get FermentCalc

Jar Capacity Calculator

Enter a fermentation jar's inner diameter and the height you plan to fill to get its volume, how much chopped vegetables actually occupy, and the brine plus salt that keeps everything submerged.

cm
cm

Measure to the level you will actually fill, not the rim: ferments need headspace for bubbling brine and a weight above the vegetables, so most jars stop 3-5 cm below the lid.

%

Chopped, packable shapes run high - shredded cabbage reaches 70-80% - while whole cucumbers or cherry tomatoes settle near 55-65%. The 65% default is a safe middle ground for mixed cuts.

%

Typical lacto-fermentation brines run 2-5% salt by weight. The calculator assumes brine weighs about 1 g per ml, so the salt figure is a scale number, not a spoon number.

Results

Total jar capacity
0.76L
Usable vegetable volume
0.5 L
Brine to fill the voids
0.27 L
Salt for that brine
5.3 g

How the jar math works

A jar is a cylinder, so volume = pi x (diameter / 2) squared x height. Vegetables never pack solid: the packing efficiency splits that volume into vegetable space and void space between the pieces. The calculator sizes the brine batch at the vegetable space so the voids stay filled and everything stays submerged, then weighs the salt as brine volume x salinity.

volume (L) = pi x r^2 x h / 1000; usable = volume x packing; salt (g) = brine (L) x salinity % x 10

Once the jar is full, the brine calculator refines the salt for water-weight or total-weight bases, and the vegetable salt ratio calculator handles dry-salted ferments like sauerkraut and kimchi that never see added water.

Frequently asked questions

Why do I need brine equal to the vegetable space?

The brine's job is to keep every piece submerged, so it fills the voids between the vegetables and stands a little above them. Sizing the batch at the vegetable volume gives you enough with a safety margin - any leftover keeps in the fridge for topping up as evaporation lowers the level.

What packing efficiency should I use?

It depends on the shape: tightly shredded cabbage tamps down to 70-80%, uniform sticks like carrots or cucumber spears sit around 60-65%, and whole round vegetables waste the most space near 55%. Start with 65%, then weigh your first real pack to calibrate your own jars.

How much headspace should I leave in a fermentation jar?

Plan on the fill height stopping 3-5 cm below the lid: active ferments bubble and rise during the first days, and a weight plus a layer of brine must sit above the vegetables the whole time. Wide-mouth jars with glass weights make that headspace far easier to manage than fill-to-the-rim packing.