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Terrarium Building Calculator — Layers, Materials & Cost

Plan every layer of your terrarium build with precise material quantities and a complete shopping list

Total Estimated Cost

$44.00

Materials

$32.00

Plants

$12.00

Units

Cost Breakdown

$44.00
total estimated cost
Materials
$32.00
substrate + layers
Plants
$12.00
3 small (2" plugs)

Layer Depths (bottom to top)

LayerDepthVolume
Drainage (pebbles)0.89"3.1 cups
Activated charcoal0.22"0.8 cups
Sphagnum moss barrier0.22"0.8 cups
Soil mix2.13"1.9 qt
Decorative top layer0.53"1.9 cups
Total Fill4.0"3.5 qt

Layer Diagram

Decorative top layer0.53"
Soil mix2.13"
Sphagnum moss barrier0.22"
Activated charcoal0.22"
Drainage (pebbles)0.89"

Plant Capacity

Usable planting area50.3 sq in
Spacing (small (2" plugs))2" apart
Max plants that fit12
Plants used in estimate3

Shopping List

ItemQtyCost
River pebbles (5 lb bag)1$5.00
Horticultural charcoal (2 qt)1$8.00
Sphagnum moss (150 g bag)1$6.00
Tropical soil mix (8 qt)1$8.00
Decorative moss/stones1$5.00
Small (2" plugs) plants3$12.00
Total$44.00

DIY vs Pre-Made Cost

DIY Build$44
Pre-Made (small)$35
Pre-Made (large)$75

DIY terrariums cost $0–$31 less than pre-made options of similar size

Maintenance Schedule

Watering: Mist lightly once per month. Condensation on glass means adequate humidity.
Light: Bright indirect light only. Direct sunlight overheats sealed containers and cooks plants.
Pruning: Trim plants when they touch the glass. Remove dead leaves promptly to prevent mold growth.
Charcoal layer: Activated charcoal filters bacteria and odors. It lasts 1–2 years before needing replacement.

Building Tips

Drainage is crucial: Without a drainage layer, standing water causes root rot. Use pebbles or LECA clay balls at the bottom.
Moss barrier: Sphagnum moss between charcoal and soil prevents soil from sifting into the drainage layer over time.
Fill height: Never fill more than half the container. Plants need vertical space to grow and air circulation above the soil.
Plant selection: Tropical plants only: fittonia, ferns, selaginella, moss, and peperomia thrive in humidity.

What You'll Need

Amiloe Digital Postal Scale 66lb/0.1oz

Amiloe Digital Postal Scale 66lb/0.1oz

$15-$224.6
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888 Display Kraft Jewelry Boxes 50pk

888 Display Kraft Jewelry Boxes 50pk

$12-$184.5
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Amiloe Digital Postal Scale 66lb/0.1oz

Amiloe Digital Postal Scale 66lb/0.1oz

$15-$224.6
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888 Display Kraft Jewelry Boxes 50pk

888 Display Kraft Jewelry Boxes 50pk

$12-$184.5
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Example Calculations

18" Cylinder Jar — Closed Tropical (3 small plants)

Inputs

Container ShapeCylinder / Jar
Diameter8 inches
Height10 inches
Terrarium TypeClosed (Tropical)
Plant Count3
Plant SizeSmall (2" plugs)

Result

Total Cost$44.00
Material Cost$32.00
Plant Cost$12.00 (3 plants)
Fill Height4.0"
Total Volume3.5 qt

A closed 8" cylindrical terrarium filled to 40% height needs about 3.5 quarts of substrate across five layers. One bag each of pebbles, charcoal, moss, soil, and decorative topping plus three small plants totals $44.

212" x 8" Rectangular — Open Succulent (4 medium plants)

Inputs

Container ShapeRectangular
Dimensions12" L × 8" W × 10" H
Terrarium TypeOpen (Succulent/Arid)
Plant Count4
Plant SizeMedium (4" pots)

Result

Total Cost$56.00
Material Cost$32.00
Plant Cost$24.00 (4 plants)
Fill Height4.0"
Total Volume6.7 qt

A rectangular open terrarium (96 sq in base) holds about 6.7 quarts of substrate. Four medium succulents at 3-inch spacing fit comfortably in the 96 sq in planting area, bringing the total to $56.

310" Bowl — Closed Tropical (2 large plants)

Inputs

Container ShapeBowl / Sphere
Diameter10 inches
Terrarium TypeClosed (Tropical)
Plant Count2
Plant SizeLarge (6" pots)

Result

Total Cost$52.00
Material Cost$32.00
Plant Cost$20.00 (2 plants)
Fill Height4.0"
Max Plants3 large plants fit

A 10-inch bowl has about 78 sq in of planting area. At 4.5-inch spacing, up to 3 large plants fit, though 2 gives each plant more room to spread. Materials total $32 plus $20 for two large plants.

Frequently Asked Questions

Q

What layers does a terrarium need?

A terrarium has five layers from bottom to top: drainage pebbles (about 15% of fill height, minimum 1 inch), activated charcoal (5%, minimum 0.25 inch), sphagnum moss barrier (5%, minimum 0.25 inch), soil mix (60%), and a decorative top layer (15%, about 0.5 inch). Each layer serves a specific purpose in water management and plant health.

