Terrarium Substrate Layer Calculator
Calculate the volume and depth of each substrate layer for your terrarium based on container dimensions and terrarium type.
A properly layered terrarium substrate is essential for plant health, drainage, and preventing root rot. Each layer serves a specific purpose, and the proportions depend on your container size and terrarium type (open vs. closed).
Standard Terrarium Layer Structure (bottom to top)
| Layer | Material | Purpose | Typical Depth % |
|---|---|---|---|
| 1. Drainage | Pebbles, LECA, gravel | Prevents waterlogging | 15–20% of total height |
| 2. Separation | Mesh screen or charcoal | Stops soil from sinking into drainage | 2–5% (thin layer) |
| 3. Activated Charcoal | Horticultural charcoal | Filters water, prevents odors | 3–5% |
| 4. Growing Medium | ABG mix, potting soil | Where roots grow | 25–35% |
| 5. Top Dressing | Sphagnum moss, leaf litter | Retains moisture, aesthetics | 5–10% |
Volume Formula
For a rectangular container: Volume (liters) = Length (cm) x Width (cm) x Depth (cm) / 1000
For a cylindrical container: Volume (liters) = pi x Radius^2 (cm) x Depth (cm) / 1000
Each layer’s volume = Total volume x (layer percentage / 100).
Worked Example: 30cm x 20cm x 25cm Closed Tropical Terrarium
Total interior volume = 30 x 20 x 25 = 15,000 cm^3 = 15 liters. Usable height for substrate: roughly 60% of total height = 15 cm.
- Drainage layer (20%): 15 x 0.20 = 3.0 cm deep = 1.8 liters of LECA
- Separation mesh: thin sheet, negligible volume
- Charcoal layer (5%): 15 x 0.05 = 0.75 cm = 0.45 liters of charcoal
- Growing medium (30%): 15 x 0.30 = 4.5 cm = 2.7 liters of ABG mix
- Top dressing (5%): 15 x 0.05 = 0.75 cm = 0.45 liters of sphagnum moss
- Remaining 40% = open air space for plant growth above substrate
Terrarium Type Adjustments
Closed tropical terrariums need thicker drainage layers (20%) because excess moisture cannot evaporate. Open arid terrariums need thinner drainage (10–15%) but deeper growing medium with added perlite or sand for faster drainage. Bioactive vivariums require a deeper substrate overall (at least 7–8 cm of growing medium) to support microfauna like springtails and isopods.
Material Quantities by Weight
| Material | Approximate Density | 1 Liter Weighs |
|---|---|---|
| LECA (expanded clay) | 0.3–0.5 kg/L | ~400g |
| Activated charcoal | 0.2–0.4 kg/L | ~300g |
| ABG mix | 0.4–0.6 kg/L | ~500g |
| Sphagnum moss (dry) | 0.03–0.05 kg/L | ~40g |
| Pea gravel | 1.5–1.7 kg/L | ~1,600g |
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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