The Golden Kombucha Ratio
Almost every reliable kombucha recipe is a scaled version of one rule: for every 1 gallon (128 oz) of finished tea, use about 1 cup of plain white sugar (around 200 grams), 8 tea bags (or roughly 2 tablespoons of loose-leaf tea), and 1 to 2 cups of mature starter liquid plus your SCOBY. This calculator takes that gallon-based formula and shrinks or grows it to fit your exact jar, whether you brew in a 32 oz mason jar or a 2 gallon crock.
sugar (g) = 200 x (jar oz / 128) x strength
Strength simply nudges the tea and sugar up or down: Light uses 85% of the classic load for a mellow, faster-finishing brew, while Strong uses 120% for a punchier, more acidic result. The starter liquid is held at a fixed 1 cup per half gallon (about 12.5% of volume) because it controls the starting pH, not the flavor, and that acidity is what protects your batch from mold during the first few days.
Why The Sugar Is Not For You
New brewers often panic at "1 cup of sugar," but the sugar is food for the yeast and bacteria, not for the drinker. Over a 7 to 14 day ferment the SCOBY consumes most of it, leaving a finished kombucha with only a few grams of residual sugar per 8 oz serving. Warmer kitchens (75 to 85 F) ferment faster and eat more sugar; cooler rooms run slower.
Reading Your Numbers
The "Sweet Tea (water)" figure is how much water to brew and sweeten before topping off, calculated as your jar volume minus the starter liquid. Brew a strong concentrate, dissolve the sugar while hot, steep the tea, then cool to room temperature before adding the starter and SCOBY. Pouring hot tea over a SCOBY will kill it, so always wait until the sweet tea is below 90 F.
Frequently Asked Questions
How much sugar do I really need per gallon?
The standard is 1 cup, which is about 200 grams of plain white sugar, per gallon of finished kombucha. This calculator scales that exactly to your jar size, so a half-gallon batch needs roughly 100 grams and a quart needs about 50 grams.
Can I use less sugar to make it healthier?
You can drop to the Light setting, but do not cut sugar drastically below it. The sugar feeds the SCOBY rather than sweetening the final drink, and starving the culture leads to a weak, mold-prone batch. Most of the sugar is gone by the time the kombucha is ready to drink.
How much starter liquid should I add?
Use about 1 cup of mature, unflavored kombucha per half gallon, which this tool sets automatically. The starter lowers the pH below 4.5 right away, creating an acidic environment that fends off mold and bad bacteria during the vulnerable first days of fermentation.
What kind of tea works best?
Plain black tea is the most reliable and gives the strongest SCOBY, though green tea or a black-green blend also work well. Avoid teas with added oils, like Earl Grey or most herbal blends, because the oils can damage your culture over repeated batches.
Practical Guide for Kombucha Brewing Calculator
Temperature is the single biggest lever you control after the ratio. Kombucha ferments happily between 75 and 85 F; below 70 F it crawls and risks mold, while above 90 F it can turn harshly sour and stress the yeast. A simple seedling heat mat or a warm cupboard keeps a steady temperature and makes your ferment-length estimate far more accurate.
Taste, do not guess, as you approach the end of the window. Starting around day 7, draw a little out with a straw each day. When it hits the balance of sweet and tart you like, it is done; warmer batches reach that point faster than the 10-day default. Once you bottle for a second ferment with fruit or juice, expect another 2 to 4 days at room temperature to build fizz.
Reserve your next starter before you flavor anything. Set aside roughly 1 to 2 cups of the plain, finished kombucha along with the SCOBY for your following batch. Keeping that liquid unflavored and acidic is the easiest insurance against a failed brew, and it lets you reuse the exact ratios from this calculator indefinitely.
Quick Checklist
- Use plain white sugar and plain black or green tea, no oils or flavorings in the first ferment.
- Cool the sweet tea below 90 F before adding the SCOBY and starter liquid.
- Cover the jar with a tight-weave cloth and band, never an airtight lid, during the first ferment.
- Always reserve 1 to 2 cups of unflavored kombucha plus the SCOBY as starter for the next batch.