Terrarium Layer Calculator Tool

Terrarium Layer Calculator: Know Every Layer Before You Build

Anyone who’s tried building a terrarium knows the struggle. To build one that survives starts weeks before buying plants. Planning starts with knowing how much gravel, charcoal, mesh, and substrate you’ll need to fill your container. Rather than rely on guesswork, dive into the specifics with Terrarium Layer Calculator and have volumes for each layer presented to you in seconds.

How Terrarium Layer Calculator Works

Terrarium Layer Calculator takes the dimensions of your container and spits out how much of each material you need. Input the shape (cube, cylinder, sphere, rectangular tank), size, and desired depth of each layer and get back the volume of drainage rocks, activated charcoal, barrier mesh, and soil mix you should add from the top down. Forget buying too much LECA or running out of substrate in the middle of building a terrarium; get the exact amount based on your actual container.

Why You Should Care About Layer Math

Layers within closed or open terrariums serve individual purposes. Getting the proper depth for each layer is important for your plant’s survival. Too little drainage layer and water pools in the soil, leading to root rot. Too much and you’re taking away from how much soil your plant has to grow.

Most terrariumers know a good rule of thumb is to have the drainage layer be approximately one fourth of the depth of the soil layer. However, this still requires you to calculate volumes for every round jar or oval globe you build. C’est où la calculatrice?

Calculator Layers

Drainage

Gravel, pea pebbles, LECA, etc. that serve to keep excess water away from your plant’s roots.

Filter / Charcoal

Thin layer of activated charcoal. Helps absorb impurities, odors, and the occasional rogue mold spore.

Mesh Barrier

Hardware cloth, burlap, landscape cloth, etc. that keeps your soil from mixing into your drainage area.

Substrate

Potting soil, perlite, coco peat, ABG mix… anything that’s deep enough to anchor your plants in place.

Using the Terrarium Layer Calculator

1. Grab a ruler and measure the length, width, and height of the inside of your container. Inputs are completely custom, so use whatever units you like.
2. Decide how deep you want each layer to be. Terrarium beginners can trust that the defaults suggested in the calculator are taken from popular terrarium instructions.
3. Pull up the resulting volumes for each material before heading to the store. Buy exactly what you need and wonder why everyone is so interested in your terrarium.

Who Needs It?

Those building their first closed jar terrarium can skip memorizing ratios and use this as a baseline to start from.

Those who have been keeping for years and build bioactive vivariums or paludariums can use this to help scale up to larger setups where guessing at amounts can get expensive fast.

Nurseries and educators who host terrarium workshops can even pre-measure materials for customers and students.

Example

In a cylinder 4 liter jar with a 1″ drainage layer, thin layer of charcoal, and 2.5″ of substrate, you’ll need the following, represented in gallons or liters:

Visualize that coming together using these helpful visuals from Josh’s Frogs Substrate Calculator. The same math our NEHERP team uses for determining substrate volumes in vivariums — only we’ve tailored it to work with any shaped decorative terrarium.