Free terrarium soil calculator. Enter length, width and soil depth to find the soil volume and 5 litre bags you need.
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Enter the length, width and soil depth of your terrarium in centimetres. Volume in litres is length times width times depth divided by 1000, and bags are rounded up to whole 5 litre bags. Buy a little extra if you want a deeper layer at the back of the terrarium.
Terrarium soil volume is a simple box volume: length times width times depth, divided by 1000 to give litres. A 30 by 20 cm base with 5 cm of soil needs 3000 cubic centimetres, which is 3 litres, and one 5 litre bag covers it. The same formula works for aquarium soil and raised beds, which is why competitor guides repeat it across plant and tank pages.
Most guides recommend 2 to 3 inches, about 5 to 7.5 cm, of soil for terrarium plants, with deeper soil for deep rooted plants. The soil layer should at least match the depth of the largest root ball you plant. Tropical setups often use 4 to 6 inches of substrate for stronger root growth, while small closed terrariums do well at the lower end. The right soil amount for a closed terrarium is exactly the volume this calculator gives, with no extra layer needed.
A terrarium has no drainage holes, so it needs layers instead. Start with a drainage layer of gravel, small stones or LECA clay balls, then a thin layer of activated charcoal, then a moss or mesh barrier, then soil. A common terrarium soil mix recipe blends potting soil with perlite and a little sand for drainage. The barrier stops soil from sinking into the drainage layer, and the charcoal helps keep the closed environment fresh.
The drainage layer should be about 2 to 3 inches deep in larger enclosures, and about 1 to 2 inches in small jars, using gravel, scoria, or LECA. In a bioactive terrarium the drainage layer is crucial, since it keeps the soil from waterlogging and protects the clean-up crew. LECA is popular because it is light, porous, and reusable, and it holds excess water away from roots so plants do not get wet feet. Always put a mesh screen between drainage and soil to stop the layers mixing.
Soil bags are sold by volume, so divide your litres by the bag size and round up: a 12 litre need at 5 litres per bag takes 3 bags. Buy 10 to 15 percent extra substrate to cover settling after the first watering, since fresh soil compacts and you will want to top it up. Small terrariums need 1 litre, medium ones about 4 litres, and large ones 10 litres or more.
Take a 40 by 30 cm terrarium with 10 cm of soil. Volume is 40 times 30 times 10 divided by 1000, which is 12 litres, and bags are ceil of 12 divided by 5, which is 3 bags of 5 litres. The same terrarium at 5 cm depth would need only 6 litres, or 2 bags.
Length times width times depth divided by 1000 gives litres. A 30 by 20 cm terrarium with 5 cm of soil needs 3 litres.
About 2 to 3 inches, or 5 to 7.5 cm, for most plants, deeper for tropical setups and deep rooted plants.
Yes. Without drainage holes, a layer of gravel or LECA keeps water away from roots and prevents root rot.
About 2 to 3 inches in larger enclosures and 1 to 2 inches in small jars, using gravel, stones, or LECA.
A thin layer of activated charcoal, then a moss or mesh barrier, which stops soil sinking into the drainage layer.
Divide the litres by the bag size and round up. A 12 litre terrarium needs 3 bags of 5 litres.
Yes, about 10 to 15 percent extra, since fresh soil settles after watering and needs topping up.
A purpose made terrarium mix drains better and stays healthier than plain garden soil, which can compact and stay soggy.