sugar, where the leftover yeast produces carbon dioxide and the fizz. Two to four days at room temperature is typical, then chill.
Pressure builds up quickly in sealed bottles, so use bottles made to hold fizzy drinks, leave some headspace, open them over a sink and refrigerate before opening. For the priming maths of beer-style carbonation see the priming sugar calculator; kombucha is not as predictable, so the amounts here are deliberately small.
Safety first
The Centers for Disease Control and Prevention reported severe illness in people who drank home-brewed kombucha in 1995, and the cases were investigated without a single cause being found. The sensible reading is that contamination and low acidity are the risks. Food regulators treat a pH above 4.6 as the line where harmful bacteria can grow in low-acid foods, and home guides aim lower for kombucha: about 4.2 or below, and below 3.5 once mature. Use the starter liquid, a clean vessel and a cover that lets air in but keeps insects out.
Keep it safe and legal
- Do not use metal containers, lead-glazed ceramic or crystal; the acid dissolves them.
- Discard the batch if you see dry, fuzzy or coloured mould; a stringy brown or smooth cream skin is normal culture.
- Alcohol: kombucha always contains some. In the US a product with 0.5% alcohol by volume or more is regulated as alcohol, which matters if you sell it.
- Who should skip it: pregnant women, young children and people with weak immunity should ask a doctor first.
Kombucha Recipe Calculator FAQ
What is the kombucha ratio of tea to sugar?
A common home ratio is about 8 g of tea and 50–70 g of sugar per litre of water, with 10% of the volume as finished kombucha. This calculator uses 8 g and 60 g as defaults.
How much starter liquid do I need?
About 10% of the batch volume is the usual advice, because the acid in it lowers the pH of the new batch quickly. Using less is slower and raises the risk of contamination.
How much juice for the second ferment?
A range of 10–20 ml of juice per 100 ml of kombucha is common; 15 is the default here. More juice means more sugar for the yeast and more pressure in the bottle.
Can I use honey or other sweeteners?
Plain white sugar is the simplest and most predictable. Honey, artificial sweeteners and flavoured teas can harm the culture or add contaminants, so change one thing at a time.
How do I know it is safe?
Check that the pH is 4.2 or lower, there is no mould, and it smells and tastes pleasantly sour. If in doubt, throw it out. Pregnant women, children and immunocompromised people should avoid homemade kombucha unless a doctor agrees.
Does this tell me the alcohol content?
No. Alcohol depends on time, temperature and sugar. Use the ABV calculator with gravity readings if you need an estimate.