  • Drainage layer: 1–2" of pebbles or LECA — prevents standing water and root rot
  • Charcoal layer: 0.25–0.5" of activated charcoal — filters bacteria, toxins, and odors
  • Moss barrier: 0.25–0.5" of sphagnum moss — prevents soil from sifting into drainage
  • Soil layer: 2–4" of appropriate mix — tropical mix for closed, cactus mix for open
  • Decorative layer: 0.5–1" of moss, stones, or sand — aesthetics and moisture retention
LayerClosed TerrariumOpen Terrarium
DrainagePebbles or LECACoarse gravel or perlite
CharcoalRequired (humidity traps odors)Recommended
Moss BarrierSphagnum mossOptional (less water movement)
SoilTropical/peat-based mixCactus/succulent mix
Top LayerSheet moss, fern bitsDecorative stones, sand
Q

How much does it cost to build a terrarium?

A DIY terrarium costs $25–$55 depending on container size and plant count. Materials (pebbles, charcoal, moss, soil, decorative topping) run $20–$35 total, and small plants add $3–$10 each. Pre-made terrariums sell for $35–$75+, so building your own saves 30–60%.

  • River pebbles: ~$5 per 5 lb bag — one bag covers most small-to-medium containers
  • Activated charcoal: ~$8 per 2 qt bag — one bag lasts several builds
  • Sphagnum moss: ~$6 per 150 g bag — thin layer uses very little
  • Soil mix: ~$8 per 8 qt bag — largest volume layer, one bag for most builds
  • Small plants (2" plugs): $3–$5 each — fittonia, moss, and small ferns are cheapest
Build TypeDIY CostPre-Made PriceSavings
Small (6" jar)$25–$35$35–$5025–50%
Medium (8–10" jar)$35–$45$50–$7530–45%
Large (12"+ vessel)$45–$65$75–$12040–60%
Q

How full should I fill my terrarium?

Fill a terrarium to 33–40% of the container height for closed types and 30–35% for open types. Never fill more than half. Plants need vertical space above the soil for growth, and closed terrariums need air volume for the water cycle to function. An 8-inch tall jar should have about 3–4 inches of total substrate.

  • Closed tropical: fill to about 40% of container height for humidity cycling
  • Open succulent: fill to about 35% — less moisture means less substrate needed
  • Never exceed 50% fill — plants need room to grow upward
  • Account for all 5 layers when measuring fill height, not just soil
  • An 8" tall jar = ~3.2" fill (closed) or ~2.8" fill (open) including all layers
Q

How many plants fit in my terrarium?

Plant count depends on container diameter and plant size. Small 2-inch plugs need 2 inches of spacing, medium 4-inch pots need 3 inches, and large 6-inch pots need 4–5 inches between plants. An 8-inch diameter jar fits about 12 small plants, 5 medium plants, or 2 large plants based on area calculations.

  • Small plants (2" plugs): 2" spacing — ~12 fit in an 8" diameter container
  • Medium plants (4" pots): 3" spacing — ~5 fit in an 8" diameter container
  • Large plants (6" pots): 4.5" spacing — ~2 fit in an 8" diameter container
  • Formula: max plants = floor(usable area / spacing²)
  • Leave at least 0.5" gap from the container wall for air circulation
Container DiameterSmall PlantsMedium PlantsLarge Plants
6"731
8"1252
10"1983
12"28125
Q

What is the difference between closed and open terrariums?

Closed terrariums have a sealed lid that creates a self-sustaining water cycle — moisture evaporates, condenses on the glass, and drips back to the soil. They suit tropical plants like ferns, fittonia, and moss. Open terrariums have no lid, providing airflow for succulents, cacti, and air plants that need dry conditions.

  • Closed: self-cycling humidity, mist once per month, tropical plants only
  • Open: dry environment, water weekly, succulents and cacti only
  • Closed terrariums must never sit in direct sunlight — sealed glass overheats
  • Open terrariums tolerate more light and are more forgiving for beginners
  • Charcoal layer is critical in closed builds to prevent bacterial buildup
Q

Why is activated charcoal needed in a terrarium?

Activated charcoal acts as a natural filter in the drainage layer, absorbing bacteria, toxins, and odors from standing water. Without it, closed terrariums develop foul smells within weeks as organic matter decomposes in the trapped moisture. A 0.25–0.5 inch layer between the drainage pebbles and sphagnum moss lasts 1–2 years.

  • Absorbs bacteria and organic toxins from water cycling through the substrate
  • Prevents foul odors from anaerobic decomposition in the drainage layer
  • Lasts 1–2 years before needing replacement — if smell returns, it is time
  • Horticultural charcoal is $8 per 2 qt bag — enough for 3–5 terrariums
  • Essential for closed terrariums; recommended but optional for open builds

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Last Updated: Mar 16, 2026

This calculator is provided for informational and educational purposes only. Results are estimates and should not be considered professional financial, medical, legal, or other advice. Always consult a qualified professional before making important decisions. UseCalcPro is not responsible for any actions taken based on calculator results.

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