fishkeepingguide
The substrate planner

Build a better
substrate plan.

Measure the footprint. Shape the bed. Pin one result and see what your next change adds.

See the formula ↓
01

Your tank’s footprint

Measure inside the glass. Example dimensions are editable.

cm
Inside glass to inside glass.
cm
The front-to-back measurement.
Try a footprint
02

Your substrate bed

How do I choose an actual depth?

Start with the material’s job and its current instructions. A complete bed and a concentrated layer under gravel are different plans.

  • Tropica Aquarium Soil ↗ is a complete substrate. The maker uses an 8 cm depth in a volume example; that is an example, not a depth rule for every aquarium.
  • Tropica Plant Growth Substrate ↗ is specified as a 1 cm nutrient layer beneath gravel. That 1 cm is one layer, not the complete gravel-covered bed.

Check the exact product, planting plan and needs of the intended inhabitants before settling on a depth. For a layered system, calculate each material separately.

Manufacturer instructions checked November 9, 2026. The movable geometry examples demonstrate quantities, not recommended care settings.
cm
Your chosen depth for this setup.
%
Optional. Added once, before whole-bag rounding.
03Weight, bags & cost Optional

Volume works without these details. Use the actual bag label or a documented bulk density.

No universal density is assumed for sand, gravel or aquasoil.
Leave blank if unknown.
Match the quantity printed on the bag.
USD
Your price, not a store quote.
USD
Blank means unknown, not free.
YOUR PLAN9.00 L
The method stays visible

Know what
the numbers mean.

The plan starts with volume. Weight and buying quantities follow from the assumptions you enter.

Liters, kilograms & bags
The volume formula

Inside length (cm) × inside width (cm) × average depth (cm) ÷ 1,000 = liters.

For an even slope, average depth = (front + back) ÷ 2. Each inch converts to exactly 2.54 cm.

Weight, bags and price

Weight in kg = liters × bulk density in kg/L. A density range produces a weight range. Divide by the matching bag quantity and round upward to whole bags, using unrounded results.

Bag subtotal = bags × your entered price. Shipping stays unknown until entered. There are no live merchant prices.

What is not assumed

No product density, care depth, hidden spare allowance or free shipping is assumed. A preset is an editable footprint, not the dimensions of every tank with a gallon label.

Bulk density includes spaces between grains. Pure mineral density is not interchangeable with it.

Check the arithmetic

30 × 20 × 5 cm = 3.00 L
20 × 10 × 2 inches = 6.5548256 L
30 × 20 cm with an even 2-to-8 cm slope = 3.00 L

Mathematical examples, not product measurements.

Sources: NIST volume units ↗ and Tropica’s volume method ↗.

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