A kombucha batch calculator determines the exact amounts of water, sugar, tea, and starter tea you need for any batch size. Whether you are brewing your first gallon or scaling up to a five-gallon continuous brew, getting the ratios right is the key to consistent, delicious kombucha with great carbonation.
Batch Settings
F1 — Primary Fermentation
Brew sweet tea, add SCOBY and starter, ferment 7-14 days
F2 — Carbonation & Flavoring
Bottle with fruit or juice, seal for 2-4 days
Fermentation Timeline
Temperature Guide
F2 Flavor Combinations
Troubleshooting
Kombucha is too sweet after 7 days
Kombucha tastes too vinegary
No carbonation after F2
Fuzzy mold on the SCOBY surface
SCOBY sinks to the bottom
How to Use the Kombucha Batch Calculator
Brewing great kombucha at home starts with getting the ingredient ratios right. Too much sugar and your brew stays syrupy; too little and the SCOBY runs out of food before fermentation is complete. Our free kombucha batch calculator takes the guesswork out of both first fermentation (F1) and second fermentation (F2), giving you precise measurements for any batch size.
Step 1: Choose your batch size
Select a common size (1, 2, 3, or 5 gallons) or enter a custom volume in liters. One gallon is the most popular starting size for beginners because it fits in a standard glass jar and produces enough kombucha for about a week of drinking. The calculator instantly adjusts all ingredient amounts to match your chosen volume.
Step 2: Select your tea type
Black tea is the classic choice and produces the most robust flavor. Green tea yields a lighter, more delicate brew. Oolong sits between the two, while white tea produces the mildest kombucha. The calculator adjusts the recommended tea quantity slightly by type, since green and white teas are typically used in smaller amounts to avoid bitterness.
Step 3: Set your starter tea percentage
Starter tea is acidic liquid from a previous batch that protects your new brew from harmful bacteria. The standard recommendation is 10% of your total batch volume, but new brewers or those in warm climates may want to increase this to 15-20% for extra protection. The slider lets you adjust between 10% and 20%.
Step 4: Review your F1 ingredients
The calculator shows the exact amounts of water, sugar, tea bags (or loose leaf tea), starter tea, and SCOBY needed for your primary fermentation. Water is automatically reduced to account for the starter tea volume, so your total batch lands at the target size.
Step 5: Plan your F2 bottling
After F1 is complete, the calculator tells you how many bottles you will need and how much fruit juice or puree to add for flavoring and carbonation. Choose between 16 oz and 12 oz bottles. The fruit juice percentage (10-20% of bottle volume) provides both flavor and residual sugar for natural carbonation in sealed bottles over 2-4 days.
All calculations run locally in your browser. Nothing is stored or sent anywhere, so your brewing details remain completely private. Bookmark this page to return for every new batch.
FAQ
Is this kombucha calculator really free?
Yes, the kombucha batch calculator is completely free with no limits and no account required. Use it for every brew. All calculations happen in your browser and nothing is stored or sent anywhere.
Is my data safe and private?
Absolutely. Every calculation runs entirely in your browser using JavaScript. No data is sent to any server, stored in any database, or shared with anyone. You can even use the tool offline once the page has loaded.
How much sugar should I use per gallon of kombucha?
The standard ratio is 1 cup (200g) of white cane sugar per gallon of kombucha. This gives the SCOBY enough food to ferment properly while producing a balanced flavor. Using less sugar results in a weaker, thinner brew, while more sugar can over-ferment and taste too vinegary.
How much starter tea do I need for kombucha?
You need 10-15% of your total batch volume as starter tea from a previous batch. For a 1-gallon batch, that is about 1.5 to 2.5 cups. Starter tea provides the acidic environment that protects your brew from harmful bacteria during the early stages of fermentation.
What is the difference between F1 and F2 fermentation?
F1 (first fermentation) is the primary brew where sweet tea, a SCOBY, and starter tea ferment for 7-14 days in a jar covered with cloth. F2 (second fermentation) is when you bottle the finished kombucha with fruit or juice in sealed bottles for 2-4 days to build carbonation and add flavor.
What temperature is best for brewing kombucha?
The ideal temperature range is 75-85 degrees Fahrenheit (24-29 degrees Celsius). Below 70 F, fermentation slows dramatically and increases mold risk. Above 90 F, the brew ferments too fast and becomes vinegary. A consistent temperature in the mid-to-upper 70s produces the best results.
How do I know when my kombucha is done fermenting?
Taste it starting around day 7. It should be slightly tart with a mild sweetness — not overly sweet and not sharply vinegary. The pH should be between 2.5 and 3.5. If it tastes too sweet, let it ferment longer. If it tastes too vinegary, shorten your next brew cycle by a day or two.
Can I use honey or other sweeteners instead of sugar?
White cane sugar works best because the SCOBY culture is adapted to break down sucrose efficiently. Raw honey contains antibacterial properties that can harm the SCOBY. You can experiment with brown sugar or coconut sugar once you have a healthy backup SCOBY, but avoid artificial sweeteners entirely as they provide no food for fermentation.