Aquarium Substrate Calculator
Created by: Sophia Bennett
Last updated:
Calculate exactly how much gravel, sand, or planted substrate you need for your aquarium. Get weight in pounds and kilograms, plus bag quantities based on your tank dimensions and desired substrate depth for fish-only or planted setups.
Aquarium Substrate Calculator
AquariumCalculate how much gravel, sand, or soil your tank needs
Tank Dimensions
Substrate Type
Related Calculators
What is an Aquarium Substrate Calculator?
An Aquarium Substrate Calculator determines exactly how much gravel, sand, or planted tank substrate you need based on your tank dimensions and desired depth. Buying the right amount prevents costly overbuying or frustrating return trips for more.
This calculator accounts for different substrate densities - sand is heavier per volume than gravel, and specialty planted substrates vary widely. Get results in pounds and kilograms, plus bag quantities based on common package sizes.
Whether you're setting up a new aquarium or refreshing substrate in an existing tank, accurate calculations ensure proper depth for aesthetics, plant health, and beneficial bacteria colonization.
Substrate Calculation Formulas
Volume Formula:
Substrate Volume (cubic inches) = Length × Width × Depth
Weight Calculation:
Weight (lbs) = Volume (cubic feet) × Density (lbs/cubic foot)
Common Densities:
• Gravel: 90 lbs/cubic foot
• Sand: 100 lbs/cubic foot
• Planted substrate: 50-70 lbs/cubic foot
• Crushed coral: 85 lbs/cubic foot
Conversion:
1 cubic foot = 1,728 cubic inches = 7.48 gallons
Substrate Calculation Examples
Example 1: 29-Gallon Standard Tank with Gravel
Dimensions: 30" × 12" × 2" depth
Volume: 720 cubic inches = 0.42 cubic feet
Weight: 0.42 × 90 = 37.5 lbs of gravel
Buy: Two 20-lb bags
Example 2: 55-Gallon Planted Tank
Dimensions: 48" × 13" × 3" depth
Volume: 1,872 cubic inches = 1.08 cubic feet
Planted substrate: 1.08 × 60 = 65 lbs
Buy: Three 20-lb bags or equivalent
Example 3: 75-Gallon Cichlid Tank with Sand
Dimensions: 48" × 18" × 2.5" depth
Volume: 2,160 cubic inches = 1.25 cubic feet
Weight: 1.25 × 100 = 125 lbs of sand
Buy: Three 50-lb bags
Substrate Selection Applications
Fish-Only Community Tanks
Standard gravel at 2-inch depth works well. Choose colors that complement your fish. Larger gravel (pea-sized) is easier to vacuum than fine gravel.
Planted Aquariums
Use nutrient-rich substrates at 3-4 inch depth. Consider layering: nutrient soil on bottom, capped with gravel or sand. Calculate total for both layers.
Cichlid and Rift Lake Tanks
Aragonite sand or crushed coral buffers pH for African cichlids. Calculate 2-3 inch depth, accounting for fish that dig and rearrange substrate.
Shrimp and Nano Tanks
Fine substrates allow shrimp to forage naturally. Active substrates can lower pH for Caridina species. Use 1.5-2 inch depth in nano tanks.
Tips for Aquarium Substrate
Buy Extra: Purchase 10-15% more than calculated for slopes, settling, and future maintenance replacements.
Rinse Thoroughly: Wash substrate in batches until water runs clear. This prevents cloudy water that takes days to settle.
Add Water Carefully: When filling a new tank, pour water onto a plate or bag to avoid disturbing carefully placed substrate.
Consider Maintenance: Gravel is easier to vacuum than sand. Sand can compact and develop anaerobic pockets - stir occasionally.
Frequently Asked Questions
How deep should aquarium substrate be?
For most tanks, 2-3 inches is ideal. Fish-only tanks can use 1-2 inches. Planted tanks need 2-4 inches for root development. Deep substrate beds (4+ inches) risk anaerobic pockets unless using specialized substrates designed for depth.
How many pounds of gravel do I need per gallon?
The general rule is 1-2 pounds per gallon for 2-3 inch depth. A 29-gallon tank needs roughly 30-60 lbs of gravel. Our calculator provides exact amounts based on your specific tank dimensions and desired depth.
What's the difference between gravel and sand substrate weight?
Sand is denser than gravel - sand weighs about 100 lbs per cubic foot while gravel weighs 85-95 lbs. For the same depth, you'll need more pounds of sand than gravel. Our calculator adjusts for substrate type.
Can I mix different substrates in my aquarium?
Yes, but heavier substrates sink over time. Put heavier materials (like plant substrate) on bottom, capped with gravel or sand. Use barriers or slopes intentionally. Mixing equal-weight substrates works best for uniform appearance.
How much substrate do I need for a planted tank?
Planted tanks need 2-4 inches of nutrient-rich substrate for healthy root growth. Heavy root feeders like swords and crypts need 3-4 inches. Use specialized planted tank substrates or cap nutrient soil with gravel.
Should I slope the substrate in my aquarium?
Sloping from back (higher) to front (lower) creates depth perception and visual interest. Plan for 3-4 inches at back, 1-2 inches at front. This also helps debris collect at the front for easier cleaning.
How do I calculate substrate for a non-rectangular tank?
For bow front tanks, calculate rectangular portion plus bow area. For hexagonal tanks, use the hexagon area formula. Our calculator supports multiple tank shapes or lets you enter surface area directly.
Do I need to wash aquarium substrate before use?
Yes, always rinse gravel and sand until water runs clear - dusty substrate clouds water for days. Some planted substrates shouldn't be rinsed as they contain nutrients. Check manufacturer instructions for specialty substrates.
Sources and References
- Aquarium Science, "Substrate Selection and Depth Guidelines", 2024
- Aquatic Gardeners Association, "Planted Tank Substrate Requirements", AGA, 2024
- Tropical Fish Hobbyist, "Substrate Guide for Home Aquariums", TFH, 2024