Jar & Vessel Volume Calculator
Pick the shape closest to your container, enter its dimensions, and get its total volume plus a realistic usable-substrate estimate.
Vessel volume
Reading the result
The total volume is the vessel’s full geometric capacity — useful for comparing containers or checking a listing’s stated size. The usable substrate volume applies the fill factor to that number, giving a more realistic sense of how much drainage material, soil, and moss you’ll actually be placing inside.
For an irregular container that doesn’t match any of the four shapes cleanly, pick whichever shape is the closest approximation — the volume of most terrarium vessels is dominated by their main body, so a reasonable approximation is usually close enough for planning purposes.
Frequently Asked Questions
Why does the vessel shape matter?
A cylinder, a sphere, and a rectangular tank hold volume very differently even at the same height and width, because the formulas for their volume are different. Picking the shape closest to your actual container gives a far more accurate number than assuming it's a simple box.
What is a bell jar / cloche shape here?
It's modelled as a cylinder with a rounded dome on top — a straight-sided glass body topped by a hemisphere, which is how most classic bell jars and cloches are shaped. Measure the cylindrical part's height separately from the dome; the dome's volume is calculated from the same diameter automatically.
What is the 'fill factor' for?
You never pack a terrarium to the very rim — you need headspace for air circulation, watering room, and plant growth. The default 60% fill factor estimates how much of the vessel you'd actually use for the substrate stack and plants, leaving the rest as open space above.
Why does it show gallons as well as litres?
Vessel sizes and drainage material are sold in both metric and US units depending on the retailer, so having both numbers on hand makes it easier to check a product's stated capacity against your container.
Educational planning tool only — a geometric estimate from the dimensions you enter, not a substitute for measuring your specific container's stated capacity.